nouveau-ddx: Improvements to DRI2 kms pageflip and swapbuffers support.

nouveau-ddx: Improvements to DRI2 kms pageflip and swapbuffers support.

[Mario Kleiner]

Hi. The following series of three patches provides some
improvements and bug fixes to DRI2 swap scheduling, kms pageflipping and
pageflip completion timestamping. And a fix for desktop corruption
when switching between redirected and unredirected fullscreen windows.

These are mostly direct translations of similar functionality and bug-fixes
from the intel ddx and ati ddx. All successfully tested on a GeForce-7800
GTX and QuadroFX-570 in single display mode and dual-display modes (xinerama
desktop spanning and clone mode).

I'll send another separate patch for the Linux nouveau-kms driver's pageflip
completion routine, so it reports back proper pageflip completion events
with correct timestamp and vblank count (according to OML_sync_control spec).

Lucas Stach has an almost finished patch for the nouveau-kms driver to implement
the drm high-precision vblank timestamping hook. All patches taken together
were tested on NV-47 with high precision measurement equipment. Results show
that the pageflip completion timestamps reported with these patches are accurate
with respect to reality, with a residual error of less than 40 microseconds.

Please review and apply as you see fit.

thanks,
-mario

[PATCH 1/3] dri2: Implement handling of pageflip completion events.

[Mario Kleiner]

Requests pageflip completion events from the kernel.
Implements pageflip completion handler to finalize
and timestamp swaps.

Completion handler includes a consistency check, and
disambiguation if multiple crtc's are involved in a
pageflip (e.g., clone mode, extendend desktop). Only
the timestamp of the crtc whose vblank event initially
triggered the swap is used, but handler waits for flip
completion on all involved crtc's before completing the
swap and releasing the old framebuffer.

This code is almost identical to the code used in the
ati/radeon ddx and intel ddx.

Signed-off-by: Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org>
---
 src/drmmode_display.c |  105 +++++++++++++++++++++++++++++++++++++++++++++++--
 src/nouveau_dri2.c    |   89 +++++++++++++++++++++++++++++++++++++++--
 src/nv_proto.h        |    5 ++-
 3 files changed, 189 insertions(+), 10 deletions(-)

diff --git a/src/drmmode_display.c b/src/drmmode_display.c
index 3afef66..bcb2a94 100644
--- a/src/drmmode_display.c
+++ b/src/drmmode_display.c
@@ -83,6 +83,21 @@ typedef struct {
     drmmode_prop_ptr props;
 } drmmode_output_private_rec, *drmmode_output_private_ptr;
 
+typedef struct {
+    drmmode_ptr drmmode;
+    unsigned old_fb_id;
+    int flip_count;
+    void *event_data;
+    unsigned int fe_frame;
+    unsigned int fe_tv_sec;
+    unsigned int fe_tv_usec;
+} drmmode_flipdata_rec, *drmmode_flipdata_ptr;
+
+typedef struct {
+    drmmode_flipdata_ptr flipdata;
+    Bool dispatch_me;
+} drmmode_flipevtcarrier_rec, *drmmode_flipevtcarrier_ptr;
+
 static void drmmode_output_dpms(xf86OutputPtr output, int mode);
 
 static drmmode_ptr
@@ -1246,13 +1261,17 @@ drmmode_cursor_init(ScreenPtr pScreen)
 }
 
 Bool
-drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv)
+drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv,
+		  unsigned int ref_crtc_hw_id)
 {
 	ScrnInfoPtr scrn = xf86Screens[draw->pScreen->myNum];
 	xf86CrtcConfigPtr config = XF86_CRTC_CONFIG_PTR(scrn);
 	drmmode_crtc_private_ptr crtc = config->crtc[0]->driver_private;
 	drmmode_ptr mode = crtc->drmmode;
 	int ret, i, old_fb_id;
+	int emitted = 0;
+	drmmode_flipdata_ptr flipdata;
+	drmmode_flipevtcarrier_ptr flipcarrier;
 
 	old_fb_id = mode->fb_id;
 	ret = drmModeAddFB(mode->fd, scrn->virtualX, scrn->virtualY,
@@ -1265,24 +1284,64 @@ drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv)
 		return FALSE;
 	}
 
+	flipdata = calloc(1, sizeof(drmmode_flipdata_rec));
+	if (!flipdata) {
+		xf86DrvMsg(scrn->scrnIndex, X_WARNING,
+		"flip queue: data alloc failed.\n");
+		goto error_undo;
+	}
+
+	flipdata->event_data = priv;
+	flipdata->drmmode = mode;
+
 	for (i = 0; i < config->num_crtc; i++) {
 		crtc = config->crtc[i]->driver_private;
 
 		if (!config->crtc[i]->enabled)
 			continue;
 
+		flipdata->flip_count++;
+
+		flipcarrier = calloc(1, sizeof(drmmode_flipevtcarrier_rec));
+		if (!flipcarrier) {
+			xf86DrvMsg(scrn->scrnIndex, X_WARNING,
+				   "flip queue: carrier alloc failed.\n");
+			if (emitted == 0)
+				free(flipdata);
+			goto error_undo;
+		}
+
+		/* Only the reference crtc will finally deliver its page flip
+		 * completion event. All other crtc's events will be discarded.
+		 */
+		flipcarrier->dispatch_me = ((1 << i) == ref_crtc_hw_id);
+		flipcarrier->flipdata = flipdata;
+
 		ret = drmModePageFlip(mode->fd, crtc->mode_crtc->crtc_id,
-				      mode->fb_id, 0, priv);
+				      mode->fb_id, DRM_MODE_PAGE_FLIP_EVENT,
+				      flipcarrier);
 		if (ret) {
 			xf86DrvMsg(scrn->scrnIndex, X_WARNING,
 				   "flip queue failed: %s\n", strerror(errno));
-			return FALSE;
+
+			free(flipcarrier);
+			if (emitted == 0)
+				free(flipdata);
+			goto error_undo;
 		}
+
+		emitted++;
 	}
 
-	drmModeRmFB(mode->fd, old_fb_id);
+	/* Will release old fb after all crtc's completed flip. */
+	flipdata->old_fb_id = old_fb_id;
 
 	return TRUE;
+
+error_undo:
+	drmModeRmFB(mode->fd, mode->fb_id);
+	mode->fb_id = old_fb_id;
+	return FALSE;
 }
 
 #ifdef HAVE_LIBUDEV
@@ -1348,6 +1407,40 @@ drmmode_uevent_fini(ScrnInfoPtr scrn)
 }
 
 static void
+drmmode_flip_handler(int fd, unsigned int frame, unsigned int tv_sec,
+		     unsigned int tv_usec, void *event_data)
+{
+	drmmode_flipevtcarrier_ptr flipcarrier = event_data;
+	drmmode_flipdata_ptr flipdata = flipcarrier->flipdata;
+	drmmode_ptr drmmode = flipdata->drmmode;
+
+	/* Is this the event whose info shall be delivered to higher level? */
+	if (flipcarrier->dispatch_me) {
+		/* Yes: Cache msc, ust for later delivery. */
+		flipdata->fe_frame = frame;
+		flipdata->fe_tv_sec = tv_sec;
+		flipdata->fe_tv_usec = tv_usec;
+	}
+	free(flipcarrier);
+
+	/* Last crtc completed flip? */
+	flipdata->flip_count--;
+	if (flipdata->flip_count > 0)
+		return;
+
+	/* Release framebuffer */
+	drmModeRmFB(drmmode->fd, flipdata->old_fb_id);
+
+	if (flipdata->event_data == NULL)
+		return;
+
+	/* Deliver cached msc, ust from reference crtc to flip event handler */
+	nouveau_dri2_flip_event_handler(flipdata->fe_frame, flipdata->fe_tv_sec,
+					flipdata->fe_tv_usec, flipdata->event_data);
+	free(flipdata);
+}
+
+static void
 drmmode_wakeup_handler(pointer data, int err, pointer p)
 {
 	ScrnInfoPtr scrn = data;
@@ -1377,6 +1470,10 @@ drmmode_screen_init(ScreenPtr pScreen)
 	/* Plug in a vblank event handler */
 	drmmode->event_context.version = DRM_EVENT_CONTEXT_VERSION;
 	drmmode->event_context.vblank_handler = nouveau_dri2_vblank_handler;
+
+	/* Plug in a pageflip completion event handler */
+	drmmode->event_context.page_flip_handler = drmmode_flip_handler;
+
 	AddGeneralSocket(drmmode->fd);
 
 	/* Register a wakeup handler to get informed on DRM events */
diff --git a/src/nouveau_dri2.c b/src/nouveau_dri2.c
index 1a68ed3..87eaf08 100644
--- a/src/nouveau_dri2.c
+++ b/src/nouveau_dri2.c
@@ -136,6 +136,7 @@ struct nouveau_dri2_vblank_state {
 	DRI2BufferPtr src;
 	DRI2SwapEventPtr func;
 	void *data;
+	unsigned int frame;
 };
 
 static Bool
@@ -222,6 +223,18 @@ nouveau_dri2_finish_swap(DrawablePtr draw, unsigned int frame,
 	REGION_INIT(0, &reg, (&(BoxRec){ 0, 0, draw->width, draw->height }), 0);
 	REGION_TRANSLATE(0, &reg, draw->x, draw->y);
 
+	/* Main crtc for this drawable shall finally deliver pageflip event. */
+	unsigned int ref_crtc_hw_id = nv_window_belongs_to_crtc(scrn, draw->x,
+								draw->y,
+								draw->width,
+								draw->height);
+
+	/* Whenever first crtc is involved, choose it as reference, as
+	 * its vblank event triggered this swap.
+	 */
+	if (ref_crtc_hw_id & 1)
+		ref_crtc_hw_id = 1;
+
 	/* Throttle on the previous frame before swapping */
 	nouveau_bo_map(dst_bo, NOUVEAU_BO_RD);
 	nouveau_bo_unmap(dst_bo);
@@ -246,7 +259,7 @@ nouveau_dri2_finish_swap(DrawablePtr draw, unsigned int frame,
 
 		if (DRI2CanFlip(draw)) {
 			type = DRI2_FLIP_COMPLETE;
-			ret = drmmode_page_flip(draw, src_pix, s);
+			ret = drmmode_page_flip(draw, src_pix, s, ref_crtc_hw_id);
 			if (!ret)
 				goto out;
 		}
@@ -255,6 +268,10 @@ nouveau_dri2_finish_swap(DrawablePtr draw, unsigned int frame,
 		SWAP(nouveau_pixmap(dst_pix)->bo, nouveau_pixmap(src_pix)->bo);
 
 		DamageRegionProcessPending(draw);
+
+		/* If it is a page flip, finish it in the flip event handler. */
+		if (type == DRI2_FLIP_COMPLETE)
+			return;
 	} else {
 		type = DRI2_BLIT_COMPLETE;
 
@@ -289,7 +306,7 @@ nouveau_dri2_schedule_swap(ClientPtr client, DrawablePtr draw,
 			   DRI2SwapEventPtr func, void *data)
 {
 	struct nouveau_dri2_vblank_state *s;
-	CARD64 current_msc;
+	CARD64 current_msc, expect_msc;
 	int ret;
 
 	/* Initialize a swap structure */
@@ -298,7 +315,7 @@ nouveau_dri2_schedule_swap(ClientPtr client, DrawablePtr draw,
 		return FALSE;
 
 	*s = (struct nouveau_dri2_vblank_state)
-		{ SWAP, client, draw->id, dst, src, func, data };
+		{ SWAP, client, draw->id, dst, src, func, data, 0 };
 
 	if (can_sync_to_vblank(draw)) {
 		/* Get current sequence */
@@ -316,10 +333,10 @@ nouveau_dri2_schedule_swap(ClientPtr client, DrawablePtr draw,
 		ret = nouveau_wait_vblank(draw, DRM_VBLANK_ABSOLUTE |
 					  DRM_VBLANK_EVENT,
 					  max(current_msc, *target_msc - 1),
-					  NULL, NULL, s);
+					  &expect_msc, NULL, s);
 		if (ret)
 			goto fail;
-
+		s->frame = (unsigned int) expect_msc & 0xffffffff;
 	} else {
 		/* We can't/don't want to sync to vblank, just swap. */
 		nouveau_dri2_finish_swap(draw, 0, 0, 0, s);
@@ -423,6 +440,68 @@ nouveau_dri2_vblank_handler(int fd, unsigned int frame,
 	}
 }
 
+void
+nouveau_dri2_flip_event_handler(unsigned int frame, unsigned int tv_sec,
+				unsigned int tv_usec, void *event_data)
+{
+	struct nouveau_dri2_vblank_state *flip = event_data;
+	DrawablePtr draw;
+	ScreenPtr screen;
+	ScrnInfoPtr scrn;
+	int status;
+	PixmapPtr pixmap;
+
+	status = dixLookupDrawable(&draw, flip->draw, serverClient,
+				   M_ANY, DixWriteAccess);
+	if (status != Success) {
+		free(flip);
+		return;
+	}
+
+	screen = draw->pScreen;
+	scrn = xf86Screens[screen->myNum];
+
+	pixmap = screen->GetScreenPixmap(screen);
+	xf86DrvMsg(scrn->scrnIndex, X_INFO,
+		   "%s:%d fevent[%p] width %d pitch %d (/4 %d)\n",
+		   __func__, __LINE__, flip, pixmap->drawable.width,
+		   pixmap->devKind, pixmap->devKind/4);
+
+	/* We assume our flips arrive in order, so we don't check the frame */
+	switch (flip->action) {
+	case SWAP:
+		/* Check for too small vblank count of pageflip completion,
+		 * taking wraparound into account. This usually means some
+		 * defective kms pageflip completion, causing wrong (msc, ust)
+		 * return values and possible visual corruption.
+		 * Skip test for frame == 0, as this is a valid constant value
+		 * reported by all Linux kernels at least up to Linux 3.0.
+		 */
+		if ((frame != 0) &&
+		    (frame < flip->frame) && (flip->frame - frame < 5)) {
+			xf86DrvMsg(scrn->scrnIndex, X_WARNING,
+				   "%s: Pageflip has impossible msc %d < target_msc %d\n",
+				   __func__, frame, flip->frame);
+			/* All-Zero values signal failure of (msc, ust)
+			 * timestamping to client.
+			 */
+			frame = tv_sec = tv_usec = 0;
+		}
+
+		DRI2SwapComplete(flip->client, draw, frame, tv_sec, tv_usec,
+				 DRI2_FLIP_COMPLETE, flip->func,
+				 flip->data);
+		break;
+	default:
+		xf86DrvMsg(scrn->scrnIndex, X_WARNING,
+			   "%s: unknown vblank event received\n", __func__);
+		/* Unknown type */
+		break;
+	}
+
+	free(flip);
+}
+
 Bool
 nouveau_dri2_init(ScreenPtr pScreen)
 {
diff --git a/src/nv_proto.h b/src/nv_proto.h
index 2e4fce0..2bd2ac7 100644
--- a/src/nv_proto.h
+++ b/src/nv_proto.h
@@ -7,7 +7,8 @@ void drmmode_adjust_frame(ScrnInfoPtr pScrn, int x, int y, int flags);
 void drmmode_remove_fb(ScrnInfoPtr pScrn);
 Bool drmmode_cursor_init(ScreenPtr pScreen);
 void drmmode_fbcon_copy(ScreenPtr pScreen);
-Bool drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv);
+Bool drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv,
+		       unsigned int ref_crtc_hw_id);
 void drmmode_screen_init(ScreenPtr pScreen);
 void drmmode_screen_fini(ScreenPtr pScreen);
 
@@ -26,6 +27,8 @@ Bool nouveau_allocate_surface(ScrnInfoPtr scrn, int width, int height,
 void nouveau_dri2_vblank_handler(int fd, unsigned int frame,
 				 unsigned int tv_sec, unsigned int tv_usec,
 				 void *event_data);
+void nouveau_dri2_flip_event_handler(unsigned int frame, unsigned int tv_sec,
+				     unsigned int tv_usec, void *event_data);
 Bool nouveau_dri2_init(ScreenPtr pScreen);
 void nouveau_dri2_fini(ScreenPtr pScreen);
 
-- 
1.7.1

Re: [PATCH 1/3] dri2: Implement handling of pageflip completion events.

[Francisco Jerez]

[-- Attachment #1.1.1: Type: text/plain, Size: 13879 bytes --]

Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org> writes:

> Requests pageflip completion events from the kernel.
> Implements pageflip completion handler to finalize
> and timestamp swaps.
>
> Completion handler includes a consistency check, and
> disambiguation if multiple crtc's are involved in a
> pageflip (e.g., clone mode, extendend desktop). Only
> the timestamp of the crtc whose vblank event initially
> triggered the swap is used, but handler waits for flip
> completion on all involved crtc's before completing the
> swap and releasing the old framebuffer.
>
> This code is almost identical to the code used in the
> ati/radeon ddx and intel ddx.
>
There's a good reason that I held myself back from doing this when I
wrote the rest of the SwapBuffers stuff; right now the X server assumes
that the DDX can't handle more than one SwapBuffers request in flight at
any given time, so, after a SwapBuffers request has been received, the
client is prevented from doing anything until the swap (and,
consequently, the whole rendering of the previous frame) has been
completed, that means that the client is forced to render each frame in
lock-step, and it leads to a considerable performance loss.

In my judgment it seemed quite dumb to wire up all the page-flipping
infrastructure together, only to notice that it was slowing things down
even further (since performance was the main point I had for it...). As
the ability to report accurate swap completion events seemed to be of
comparatively limited usefulness, I made the DDX pretend the buffers are
swapped one frame before they actually are as a temporary workaround
(see the comment at the end of nouveau_dri2_finish_swap()).

So, IMHO, this change depends on the X server N-buffering changes going
in - actually the DRI2SwapLimit() API that (IIRC) Pauli Nieminen
proposed some time ago was all we needed, but it hasn't been accepted
upstream for some reason.

> Signed-off-by: Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org>
> ---
>  src/drmmode_display.c |  105 +++++++++++++++++++++++++++++++++++++++++++++++--
>  src/nouveau_dri2.c    |   89 +++++++++++++++++++++++++++++++++++++++--
>  src/nv_proto.h        |    5 ++-
>  3 files changed, 189 insertions(+), 10 deletions(-)
>
> diff --git a/src/drmmode_display.c b/src/drmmode_display.c
> index 3afef66..bcb2a94 100644
> --- a/src/drmmode_display.c
> +++ b/src/drmmode_display.c
> @@ -83,6 +83,21 @@ typedef struct {
>      drmmode_prop_ptr props;
>  } drmmode_output_private_rec, *drmmode_output_private_ptr;
>  
> +typedef struct {
> +    drmmode_ptr drmmode;
> +    unsigned old_fb_id;
> +    int flip_count;
> +    void *event_data;
> +    unsigned int fe_frame;
> +    unsigned int fe_tv_sec;
> +    unsigned int fe_tv_usec;
> +} drmmode_flipdata_rec, *drmmode_flipdata_ptr;
> +
> +typedef struct {
> +    drmmode_flipdata_ptr flipdata;
> +    Bool dispatch_me;
> +} drmmode_flipevtcarrier_rec, *drmmode_flipevtcarrier_ptr;
> +
>  static void drmmode_output_dpms(xf86OutputPtr output, int mode);
>  
>  static drmmode_ptr
> @@ -1246,13 +1261,17 @@ drmmode_cursor_init(ScreenPtr pScreen)
>  }
>  
>  Bool
> -drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv)
> +drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv,
> +		  unsigned int ref_crtc_hw_id)
>  {
>  	ScrnInfoPtr scrn = xf86Screens[draw->pScreen->myNum];
>  	xf86CrtcConfigPtr config = XF86_CRTC_CONFIG_PTR(scrn);
>  	drmmode_crtc_private_ptr crtc = config->crtc[0]->driver_private;
>  	drmmode_ptr mode = crtc->drmmode;
>  	int ret, i, old_fb_id;
> +	int emitted = 0;
> +	drmmode_flipdata_ptr flipdata;
> +	drmmode_flipevtcarrier_ptr flipcarrier;
>  
>  	old_fb_id = mode->fb_id;
>  	ret = drmModeAddFB(mode->fd, scrn->virtualX, scrn->virtualY,
> @@ -1265,24 +1284,64 @@ drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv)
>  		return FALSE;
>  	}
>  
> +	flipdata = calloc(1, sizeof(drmmode_flipdata_rec));
> +	if (!flipdata) {
> +		xf86DrvMsg(scrn->scrnIndex, X_WARNING,
> +		"flip queue: data alloc failed.\n");
> +		goto error_undo;
> +	}
> +
> +	flipdata->event_data = priv;
> +	flipdata->drmmode = mode;
> +
>  	for (i = 0; i < config->num_crtc; i++) {
>  		crtc = config->crtc[i]->driver_private;
>  
>  		if (!config->crtc[i]->enabled)
>  			continue;
>  
> +		flipdata->flip_count++;
> +
> +		flipcarrier = calloc(1, sizeof(drmmode_flipevtcarrier_rec));
> +		if (!flipcarrier) {
> +			xf86DrvMsg(scrn->scrnIndex, X_WARNING,
> +				   "flip queue: carrier alloc failed.\n");
> +			if (emitted == 0)
> +				free(flipdata);
> +			goto error_undo;
> +		}
> +
> +		/* Only the reference crtc will finally deliver its page flip
> +		 * completion event. All other crtc's events will be discarded.
> +		 */
> +		flipcarrier->dispatch_me = ((1 << i) == ref_crtc_hw_id);
> +		flipcarrier->flipdata = flipdata;
> +
>  		ret = drmModePageFlip(mode->fd, crtc->mode_crtc->crtc_id,
> -				      mode->fb_id, 0, priv);
> +				      mode->fb_id, DRM_MODE_PAGE_FLIP_EVENT,
> +				      flipcarrier);
>  		if (ret) {
>  			xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>  				   "flip queue failed: %s\n", strerror(errno));
> -			return FALSE;
> +
> +			free(flipcarrier);
> +			if (emitted == 0)
> +				free(flipdata);
> +			goto error_undo;
>  		}
> +
> +		emitted++;
>  	}
>  
> -	drmModeRmFB(mode->fd, old_fb_id);
> +	/* Will release old fb after all crtc's completed flip. */
> +	flipdata->old_fb_id = old_fb_id;
>  
>  	return TRUE;
> +
> +error_undo:
> +	drmModeRmFB(mode->fd, mode->fb_id);
> +	mode->fb_id = old_fb_id;
> +	return FALSE;
>  }
>  
>  #ifdef HAVE_LIBUDEV
> @@ -1348,6 +1407,40 @@ drmmode_uevent_fini(ScrnInfoPtr scrn)
>  }
>  
>  static void
> +drmmode_flip_handler(int fd, unsigned int frame, unsigned int tv_sec,
> +		     unsigned int tv_usec, void *event_data)
> +{
> +	drmmode_flipevtcarrier_ptr flipcarrier = event_data;
> +	drmmode_flipdata_ptr flipdata = flipcarrier->flipdata;
> +	drmmode_ptr drmmode = flipdata->drmmode;
> +
> +	/* Is this the event whose info shall be delivered to higher level? */
> +	if (flipcarrier->dispatch_me) {
> +		/* Yes: Cache msc, ust for later delivery. */
> +		flipdata->fe_frame = frame;
> +		flipdata->fe_tv_sec = tv_sec;
> +		flipdata->fe_tv_usec = tv_usec;
> +	}
> +	free(flipcarrier);
> +
> +	/* Last crtc completed flip? */
> +	flipdata->flip_count--;
> +	if (flipdata->flip_count > 0)
> +		return;
> +
> +	/* Release framebuffer */
> +	drmModeRmFB(drmmode->fd, flipdata->old_fb_id);
> +
> +	if (flipdata->event_data == NULL)
> +		return;
> +
> +	/* Deliver cached msc, ust from reference crtc to flip event handler */
> +	nouveau_dri2_flip_event_handler(flipdata->fe_frame, flipdata->fe_tv_sec,
> +					flipdata->fe_tv_usec, flipdata->event_data);
> +	free(flipdata);
> +}
> +
> +static void
>  drmmode_wakeup_handler(pointer data, int err, pointer p)
>  {
>  	ScrnInfoPtr scrn = data;
> @@ -1377,6 +1470,10 @@ drmmode_screen_init(ScreenPtr pScreen)
>  	/* Plug in a vblank event handler */
>  	drmmode->event_context.version = DRM_EVENT_CONTEXT_VERSION;
>  	drmmode->event_context.vblank_handler = nouveau_dri2_vblank_handler;
> +
> +	/* Plug in a pageflip completion event handler */
> +	drmmode->event_context.page_flip_handler = drmmode_flip_handler;
> +
>  	AddGeneralSocket(drmmode->fd);
>  
>  	/* Register a wakeup handler to get informed on DRM events */
> diff --git a/src/nouveau_dri2.c b/src/nouveau_dri2.c
> index 1a68ed3..87eaf08 100644
> --- a/src/nouveau_dri2.c
> +++ b/src/nouveau_dri2.c
> @@ -136,6 +136,7 @@ struct nouveau_dri2_vblank_state {
>  	DRI2BufferPtr src;
>  	DRI2SwapEventPtr func;
>  	void *data;
> +	unsigned int frame;
>  };
>  
>  static Bool
> @@ -222,6 +223,18 @@ nouveau_dri2_finish_swap(DrawablePtr draw, unsigned int frame,
>  	REGION_INIT(0, &reg, (&(BoxRec){ 0, 0, draw->width, draw->height }), 0);
>  	REGION_TRANSLATE(0, &reg, draw->x, draw->y);
>  
> +	/* Main crtc for this drawable shall finally deliver pageflip event. */
> +	unsigned int ref_crtc_hw_id = nv_window_belongs_to_crtc(scrn, draw->x,
> +								draw->y,
> +								draw->width,
> +								draw->height);
> +
> +	/* Whenever first crtc is involved, choose it as reference, as
> +	 * its vblank event triggered this swap.
> +	 */
> +	if (ref_crtc_hw_id & 1)
> +		ref_crtc_hw_id = 1;
> +
>  	/* Throttle on the previous frame before swapping */
>  	nouveau_bo_map(dst_bo, NOUVEAU_BO_RD);
>  	nouveau_bo_unmap(dst_bo);
> @@ -246,7 +259,7 @@ nouveau_dri2_finish_swap(DrawablePtr draw, unsigned int frame,
>  
>  		if (DRI2CanFlip(draw)) {
>  			type = DRI2_FLIP_COMPLETE;
> -			ret = drmmode_page_flip(draw, src_pix, s);
> +			ret = drmmode_page_flip(draw, src_pix, s, ref_crtc_hw_id);
>  			if (!ret)
>  				goto out;
>  		}
> @@ -255,6 +268,10 @@ nouveau_dri2_finish_swap(DrawablePtr draw, unsigned int frame,
>  		SWAP(nouveau_pixmap(dst_pix)->bo, nouveau_pixmap(src_pix)->bo);
>  
>  		DamageRegionProcessPending(draw);
> +
> +		/* If it is a page flip, finish it in the flip event handler. */
> +		if (type == DRI2_FLIP_COMPLETE)
> +			return;
>  	} else {
>  		type = DRI2_BLIT_COMPLETE;
>  
> @@ -289,7 +306,7 @@ nouveau_dri2_schedule_swap(ClientPtr client, DrawablePtr draw,
>  			   DRI2SwapEventPtr func, void *data)
>  {
>  	struct nouveau_dri2_vblank_state *s;
> -	CARD64 current_msc;
> +	CARD64 current_msc, expect_msc;
>  	int ret;
>  
>  	/* Initialize a swap structure */
> @@ -298,7 +315,7 @@ nouveau_dri2_schedule_swap(ClientPtr client, DrawablePtr draw,
>  		return FALSE;
>  
>  	*s = (struct nouveau_dri2_vblank_state)
> -		{ SWAP, client, draw->id, dst, src, func, data };
> +		{ SWAP, client, draw->id, dst, src, func, data, 0 };
>  
>  	if (can_sync_to_vblank(draw)) {
>  		/* Get current sequence */
> @@ -316,10 +333,10 @@ nouveau_dri2_schedule_swap(ClientPtr client, DrawablePtr draw,
>  		ret = nouveau_wait_vblank(draw, DRM_VBLANK_ABSOLUTE |
>  					  DRM_VBLANK_EVENT,
>  					  max(current_msc, *target_msc - 1),
> -					  NULL, NULL, s);
> +					  &expect_msc, NULL, s);
>  		if (ret)
>  			goto fail;
> -
> +		s->frame = (unsigned int) expect_msc & 0xffffffff;
>  	} else {
>  		/* We can't/don't want to sync to vblank, just swap. */
>  		nouveau_dri2_finish_swap(draw, 0, 0, 0, s);
> @@ -423,6 +440,68 @@ nouveau_dri2_vblank_handler(int fd, unsigned int frame,
>  	}
>  }
>  
> +void
> +nouveau_dri2_flip_event_handler(unsigned int frame, unsigned int tv_sec,
> +				unsigned int tv_usec, void *event_data)
> +{
> +	struct nouveau_dri2_vblank_state *flip = event_data;
> +	DrawablePtr draw;
> +	ScreenPtr screen;
> +	ScrnInfoPtr scrn;
> +	int status;
> +	PixmapPtr pixmap;
> +
> +	status = dixLookupDrawable(&draw, flip->draw, serverClient,
> +				   M_ANY, DixWriteAccess);
> +	if (status != Success) {
> +		free(flip);
> +		return;
> +	}
> +
> +	screen = draw->pScreen;
> +	scrn = xf86Screens[screen->myNum];
> +
> +	pixmap = screen->GetScreenPixmap(screen);
> +	xf86DrvMsg(scrn->scrnIndex, X_INFO,
> +		   "%s:%d fevent[%p] width %d pitch %d (/4 %d)\n",
> +		   __func__, __LINE__, flip, pixmap->drawable.width,
> +		   pixmap->devKind, pixmap->devKind/4);
> +
> +	/* We assume our flips arrive in order, so we don't check the frame */
> +	switch (flip->action) {
> +	case SWAP:
> +		/* Check for too small vblank count of pageflip completion,
> +		 * taking wraparound into account. This usually means some
> +		 * defective kms pageflip completion, causing wrong (msc, ust)
> +		 * return values and possible visual corruption.
> +		 * Skip test for frame == 0, as this is a valid constant value
> +		 * reported by all Linux kernels at least up to Linux 3.0.
> +		 */
> +		if ((frame != 0) &&
> +		    (frame < flip->frame) && (flip->frame - frame < 5)) {
> +			xf86DrvMsg(scrn->scrnIndex, X_WARNING,
> +				   "%s: Pageflip has impossible msc %d < target_msc %d\n",
> +				   __func__, frame, flip->frame);
> +			/* All-Zero values signal failure of (msc, ust)
> +			 * timestamping to client.
> +			 */
> +			frame = tv_sec = tv_usec = 0;
> +		}
> +
> +		DRI2SwapComplete(flip->client, draw, frame, tv_sec, tv_usec,
> +				 DRI2_FLIP_COMPLETE, flip->func,
> +				 flip->data);
> +		break;
> +	default:
> +		xf86DrvMsg(scrn->scrnIndex, X_WARNING,
> +			   "%s: unknown vblank event received\n", __func__);
> +		/* Unknown type */
> +		break;
> +	}
> +
> +	free(flip);
> +}
> +
>  Bool
>  nouveau_dri2_init(ScreenPtr pScreen)
>  {
> diff --git a/src/nv_proto.h b/src/nv_proto.h
> index 2e4fce0..2bd2ac7 100644
> --- a/src/nv_proto.h
> +++ b/src/nv_proto.h
> @@ -7,7 +7,8 @@ void drmmode_adjust_frame(ScrnInfoPtr pScrn, int x, int y, int flags);
>  void drmmode_remove_fb(ScrnInfoPtr pScrn);
>  Bool drmmode_cursor_init(ScreenPtr pScreen);
>  void drmmode_fbcon_copy(ScreenPtr pScreen);
> -Bool drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv);
> +Bool drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv,
> +		       unsigned int ref_crtc_hw_id);
>  void drmmode_screen_init(ScreenPtr pScreen);
>  void drmmode_screen_fini(ScreenPtr pScreen);
>  
> @@ -26,6 +27,8 @@ Bool nouveau_allocate_surface(ScrnInfoPtr scrn, int width, int height,
>  void nouveau_dri2_vblank_handler(int fd, unsigned int frame,
>  				 unsigned int tv_sec, unsigned int tv_usec,
>  				 void *event_data);
> +void nouveau_dri2_flip_event_handler(unsigned int frame, unsigned int tv_sec,
> +				     unsigned int tv_usec, void *event_data);
>  Bool nouveau_dri2_init(ScreenPtr pScreen);
>  void nouveau_dri2_fini(ScreenPtr pScreen);

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Re: [PATCH 1/3] dri2: Implement handling of pageflip completion events.

[Mario Kleiner]

On Sep 8, 2011, at 12:45 AM, Francisco Jerez wrote:

> Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org> writes:
>
>> Requests pageflip completion events from the kernel.
>> Implements pageflip completion handler to finalize
>> and timestamp swaps.
>>
>> Completion handler includes a consistency check, and
>> disambiguation if multiple crtc's are involved in a
>> pageflip (e.g., clone mode, extendend desktop). Only
>> the timestamp of the crtc whose vblank event initially
>> triggered the swap is used, but handler waits for flip
>> completion on all involved crtc's before completing the
>> swap and releasing the old framebuffer.
>>
>> This code is almost identical to the code used in the
>> ati/radeon ddx and intel ddx.
>>
> There's a good reason that I held myself back from doing this when I
> wrote the rest of the SwapBuffers stuff; right now the X server  
> assumes
> that the DDX can't handle more than one SwapBuffers request in  
> flight at
> any given time, so, after a SwapBuffers request has been received, the
> client is prevented from doing anything until the swap (and,
> consequently, the whole rendering of the previous frame) has been
> completed, that means that the client is forced to render each  
> frame in
> lock-step, and it leads to a considerable performance loss.
>
> In my judgment it seemed quite dumb to wire up all the page-flipping
> infrastructure together, only to notice that it was slowing things  
> down
> even further (since performance was the main point I had for  
> it...). As
> the ability to report accurate swap completion events seemed to be of
> comparatively limited usefulness, I made the DDX pretend the  
> buffers are
> swapped one frame before they actually are as a temporary workaround
> (see the comment at the end of nouveau_dri2_finish_swap()).
>

Hi, thanks for the comments.

I see your point, but at least as a starting point for the first  
iteration i don't think the current dri2 implementation of pageflips  
was a dumb decision.

It is the same default "double buffer" behaviour that the binary  
drivers on Linux and also on other os'es (OS/X and Windows) expose.  
As a default i think it makes sense if an application wants tight  
control over presentation timing or - in the case of games - wants to  
prevent irritating lag between user input and visual updates -- limit  
the number of frames that the game can prerender.

On the intel and ati gpu's, purely double-buffered pageflipping is  
already a win for conserving memory bandwidth and because you avoid  
blocking the single command fifo for multiple rendering clients, as  
you have to if you use vsync'ed copy-blits to avoid tearing. This may  
be less of a win on nvidia because they have multiple fifo's or some  
independent dma engines if i understand correctly?

Anyway, it's better for performance if clients can queue up multiple  
rendered frames for other non-interactive use cases, e.g., benchmarks  
or graphics demos. Or if client apps can decide themselves about  
presentation timing. That was the point of support for the  
oml_sync_control and intel_swap_events extensions and all the  
timestamping.

My specific use case for this patchset is a popular free software  
toolkit (http://www.psychtoolbox.org) used by neuro-scientists and  
brain scientists in general for audio & visual stimulus presentation,  
i/o etc. . Nouveau in its current state, at least on the cards i  
tested, would be already a very suitable solution for doing this on  
linux+nvidia.

The only missing "must-have" feature for such applications are very  
reliable and accurate presentation timestamps. Having those puts  
nouveau ahead of the binary blob for such apps. The workloads are  
usually not as demanding as current games and an occassional skipped  
frame is tolerable, but frequently getting wrong/misleading  
timestamps of when a frame was presented would be a total show- 
stopper. Currently i have to blacklist nouveau in my toolkit just for  
that reason.

> So, IMHO, this change depends on the X server N-buffering changes  
> going
> in - actually the DRI2SwapLimit() API that (IIRC) Pauli Nieminen
> proposed some time ago was all we needed, but it hasn't been accepted
> upstream for some reason.
>

I was involved in that discussion at the time, iirc. I think having  
the DRI2SwapLimit() API would make a lot of sense as a first step and  
that those patches just got dropped due to maintainer-overload, not  
really too much for technical reasons. To do multi-buffering  
correctly, as specified by the oml_sync_control spec, a bit more than  
Paul's API for setting the swap_limit would be needed, either on the  
ddx driver level or in the x-server itself, e.g., to make sure the  
ordering of glXSwapBuffersMscOML() swaps is correct, no more than one  
swap gets executed per video refresh and to satisfy the divisor/ 
remainder constraints correctly if they are used by a client. Special  
cases which are not important for typical games or benchmarks but  
important for toolkits with precise timing needs. I actually wanted  
to work on that, but didn't get around to do it so far. First i'd  
like to have nouveau at the same level of timing functionality as ati  
and intel.

Could we have an optional nouveau-ddx xorg.conf parameter to select  
between the current codepath and the "lower-performance but correct  
timestamping" path implemented in these patches? Something like  
"EnableTriplebuffering" or "Swaplimit" or  
"MaxNumberPrerenderedFrames"? I think having such a setting would  
make sense anyway, even if Paul's API is implemented, exactly to  
control things like max number of prerendered frames for games and  
apps which only use glXSwapBuffers() but should have some control  
over input lag.

The latest intel ddx seems to do the same with a "Triplebuffering"  
setting.

The setting could default to your current performance implementation.  
The path in the new patches would get pretty frequent exercise &  
testing by myself and currently a couple of hundred happy neuro- 
scientists.

thanks,
-mario

>> Signed-off-by: Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org>
>> ---
>>  src/drmmode_display.c |  105 +++++++++++++++++++++++++++++++++++++ 
>> ++++++++++--
>>  src/nouveau_dri2.c    |   89 +++++++++++++++++++++++++++++++++++++ 
>> ++--
>>  src/nv_proto.h        |    5 ++-
>>  3 files changed, 189 insertions(+), 10 deletions(-)
>>
>> diff --git a/src/drmmode_display.c b/src/drmmode_display.c
>> index 3afef66..bcb2a94 100644
>> --- a/src/drmmode_display.c
>> +++ b/src/drmmode_display.c
>> @@ -83,6 +83,21 @@ typedef struct {
>>      drmmode_prop_ptr props;
>>  } drmmode_output_private_rec, *drmmode_output_private_ptr;
>>
>> +typedef struct {
>> +    drmmode_ptr drmmode;
>> +    unsigned old_fb_id;
>> +    int flip_count;
>> +    void *event_data;
>> +    unsigned int fe_frame;
>> +    unsigned int fe_tv_sec;
>> +    unsigned int fe_tv_usec;
>> +} drmmode_flipdata_rec, *drmmode_flipdata_ptr;
>> +
>> +typedef struct {
>> +    drmmode_flipdata_ptr flipdata;
>> +    Bool dispatch_me;
>> +} drmmode_flipevtcarrier_rec, *drmmode_flipevtcarrier_ptr;
>> +
>>  static void drmmode_output_dpms(xf86OutputPtr output, int mode);
>>
>>  static drmmode_ptr
>> @@ -1246,13 +1261,17 @@ drmmode_cursor_init(ScreenPtr pScreen)
>>  }
>>
>>  Bool
>> -drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv)
>> +drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv,
>> +		  unsigned int ref_crtc_hw_id)
>>  {
>>  	ScrnInfoPtr scrn = xf86Screens[draw->pScreen->myNum];
>>  	xf86CrtcConfigPtr config = XF86_CRTC_CONFIG_PTR(scrn);
>>  	drmmode_crtc_private_ptr crtc = config->crtc[0]->driver_private;
>>  	drmmode_ptr mode = crtc->drmmode;
>>  	int ret, i, old_fb_id;
>> +	int emitted = 0;
>> +	drmmode_flipdata_ptr flipdata;
>> +	drmmode_flipevtcarrier_ptr flipcarrier;
>>
>>  	old_fb_id = mode->fb_id;
>>  	ret = drmModeAddFB(mode->fd, scrn->virtualX, scrn->virtualY,
>> @@ -1265,24 +1284,64 @@ drmmode_page_flip(DrawablePtr draw,  
>> PixmapPtr back, void *priv)
>>  		return FALSE;
>>  	}
>>
>> +	flipdata = calloc(1, sizeof(drmmode_flipdata_rec));
>> +	if (!flipdata) {
>> +		xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>> +		"flip queue: data alloc failed.\n");
>> +		goto error_undo;
>> +	}
>> +
>> +	flipdata->event_data = priv;
>> +	flipdata->drmmode = mode;
>> +
>>  	for (i = 0; i < config->num_crtc; i++) {
>>  		crtc = config->crtc[i]->driver_private;
>>
>>  		if (!config->crtc[i]->enabled)
>>  			continue;
>>
>> +		flipdata->flip_count++;
>> +
>> +		flipcarrier = calloc(1, sizeof(drmmode_flipevtcarrier_rec));
>> +		if (!flipcarrier) {
>> +			xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>> +				   "flip queue: carrier alloc failed.\n");
>> +			if (emitted == 0)
>> +				free(flipdata);
>> +			goto error_undo;
>> +		}
>> +
>> +		/* Only the reference crtc will finally deliver its page flip
>> +		 * completion event. All other crtc's events will be discarded.
>> +		 */
>> +		flipcarrier->dispatch_me = ((1 << i) == ref_crtc_hw_id);
>> +		flipcarrier->flipdata = flipdata;
>> +
>>  		ret = drmModePageFlip(mode->fd, crtc->mode_crtc->crtc_id,
>> -				      mode->fb_id, 0, priv);
>> +				      mode->fb_id, DRM_MODE_PAGE_FLIP_EVENT,
>> +				      flipcarrier);
>>  		if (ret) {
>>  			xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>>  				   "flip queue failed: %s\n", strerror(errno));
>> -			return FALSE;
>> +
>> +			free(flipcarrier);
>> +			if (emitted == 0)
>> +				free(flipdata);
>> +			goto error_undo;
>>  		}
>> +
>> +		emitted++;
>>  	}
>>
>> -	drmModeRmFB(mode->fd, old_fb_id);
>> +	/* Will release old fb after all crtc's completed flip. */
>> +	flipdata->old_fb_id = old_fb_id;
>>
>>  	return TRUE;
>> +
>> +error_undo:
>> +	drmModeRmFB(mode->fd, mode->fb_id);
>> +	mode->fb_id = old_fb_id;
>> +	return FALSE;
>>  }
>>
>>  #ifdef HAVE_LIBUDEV
>> @@ -1348,6 +1407,40 @@ drmmode_uevent_fini(ScrnInfoPtr scrn)
>>  }
>>
>>  static void
>> +drmmode_flip_handler(int fd, unsigned int frame, unsigned int  
>> tv_sec,
>> +		     unsigned int tv_usec, void *event_data)
>> +{
>> +	drmmode_flipevtcarrier_ptr flipcarrier = event_data;
>> +	drmmode_flipdata_ptr flipdata = flipcarrier->flipdata;
>> +	drmmode_ptr drmmode = flipdata->drmmode;
>> +
>> +	/* Is this the event whose info shall be delivered to higher  
>> level? */
>> +	if (flipcarrier->dispatch_me) {
>> +		/* Yes: Cache msc, ust for later delivery. */
>> +		flipdata->fe_frame = frame;
>> +		flipdata->fe_tv_sec = tv_sec;
>> +		flipdata->fe_tv_usec = tv_usec;
>> +	}
>> +	free(flipcarrier);
>> +
>> +	/* Last crtc completed flip? */
>> +	flipdata->flip_count--;
>> +	if (flipdata->flip_count > 0)
>> +		return;
>> +
>> +	/* Release framebuffer */
>> +	drmModeRmFB(drmmode->fd, flipdata->old_fb_id);
>> +
>> +	if (flipdata->event_data == NULL)
>> +		return;
>> +
>> +	/* Deliver cached msc, ust from reference crtc to flip event  
>> handler */
>> +	nouveau_dri2_flip_event_handler(flipdata->fe_frame, flipdata- 
>> >fe_tv_sec,
>> +					flipdata->fe_tv_usec, flipdata->event_data);
>> +	free(flipdata);
>> +}
>> +
>> +static void
>>  drmmode_wakeup_handler(pointer data, int err, pointer p)
>>  {
>>  	ScrnInfoPtr scrn = data;
>> @@ -1377,6 +1470,10 @@ drmmode_screen_init(ScreenPtr pScreen)
>>  	/* Plug in a vblank event handler */
>>  	drmmode->event_context.version = DRM_EVENT_CONTEXT_VERSION;
>>  	drmmode->event_context.vblank_handler =  
>> nouveau_dri2_vblank_handler;
>> +
>> +	/* Plug in a pageflip completion event handler */
>> +	drmmode->event_context.page_flip_handler = drmmode_flip_handler;
>> +
>>  	AddGeneralSocket(drmmode->fd);
>>
>>  	/* Register a wakeup handler to get informed on DRM events */
>> diff --git a/src/nouveau_dri2.c b/src/nouveau_dri2.c
>> index 1a68ed3..87eaf08 100644
>> --- a/src/nouveau_dri2.c
>> +++ b/src/nouveau_dri2.c
>> @@ -136,6 +136,7 @@ struct nouveau_dri2_vblank_state {
>>  	DRI2BufferPtr src;
>>  	DRI2SwapEventPtr func;
>>  	void *data;
>> +	unsigned int frame;
>>  };
>>
>>  static Bool
>> @@ -222,6 +223,18 @@ nouveau_dri2_finish_swap(DrawablePtr draw,  
>> unsigned int frame,
>>  	REGION_INIT(0, &reg, (&(BoxRec){ 0, 0, draw->width, draw- 
>> >height }), 0);
>>  	REGION_TRANSLATE(0, &reg, draw->x, draw->y);
>>
>> +	/* Main crtc for this drawable shall finally deliver pageflip  
>> event. */
>> +	unsigned int ref_crtc_hw_id = nv_window_belongs_to_crtc(scrn,  
>> draw->x,
>> +								draw->y,
>> +								draw->width,
>> +								draw->height);
>> +
>> +	/* Whenever first crtc is involved, choose it as reference, as
>> +	 * its vblank event triggered this swap.
>> +	 */
>> +	if (ref_crtc_hw_id & 1)
>> +		ref_crtc_hw_id = 1;
>> +
>>  	/* Throttle on the previous frame before swapping */
>>  	nouveau_bo_map(dst_bo, NOUVEAU_BO_RD);
>>  	nouveau_bo_unmap(dst_bo);
>> @@ -246,7 +259,7 @@ nouveau_dri2_finish_swap(DrawablePtr draw,  
>> unsigned int frame,
>>
>>  		if (DRI2CanFlip(draw)) {
>>  			type = DRI2_FLIP_COMPLETE;
>> -			ret = drmmode_page_flip(draw, src_pix, s);
>> +			ret = drmmode_page_flip(draw, src_pix, s, ref_crtc_hw_id);
>>  			if (!ret)
>>  				goto out;
>>  		}
>> @@ -255,6 +268,10 @@ nouveau_dri2_finish_swap(DrawablePtr draw,  
>> unsigned int frame,
>>  		SWAP(nouveau_pixmap(dst_pix)->bo, nouveau_pixmap(src_pix)->bo);
>>
>>  		DamageRegionProcessPending(draw);
>> +
>> +		/* If it is a page flip, finish it in the flip event handler. */
>> +		if (type == DRI2_FLIP_COMPLETE)
>> +			return;
>>  	} else {
>>  		type = DRI2_BLIT_COMPLETE;
>>
>> @@ -289,7 +306,7 @@ nouveau_dri2_schedule_swap(ClientPtr client,  
>> DrawablePtr draw,
>>  			   DRI2SwapEventPtr func, void *data)
>>  {
>>  	struct nouveau_dri2_vblank_state *s;
>> -	CARD64 current_msc;
>> +	CARD64 current_msc, expect_msc;
>>  	int ret;
>>
>>  	/* Initialize a swap structure */
>> @@ -298,7 +315,7 @@ nouveau_dri2_schedule_swap(ClientPtr client,  
>> DrawablePtr draw,
>>  		return FALSE;
>>
>>  	*s = (struct nouveau_dri2_vblank_state)
>> -		{ SWAP, client, draw->id, dst, src, func, data };
>> +		{ SWAP, client, draw->id, dst, src, func, data, 0 };
>>
>>  	if (can_sync_to_vblank(draw)) {
>>  		/* Get current sequence */
>> @@ -316,10 +333,10 @@ nouveau_dri2_schedule_swap(ClientPtr client,  
>> DrawablePtr draw,
>>  		ret = nouveau_wait_vblank(draw, DRM_VBLANK_ABSOLUTE |
>>  					  DRM_VBLANK_EVENT,
>>  					  max(current_msc, *target_msc - 1),
>> -					  NULL, NULL, s);
>> +					  &expect_msc, NULL, s);
>>  		if (ret)
>>  			goto fail;
>> -
>> +		s->frame = (unsigned int) expect_msc & 0xffffffff;
>>  	} else {
>>  		/* We can't/don't want to sync to vblank, just swap. */
>>  		nouveau_dri2_finish_swap(draw, 0, 0, 0, s);
>> @@ -423,6 +440,68 @@ nouveau_dri2_vblank_handler(int fd, unsigned  
>> int frame,
>>  	}
>>  }
>>
>> +void
>> +nouveau_dri2_flip_event_handler(unsigned int frame, unsigned int  
>> tv_sec,
>> +				unsigned int tv_usec, void *event_data)
>> +{
>> +	struct nouveau_dri2_vblank_state *flip = event_data;
>> +	DrawablePtr draw;
>> +	ScreenPtr screen;
>> +	ScrnInfoPtr scrn;
>> +	int status;
>> +	PixmapPtr pixmap;
>> +
>> +	status = dixLookupDrawable(&draw, flip->draw, serverClient,
>> +				   M_ANY, DixWriteAccess);
>> +	if (status != Success) {
>> +		free(flip);
>> +		return;
>> +	}
>> +
>> +	screen = draw->pScreen;
>> +	scrn = xf86Screens[screen->myNum];
>> +
>> +	pixmap = screen->GetScreenPixmap(screen);
>> +	xf86DrvMsg(scrn->scrnIndex, X_INFO,
>> +		   "%s:%d fevent[%p] width %d pitch %d (/4 %d)\n",
>> +		   __func__, __LINE__, flip, pixmap->drawable.width,
>> +		   pixmap->devKind, pixmap->devKind/4);
>> +
>> +	/* We assume our flips arrive in order, so we don't check the  
>> frame */
>> +	switch (flip->action) {
>> +	case SWAP:
>> +		/* Check for too small vblank count of pageflip completion,
>> +		 * taking wraparound into account. This usually means some
>> +		 * defective kms pageflip completion, causing wrong (msc, ust)
>> +		 * return values and possible visual corruption.
>> +		 * Skip test for frame == 0, as this is a valid constant value
>> +		 * reported by all Linux kernels at least up to Linux 3.0.
>> +		 */
>> +		if ((frame != 0) &&
>> +		    (frame < flip->frame) && (flip->frame - frame < 5)) {
>> +			xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>> +				   "%s: Pageflip has impossible msc %d < target_msc %d\n",
>> +				   __func__, frame, flip->frame);
>> +			/* All-Zero values signal failure of (msc, ust)
>> +			 * timestamping to client.
>> +			 */
>> +			frame = tv_sec = tv_usec = 0;
>> +		}
>> +
>> +		DRI2SwapComplete(flip->client, draw, frame, tv_sec, tv_usec,
>> +				 DRI2_FLIP_COMPLETE, flip->func,
>> +				 flip->data);
>> +		break;
>> +	default:
>> +		xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>> +			   "%s: unknown vblank event received\n", __func__);
>> +		/* Unknown type */
>> +		break;
>> +	}
>> +
>> +	free(flip);
>> +}
>> +
>>  Bool
>>  nouveau_dri2_init(ScreenPtr pScreen)
>>  {
>> diff --git a/src/nv_proto.h b/src/nv_proto.h
>> index 2e4fce0..2bd2ac7 100644
>> --- a/src/nv_proto.h
>> +++ b/src/nv_proto.h
>> @@ -7,7 +7,8 @@ void drmmode_adjust_frame(ScrnInfoPtr pScrn, int  
>> x, int y, int flags);
>>  void drmmode_remove_fb(ScrnInfoPtr pScrn);
>>  Bool drmmode_cursor_init(ScreenPtr pScreen);
>>  void drmmode_fbcon_copy(ScreenPtr pScreen);
>> -Bool drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void  
>> *priv);
>> +Bool drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv,
>> +		       unsigned int ref_crtc_hw_id);
>>  void drmmode_screen_init(ScreenPtr pScreen);
>>  void drmmode_screen_fini(ScreenPtr pScreen);
>>
>> @@ -26,6 +27,8 @@ Bool nouveau_allocate_surface(ScrnInfoPtr scrn,  
>> int width, int height,
>>  void nouveau_dri2_vblank_handler(int fd, unsigned int frame,
>>  				 unsigned int tv_sec, unsigned int tv_usec,
>>  				 void *event_data);
>> +void nouveau_dri2_flip_event_handler(unsigned int frame, unsigned  
>> int tv_sec,
>> +				     unsigned int tv_usec, void *event_data);
>>  Bool nouveau_dri2_init(ScreenPtr pScreen);
>>  void nouveau_dri2_fini(ScreenPtr pScreen);

*********************************************************************
Mario Kleiner
Max Planck Institute for Biological Cybernetics
Spemannstr. 38
72076 Tuebingen
Germany

e-mail: mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org
office: +49 (0)7071/601-1623
fax:    +49 (0)7071/601-616
www:    http://www.kyb.tuebingen.mpg.de/~kleinerm
*********************************************************************
"For a successful technology, reality must take precedence
over public relations, for Nature cannot be fooled."
(Richard Feynman)

Re: [PATCH 1/3] dri2: Implement handling of pageflip completion events.

[Francisco Jerez]

[-- Attachment #1.1.1: Type: text/plain, Size: 21227 bytes --]

Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org> writes:

> On Sep 8, 2011, at 12:45 AM, Francisco Jerez wrote:
>
>> Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org> writes:
>>
>>> Requests pageflip completion events from the kernel.
>>> Implements pageflip completion handler to finalize
>>> and timestamp swaps.
>>>
>>> Completion handler includes a consistency check, and
>>> disambiguation if multiple crtc's are involved in a
>>> pageflip (e.g., clone mode, extendend desktop). Only
>>> the timestamp of the crtc whose vblank event initially
>>> triggered the swap is used, but handler waits for flip
>>> completion on all involved crtc's before completing the
>>> swap and releasing the old framebuffer.
>>>
>>> This code is almost identical to the code used in the
>>> ati/radeon ddx and intel ddx.
>>>
>> There's a good reason that I held myself back from doing this when I
>> wrote the rest of the SwapBuffers stuff; right now the X server
>> assumes
>> that the DDX can't handle more than one SwapBuffers request in
>> flight at
>> any given time, so, after a SwapBuffers request has been received, the
>> client is prevented from doing anything until the swap (and,
>> consequently, the whole rendering of the previous frame) has been
>> completed, that means that the client is forced to render each frame
>> in
>> lock-step, and it leads to a considerable performance loss.
>>
>> In my judgment it seemed quite dumb to wire up all the page-flipping
>> infrastructure together, only to notice that it was slowing things
>> down
>> even further (since performance was the main point I had for
>> it...). As
>> the ability to report accurate swap completion events seemed to be of
>> comparatively limited usefulness, I made the DDX pretend the buffers
>> are
>> swapped one frame before they actually are as a temporary workaround
>> (see the comment at the end of nouveau_dri2_finish_swap()).
>>
>
> Hi, thanks for the comments.

Thank you for looking into this :)
>
> I see your point, but at least as a starting point for the first
> iteration i don't think the current dri2 implementation of pageflips
> was a dumb decision.
>
> It is the same default "double buffer" behaviour that the binary
> drivers on Linux and also on other os'es (OS/X and Windows) expose.

Not the nvidia one, last time I checked.

> As a default i think it makes sense if an application wants tight
> control over presentation timing or - in the case of games - wants to
> prevent irritating lag between user input and visual updates -- limit
> the number of frames that the game can prerender.
>
> On the intel and ati gpu's, purely double-buffered pageflipping is
> already a win for conserving memory bandwidth and because you avoid
> blocking the single command fifo for multiple rendering clients, as
> you have to if you use vsync'ed copy-blits to avoid tearing. This may
> be less of a win on nvidia because they have multiple fifo's or some
> independent dma engines if i understand correctly?

Yeah, but right now the sync-to-vblank is pushed through the main X
server channel, which means it stalls all X rendering until the next
vblank - that could be fixed though, by extending the kernel interface
to make it end up in the right channel, but I haven't found the
motivation to do it so far because it hasn't proved to be a big problem
in practice.

>
> Anyway, it's better for performance if clients can queue up multiple
> rendered frames for other non-interactive use cases, e.g., benchmarks
> or graphics demos. Or if client apps can decide themselves about
> presentation timing. That was the point of support for the
> oml_sync_control and intel_swap_events extensions and all the
> timestamping.
>
> My specific use case for this patchset is a popular free software
> toolkit (http://www.psychtoolbox.org) used by neuro-scientists and
> brain scientists in general for audio & visual stimulus presentation,
> i/o etc. . Nouveau in its current state, at least on the cards i
> tested, would be already a very suitable solution for doing this on
> linux+nvidia.
>
> The only missing "must-have" feature for such applications are very
> reliable and accurate presentation timestamps. Having those puts
> nouveau ahead of the binary blob for such apps. The workloads are
> usually not as demanding as current games and an occassional skipped
> frame is tolerable, but frequently getting wrong/misleading
> timestamps of when a frame was presented would be a total show- 
> stopper. Currently i have to blacklist nouveau in my toolkit just for
> that reason.
>
>> So, IMHO, this change depends on the X server N-buffering changes
>> going
>> in - actually the DRI2SwapLimit() API that (IIRC) Pauli Nieminen
>> proposed some time ago was all we needed, but it hasn't been accepted
>> upstream for some reason.
>>
>
> I was involved in that discussion at the time, iirc. I think having
> the DRI2SwapLimit() API would make a lot of sense as a first step and
> that those patches just got dropped due to maintainer-overload, not
> really too much for technical reasons. To do multi-buffering
> correctly, as specified by the oml_sync_control spec, a bit more than
> Paul's API for setting the swap_limit would be needed, either on the
> ddx driver level or in the x-server itself, e.g., to make sure the
> ordering of glXSwapBuffersMscOML() swaps is correct, no more than one
> swap gets executed per video refresh and to satisfy the divisor/
> remainder constraints correctly if they are used by a client.

At least in nouveau's case, all of these problems are either already
solved or already present (even if you force it to do double-buffering),
and multi-buffering doesn't change the nature of the problem for us in
any way.

With the current implementation (and IIRC it's the same on both radeon
and intel) the divisor/remainder relation is ignored in the case where
the gpu is too busy to finish its rendering in time for the predicted
MSC; the flip is carried out as soon as the GPU finishes, possibly a few
vblank periods later.

To fix this properly in nouveau, I think it would be good to push the
divisor/remainder calculation down to the kernel (second reason so far
to extend the kernel interface), but once it's done we'll get the
divisor/remainder relation right no matter if multibuffering is being
used or not.

> Special cases which are not important for typical games or benchmarks
> but important for toolkits with precise timing needs. I actually
> wanted to work on that, but didn't get around to do it so far. First
> i'd like to have nouveau at the same level of timing functionality as
> ati and intel.
>
> Could we have an optional nouveau-ddx xorg.conf parameter to select
> between the current codepath and the "lower-performance but correct
> timestamping" path implemented in these patches? Something like
> "EnableTriplebuffering" or "Swaplimit" or
> "MaxNumberPrerenderedFrames"?

IMHO getting a small (and required) fix (the swaplimit API) into one
software component is more advisable from the maintainership standpoint
than putting in place two different codepaths in another software
component, both of which are broken in its own way.

> I think having such a setting would make sense anyway, even if Paul's
> API is implemented, exactly to control things like max number of
> prerendered frames for games and apps which only use glXSwapBuffers()
> but should have some control over input lag.
>
> The latest intel ddx seems to do the same with a "Triplebuffering"
> setting.
>
> The setting could default to your current performance
> implementation. The path in the new patches would get pretty frequent
> exercise &  testing by myself and currently a couple of hundred happy
> neuro- 
> scientists.
>
> thanks,
> -mario
>
>>> Signed-off-by: Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org>
>>> ---
>>>  src/drmmode_display.c |  105 +++++++++++++++++++++++++++++++++++++
>>> ++++++++++--
>>>  src/nouveau_dri2.c    |   89 +++++++++++++++++++++++++++++++++++++
>>> ++--
>>>  src/nv_proto.h        |    5 ++-
>>>  3 files changed, 189 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/src/drmmode_display.c b/src/drmmode_display.c
>>> index 3afef66..bcb2a94 100644
>>> --- a/src/drmmode_display.c
>>> +++ b/src/drmmode_display.c
>>> @@ -83,6 +83,21 @@ typedef struct {
>>>      drmmode_prop_ptr props;
>>>  } drmmode_output_private_rec, *drmmode_output_private_ptr;
>>>
>>> +typedef struct {
>>> +    drmmode_ptr drmmode;
>>> +    unsigned old_fb_id;
>>> +    int flip_count;
>>> +    void *event_data;
>>> +    unsigned int fe_frame;
>>> +    unsigned int fe_tv_sec;
>>> +    unsigned int fe_tv_usec;
>>> +} drmmode_flipdata_rec, *drmmode_flipdata_ptr;
>>> +
>>> +typedef struct {
>>> +    drmmode_flipdata_ptr flipdata;
>>> +    Bool dispatch_me;
>>> +} drmmode_flipevtcarrier_rec, *drmmode_flipevtcarrier_ptr;
>>> +
>>>  static void drmmode_output_dpms(xf86OutputPtr output, int mode);
>>>
>>>  static drmmode_ptr
>>> @@ -1246,13 +1261,17 @@ drmmode_cursor_init(ScreenPtr pScreen)
>>>  }
>>>
>>>  Bool
>>> -drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv)
>>> +drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv,
>>> +		  unsigned int ref_crtc_hw_id)
>>>  {
>>>  	ScrnInfoPtr scrn = xf86Screens[draw->pScreen->myNum];
>>>  	xf86CrtcConfigPtr config = XF86_CRTC_CONFIG_PTR(scrn);
>>>  	drmmode_crtc_private_ptr crtc = config->crtc[0]->driver_private;
>>>  	drmmode_ptr mode = crtc->drmmode;
>>>  	int ret, i, old_fb_id;
>>> +	int emitted = 0;
>>> +	drmmode_flipdata_ptr flipdata;
>>> +	drmmode_flipevtcarrier_ptr flipcarrier;
>>>
>>>  	old_fb_id = mode->fb_id;
>>>  	ret = drmModeAddFB(mode->fd, scrn->virtualX, scrn->virtualY,
>>> @@ -1265,24 +1284,64 @@ drmmode_page_flip(DrawablePtr draw,
>>> PixmapPtr back, void *priv)
>>>  		return FALSE;
>>>  	}
>>>
>>> +	flipdata = calloc(1, sizeof(drmmode_flipdata_rec));
>>> +	if (!flipdata) {
>>> +		xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>>> +		"flip queue: data alloc failed.\n");
>>> +		goto error_undo;
>>> +	}
>>> +
>>> +	flipdata->event_data = priv;
>>> +	flipdata->drmmode = mode;
>>> +
>>>  	for (i = 0; i < config->num_crtc; i++) {
>>>  		crtc = config->crtc[i]->driver_private;
>>>
>>>  		if (!config->crtc[i]->enabled)
>>>  			continue;
>>>
>>> +		flipdata->flip_count++;
>>> +
>>> +		flipcarrier = calloc(1, sizeof(drmmode_flipevtcarrier_rec));
>>> +		if (!flipcarrier) {
>>> +			xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>>> +				   "flip queue: carrier alloc failed.\n");
>>> +			if (emitted == 0)
>>> +				free(flipdata);
>>> +			goto error_undo;
>>> +		}
>>> +
>>> +		/* Only the reference crtc will finally deliver its page flip
>>> +		 * completion event. All other crtc's events will be discarded.
>>> +		 */
>>> +		flipcarrier->dispatch_me = ((1 << i) == ref_crtc_hw_id);
>>> +		flipcarrier->flipdata = flipdata;
>>> +
>>>  		ret = drmModePageFlip(mode->fd, crtc->mode_crtc->crtc_id,
>>> -				      mode->fb_id, 0, priv);
>>> +				      mode->fb_id, DRM_MODE_PAGE_FLIP_EVENT,
>>> +				      flipcarrier);
>>>  		if (ret) {
>>>  			xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>>>  				   "flip queue failed: %s\n", strerror(errno));
>>> -			return FALSE;
>>> +
>>> +			free(flipcarrier);
>>> +			if (emitted == 0)
>>> +				free(flipdata);
>>> +			goto error_undo;
>>>  		}
>>> +
>>> +		emitted++;
>>>  	}
>>>
>>> -	drmModeRmFB(mode->fd, old_fb_id);
>>> +	/* Will release old fb after all crtc's completed flip. */
>>> +	flipdata->old_fb_id = old_fb_id;
>>>
>>>  	return TRUE;
>>> +
>>> +error_undo:
>>> +	drmModeRmFB(mode->fd, mode->fb_id);
>>> +	mode->fb_id = old_fb_id;
>>> +	return FALSE;
>>>  }
>>>
>>>  #ifdef HAVE_LIBUDEV
>>> @@ -1348,6 +1407,40 @@ drmmode_uevent_fini(ScrnInfoPtr scrn)
>>>  }
>>>
>>>  static void
>>> +drmmode_flip_handler(int fd, unsigned int frame, unsigned int
>>> tv_sec,
>>> +		     unsigned int tv_usec, void *event_data)
>>> +{
>>> +	drmmode_flipevtcarrier_ptr flipcarrier = event_data;
>>> +	drmmode_flipdata_ptr flipdata = flipcarrier->flipdata;
>>> +	drmmode_ptr drmmode = flipdata->drmmode;
>>> +
>>> +	/* Is this the event whose info shall be delivered to higher
>>> level? */
>>> +	if (flipcarrier->dispatch_me) {
>>> +		/* Yes: Cache msc, ust for later delivery. */
>>> +		flipdata->fe_frame = frame;
>>> +		flipdata->fe_tv_sec = tv_sec;
>>> +		flipdata->fe_tv_usec = tv_usec;
>>> +	}
>>> +	free(flipcarrier);
>>> +
>>> +	/* Last crtc completed flip? */
>>> +	flipdata->flip_count--;
>>> +	if (flipdata->flip_count > 0)
>>> +		return;
>>> +
>>> +	/* Release framebuffer */
>>> +	drmModeRmFB(drmmode->fd, flipdata->old_fb_id);
>>> +
>>> +	if (flipdata->event_data == NULL)
>>> +		return;
>>> +
>>> +	/* Deliver cached msc, ust from reference crtc to flip event
>>> handler */
>>> +	nouveau_dri2_flip_event_handler(flipdata->fe_frame, flipdata-
>>> >fe_tv_sec,
>>> +					flipdata->fe_tv_usec, flipdata->event_data);
>>> +	free(flipdata);
>>> +}
>>> +
>>> +static void
>>>  drmmode_wakeup_handler(pointer data, int err, pointer p)
>>>  {
>>>  	ScrnInfoPtr scrn = data;
>>> @@ -1377,6 +1470,10 @@ drmmode_screen_init(ScreenPtr pScreen)
>>>  	/* Plug in a vblank event handler */
>>>  	drmmode->event_context.version = DRM_EVENT_CONTEXT_VERSION;
>>>  	drmmode->event_context.vblank_handler =
>>> nouveau_dri2_vblank_handler;
>>> +
>>> +	/* Plug in a pageflip completion event handler */
>>> +	drmmode->event_context.page_flip_handler = drmmode_flip_handler;
>>> +
>>>  	AddGeneralSocket(drmmode->fd);
>>>
>>>  	/* Register a wakeup handler to get informed on DRM events */
>>> diff --git a/src/nouveau_dri2.c b/src/nouveau_dri2.c
>>> index 1a68ed3..87eaf08 100644
>>> --- a/src/nouveau_dri2.c
>>> +++ b/src/nouveau_dri2.c
>>> @@ -136,6 +136,7 @@ struct nouveau_dri2_vblank_state {
>>>  	DRI2BufferPtr src;
>>>  	DRI2SwapEventPtr func;
>>>  	void *data;
>>> +	unsigned int frame;
>>>  };
>>>
>>>  static Bool
>>> @@ -222,6 +223,18 @@ nouveau_dri2_finish_swap(DrawablePtr draw,
>>> unsigned int frame,
>>>  	REGION_INIT(0, &reg, (&(BoxRec){ 0, 0, draw->width, draw-
>>> >height }), 0);
>>>  	REGION_TRANSLATE(0, &reg, draw->x, draw->y);
>>>
>>> +	/* Main crtc for this drawable shall finally deliver pageflip
>>> event. */
>>> +	unsigned int ref_crtc_hw_id = nv_window_belongs_to_crtc(scrn,
>>> draw->x,
>>> +								draw->y,
>>> +								draw->width,
>>> +								draw->height);
>>> +
>>> +	/* Whenever first crtc is involved, choose it as reference, as
>>> +	 * its vblank event triggered this swap.
>>> +	 */
>>> +	if (ref_crtc_hw_id & 1)
>>> +		ref_crtc_hw_id = 1;
>>> +
>>>  	/* Throttle on the previous frame before swapping */
>>>  	nouveau_bo_map(dst_bo, NOUVEAU_BO_RD);
>>>  	nouveau_bo_unmap(dst_bo);
>>> @@ -246,7 +259,7 @@ nouveau_dri2_finish_swap(DrawablePtr draw,
>>> unsigned int frame,
>>>
>>>  		if (DRI2CanFlip(draw)) {
>>>  			type = DRI2_FLIP_COMPLETE;
>>> -			ret = drmmode_page_flip(draw, src_pix, s);
>>> +			ret = drmmode_page_flip(draw, src_pix, s, ref_crtc_hw_id);
>>>  			if (!ret)
>>>  				goto out;
>>>  		}
>>> @@ -255,6 +268,10 @@ nouveau_dri2_finish_swap(DrawablePtr draw,
>>> unsigned int frame,
>>>  		SWAP(nouveau_pixmap(dst_pix)->bo, nouveau_pixmap(src_pix)->bo);
>>>
>>>  		DamageRegionProcessPending(draw);
>>> +
>>> +		/* If it is a page flip, finish it in the flip event handler. */
>>> +		if (type == DRI2_FLIP_COMPLETE)
>>> +			return;
>>>  	} else {
>>>  		type = DRI2_BLIT_COMPLETE;
>>>
>>> @@ -289,7 +306,7 @@ nouveau_dri2_schedule_swap(ClientPtr client,
>>> DrawablePtr draw,
>>>  			   DRI2SwapEventPtr func, void *data)
>>>  {
>>>  	struct nouveau_dri2_vblank_state *s;
>>> -	CARD64 current_msc;
>>> +	CARD64 current_msc, expect_msc;
>>>  	int ret;
>>>
>>>  	/* Initialize a swap structure */
>>> @@ -298,7 +315,7 @@ nouveau_dri2_schedule_swap(ClientPtr client,
>>> DrawablePtr draw,
>>>  		return FALSE;
>>>
>>>  	*s = (struct nouveau_dri2_vblank_state)
>>> -		{ SWAP, client, draw->id, dst, src, func, data };
>>> +		{ SWAP, client, draw->id, dst, src, func, data, 0 };
>>>
>>>  	if (can_sync_to_vblank(draw)) {
>>>  		/* Get current sequence */
>>> @@ -316,10 +333,10 @@ nouveau_dri2_schedule_swap(ClientPtr client,
>>> DrawablePtr draw,
>>>  		ret = nouveau_wait_vblank(draw, DRM_VBLANK_ABSOLUTE |
>>>  					  DRM_VBLANK_EVENT,
>>>  					  max(current_msc, *target_msc - 1),
>>> -					  NULL, NULL, s);
>>> +					  &expect_msc, NULL, s);
>>>  		if (ret)
>>>  			goto fail;
>>> -
>>> +		s->frame = (unsigned int) expect_msc & 0xffffffff;
>>>  	} else {
>>>  		/* We can't/don't want to sync to vblank, just swap. */
>>>  		nouveau_dri2_finish_swap(draw, 0, 0, 0, s);
>>> @@ -423,6 +440,68 @@ nouveau_dri2_vblank_handler(int fd, unsigned
>>> int frame,
>>>  	}
>>>  }
>>>
>>> +void
>>> +nouveau_dri2_flip_event_handler(unsigned int frame, unsigned int
>>> tv_sec,
>>> +				unsigned int tv_usec, void *event_data)
>>> +{
>>> +	struct nouveau_dri2_vblank_state *flip = event_data;
>>> +	DrawablePtr draw;
>>> +	ScreenPtr screen;
>>> +	ScrnInfoPtr scrn;
>>> +	int status;
>>> +	PixmapPtr pixmap;
>>> +
>>> +	status = dixLookupDrawable(&draw, flip->draw, serverClient,
>>> +				   M_ANY, DixWriteAccess);
>>> +	if (status != Success) {
>>> +		free(flip);
>>> +		return;
>>> +	}
>>> +
>>> +	screen = draw->pScreen;
>>> +	scrn = xf86Screens[screen->myNum];
>>> +
>>> +	pixmap = screen->GetScreenPixmap(screen);
>>> +	xf86DrvMsg(scrn->scrnIndex, X_INFO,
>>> +		   "%s:%d fevent[%p] width %d pitch %d (/4 %d)\n",
>>> +		   __func__, __LINE__, flip, pixmap->drawable.width,
>>> +		   pixmap->devKind, pixmap->devKind/4);
>>> +
>>> +	/* We assume our flips arrive in order, so we don't check the
>>> frame */
>>> +	switch (flip->action) {
>>> +	case SWAP:
>>> +		/* Check for too small vblank count of pageflip completion,
>>> +		 * taking wraparound into account. This usually means some
>>> +		 * defective kms pageflip completion, causing wrong (msc, ust)
>>> +		 * return values and possible visual corruption.
>>> +		 * Skip test for frame == 0, as this is a valid constant value
>>> +		 * reported by all Linux kernels at least up to Linux 3.0.
>>> +		 */
>>> +		if ((frame != 0) &&
>>> +		    (frame < flip->frame) && (flip->frame - frame < 5)) {
>>> +			xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>>> +				   "%s: Pageflip has impossible msc %d < target_msc %d\n",
>>> +				   __func__, frame, flip->frame);
>>> +			/* All-Zero values signal failure of (msc, ust)
>>> +			 * timestamping to client.
>>> +			 */
>>> +			frame = tv_sec = tv_usec = 0;
>>> +		}
>>> +
>>> +		DRI2SwapComplete(flip->client, draw, frame, tv_sec, tv_usec,
>>> +				 DRI2_FLIP_COMPLETE, flip->func,
>>> +				 flip->data);
>>> +		break;
>>> +	default:
>>> +		xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>>> +			   "%s: unknown vblank event received\n", __func__);
>>> +		/* Unknown type */
>>> +		break;
>>> +	}
>>> +
>>> +	free(flip);
>>> +}
>>> +
>>>  Bool
>>>  nouveau_dri2_init(ScreenPtr pScreen)
>>>  {
>>> diff --git a/src/nv_proto.h b/src/nv_proto.h
>>> index 2e4fce0..2bd2ac7 100644
>>> --- a/src/nv_proto.h
>>> +++ b/src/nv_proto.h
>>> @@ -7,7 +7,8 @@ void drmmode_adjust_frame(ScrnInfoPtr pScrn, int x,
>>> int y, int flags);
>>>  void drmmode_remove_fb(ScrnInfoPtr pScrn);
>>>  Bool drmmode_cursor_init(ScreenPtr pScreen);
>>>  void drmmode_fbcon_copy(ScreenPtr pScreen);
>>> -Bool drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void
>>> *priv);
>>> +Bool drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv,
>>> +		       unsigned int ref_crtc_hw_id);
>>>  void drmmode_screen_init(ScreenPtr pScreen);
>>>  void drmmode_screen_fini(ScreenPtr pScreen);
>>>
>>> @@ -26,6 +27,8 @@ Bool nouveau_allocate_surface(ScrnInfoPtr scrn,
>>> int width, int height,
>>>  void nouveau_dri2_vblank_handler(int fd, unsigned int frame,
>>>  				 unsigned int tv_sec, unsigned int tv_usec,
>>>  				 void *event_data);
>>> +void nouveau_dri2_flip_event_handler(unsigned int frame, unsigned
>>> int tv_sec,
>>> +				     unsigned int tv_usec, void *event_data);
>>>  Bool nouveau_dri2_init(ScreenPtr pScreen);
>>>  void nouveau_dri2_fini(ScreenPtr pScreen);
>
> *********************************************************************
> Mario Kleiner
> Max Planck Institute for Biological Cybernetics
> Spemannstr. 38
> 72076 Tuebingen
> Germany
>
> e-mail: mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org
> office: +49 (0)7071/601-1623
> fax:    +49 (0)7071/601-616
> www:    http://www.kyb.tuebingen.mpg.de/~kleinerm
> *********************************************************************
> "For a successful technology, reality must take precedence
> over public relations, for Nature cannot be fooled."
> (Richard Feynman)

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Re: [PATCH 1/3] dri2: Implement handling of pageflip completion events.

[Mario Kleiner]

On 09/09/2011 11:05 PM, Francisco Jerez wrote:
> Mario Kleiner<mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org>  writes:
>
>> On Sep 8, 2011, at 12:45 AM, Francisco Jerez wrote:
>>
>>> Mario Kleiner<mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org>  writes:
>>>
>>>> Requests pageflip completion events from the kernel.
>>>> Implements pageflip completion handler to finalize
>>>> and timestamp swaps.
>>>>
>>>> Completion handler includes a consistency check, and
>>>> disambiguation if multiple crtc's are involved in a
>>>> pageflip (e.g., clone mode, extendend desktop). Only
>>>> the timestamp of the crtc whose vblank event initially
>>>> triggered the swap is used, but handler waits for flip
>>>> completion on all involved crtc's before completing the
>>>> swap and releasing the old framebuffer.
>>>>
>>>> This code is almost identical to the code used in the
>>>> ati/radeon ddx and intel ddx.
>>>>
>>> There's a good reason that I held myself back from doing this when I
>>> wrote the rest of the SwapBuffers stuff; right now the X server
>>> assumes
>>> that the DDX can't handle more than one SwapBuffers request in
>>> flight at
>>> any given time, so, after a SwapBuffers request has been received, the
>>> client is prevented from doing anything until the swap (and,
>>> consequently, the whole rendering of the previous frame) has been
>>> completed, that means that the client is forced to render each frame
>>> in
>>> lock-step, and it leads to a considerable performance loss.
>>>
>>> In my judgment it seemed quite dumb to wire up all the page-flipping
>>> infrastructure together, only to notice that it was slowing things
>>> down
>>> even further (since performance was the main point I had for
>>> it...). As
>>> the ability to report accurate swap completion events seemed to be of
>>> comparatively limited usefulness, I made the DDX pretend the buffers
>>> are
>>> swapped one frame before they actually are as a temporary workaround
>>> (see the comment at the end of nouveau_dri2_finish_swap()).
>>>
>>
>> Hi, thanks for the comments.
>
> Thank you for looking into this :)
>>

Sorry for the late reply. I'm a bit slow at the moment.

>> I see your point, but at least as a starting point for the first
>> iteration i don't think the current dri2 implementation of pageflips
>> was a dumb decision.
>>
>> It is the same default "double buffer" behaviour that the binary
>> drivers on Linux and also on other os'es (OS/X and Windows) expose.
>
> Not the nvidia one, last time I checked.
>

It doesn't neccessarily block glXXX drawing command submission, but it 
doesn't do triple-buffering by default. It blocks rendering until swap 
completion, probably just queueing up drawing commands internally.

Here is how my toolkit waits for swap completion with the binary blob on 
linux, os/x and windows:

1. glXSwapBuffers() (aka SwapBuffers() on Windows aka 
CGLFlushDrawable()) on OS/X).

2. glBegin(GL_POINTS); glVertex2i(10,10); glEnd();
3. glFinish();
4. Read clock, scanout position etc. compute swap completion timestamp.

On any tested binary NVidia, ATI or Intel drivers on any tested Windows, 
OS/X or Linux version this blocks in glFinish() until swap completion, 
at least for page-flipped fullscreen swaps if the optional "triple 
buffering" option is not selected in the driver control panel. This 
method is successfully tested on multiple ten thousand users setups over 
at least the last six years.

So glFinish() waits for draw completion and drawing apparently waits for 
swap completion - strictly double-buffered with the drivers default 
settings. Or at least the observable behaviour of the drivers is 
consistent with this assumption.

>> As a default i think it makes sense if an application wants tight
>> control over presentation timing or - in the case of games - wants to
>> prevent irritating lag between user input and visual updates -- limit
>> the number of frames that the game can prerender.
>>
>> On the intel and ati gpu's, purely double-buffered pageflipping is
>> already a win for conserving memory bandwidth and because you avoid
>> blocking the single command fifo for multiple rendering clients, as
>> you have to if you use vsync'ed copy-blits to avoid tearing. This may
>> be less of a win on nvidia because they have multiple fifo's or some
>> independent dma engines if i understand correctly?
>
> Yeah, but right now the sync-to-vblank is pushed through the main X
> server channel, which means it stalls all X rendering until the next
> vblank - that could be fixed though, by extending the kernel interface
> to make it end up in the right channel, but I haven't found the
> motivation to do it so far because it hasn't proved to be a big problem
> in practice.
>
>>
>> Anyway, it's better for performance if clients can queue up multiple
>> rendered frames for other non-interactive use cases, e.g., benchmarks
>> or graphics demos. Or if client apps can decide themselves about
>> presentation timing. That was the point of support for the
>> oml_sync_control and intel_swap_events extensions and all the
>> timestamping.
>>
>> My specific use case for this patchset is a popular free software
>> toolkit (http://www.psychtoolbox.org) used by neuro-scientists and
>> brain scientists in general for audio&  visual stimulus presentation,
>> i/o etc. . Nouveau in its current state, at least on the cards i
>> tested, would be already a very suitable solution for doing this on
>> linux+nvidia.
>>
>> The only missing "must-have" feature for such applications are very
>> reliable and accurate presentation timestamps. Having those puts
>> nouveau ahead of the binary blob for such apps. The workloads are
>> usually not as demanding as current games and an occassional skipped
>> frame is tolerable, but frequently getting wrong/misleading
>> timestamps of when a frame was presented would be a total show-
>> stopper. Currently i have to blacklist nouveau in my toolkit just for
>> that reason.
>>
>>> So, IMHO, this change depends on the X server N-buffering changes
>>> going
>>> in - actually the DRI2SwapLimit() API that (IIRC) Pauli Nieminen
>>> proposed some time ago was all we needed, but it hasn't been accepted
>>> upstream for some reason.
>>>
>>
>> I was involved in that discussion at the time, iirc. I think having
>> the DRI2SwapLimit() API would make a lot of sense as a first step and
>> that those patches just got dropped due to maintainer-overload, not
>> really too much for technical reasons. To do multi-buffering
>> correctly, as specified by the oml_sync_control spec, a bit more than
>> Paul's API for setting the swap_limit would be needed, either on the
>> ddx driver level or in the x-server itself, e.g., to make sure the
>> ordering of glXSwapBuffersMscOML() swaps is correct, no more than one
>> swap gets executed per video refresh and to satisfy the divisor/
>> remainder constraints correctly if they are used by a client.
>
> At least in nouveau's case, all of these problems are either already
> solved or already present (even if you force it to do double-buffering),
> and multi-buffering doesn't change the nature of the problem for us in
> any way.
>

Ok. Thanks for explaining.

> With the current implementation (and IIRC it's the same on both radeon
> and intel) the divisor/remainder relation is ignored in the case where
> the gpu is too busy to finish its rendering in time for the predicted
> MSC; the flip is carried out as soon as the GPU finishes, possibly a few
> vblank periods later.
>
> To fix this properly in nouveau, I think it would be good to push the
> divisor/remainder calculation down to the kernel (second reason so far
> to extend the kernel interface), but once it's done we'll get the
> divisor/remainder relation right no matter if multibuffering is being
> used or not.
>

Agreed on that. The current fix only fixes the easy case where the 
client submits a swap request too late to satisfy the divisor/remainder 
relation, or where the relation is easily satisfiable. E.g., my toolkit 
uses it to make sure that a swap happens after a user specified 
deadline, but only on, e.g., odd numbered video refresh cycles, for the 
purpose of getting frame-sequential stereo right.

None of the current ddx handles the case where the backbuffer is still 
busy at the target vblank.

Imho there are a couple of things a pageflip ioctl() v2 should provide:

* Some support for frame-sequential stereo.
* 64 bit target_msc.
* Divisor/remainder in kernel.


>> Special cases which are not important for typical games or benchmarks
>> but important for toolkits with precise timing needs. I actually
>> wanted to work on that, but didn't get around to do it so far. First
>> i'd like to have nouveau at the same level of timing functionality as
>> ati and intel.
>>
>> Could we have an optional nouveau-ddx xorg.conf parameter to select
>> between the current codepath and the "lower-performance but correct
>> timestamping" path implemented in these patches? Something like
>> "EnableTriplebuffering" or "Swaplimit" or
>> "MaxNumberPrerenderedFrames"?
>
> IMHO getting a small (and required) fix (the swaplimit API) into one
> software component is more advisable from the maintainership standpoint
> than putting in place two different codepaths in another software
> component, both of which are broken in its own way.
>

I totally agree with you. But assume we finally manage to persuade Keith 
to integrate that API into 1.12, it would still be nice - at least for 
my users - if the nouveau ddx could optionally support a double-buffered 
mode with correct timestamps on current servers, e.g., 1.9 - 1.11.

I think the proposed patch should work for n-buffering on future servers 
with a swaplimit api, and for double-buffering with correct timestamping 
on current servers. For triple buffering on current servers it would be 
simple to add your current implementation back as a special case with 
only a few lines of code: Just don't request pageflip completion events 
from the kernel, so the whole pageflip callback gets skipped, and call 
DRI2SwapComplete() directly, as in the current ddx.

I think a x-org.conf option for selecting double-buffering / 
triple-buffering / n-buffering will be needed anyway, even with a 
swaplimit api in place, so we could add it now and use it to switch 
between double-buffering and n-buffering.

I'm not really sure what Keith remaining objections to Paul's imho 
rather small, simple and well reviewed swaplimit api patch are, or if we 
just have some kind of miscommunication about what specific patch we 
were talking about. I will try to look at it again next week.

thanks,
-mario


>> I think having such a setting would make sense anyway, even if Paul's
>> API is implemented, exactly to control things like max number of
>> prerendered frames for games and apps which only use glXSwapBuffers()
>> but should have some control over input lag.
>>
>> The latest intel ddx seems to do the same with a "Triplebuffering"
>> setting.
>>
>> The setting could default to your current performance
>> implementation. The path in the new patches would get pretty frequent
>> exercise&   testing by myself and currently a couple of hundred happy
>> neuro-
>> scientists.
>>
>> thanks,
>> -mario
>>
>>>> Signed-off-by: Mario Kleiner<mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org>
>>>> ---
>>>>   src/drmmode_display.c |  105 +++++++++++++++++++++++++++++++++++++
>>>> ++++++++++--
>>>>   src/nouveau_dri2.c    |   89 +++++++++++++++++++++++++++++++++++++
>>>> ++--
>>>>   src/nv_proto.h        |    5 ++-
>>>>   3 files changed, 189 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/src/drmmode_display.c b/src/drmmode_display.c
>>>> index 3afef66..bcb2a94 100644
>>>> --- a/src/drmmode_display.c
>>>> +++ b/src/drmmode_display.c
>>>> @@ -83,6 +83,21 @@ typedef struct {
>>>>       drmmode_prop_ptr props;
>>>>   } drmmode_output_private_rec, *drmmode_output_private_ptr;
>>>>
>>>> +typedef struct {
>>>> +    drmmode_ptr drmmode;
>>>> +    unsigned old_fb_id;
>>>> +    int flip_count;
>>>> +    void *event_data;
>>>> +    unsigned int fe_frame;
>>>> +    unsigned int fe_tv_sec;
>>>> +    unsigned int fe_tv_usec;
>>>> +} drmmode_flipdata_rec, *drmmode_flipdata_ptr;
>>>> +
>>>> +typedef struct {
>>>> +    drmmode_flipdata_ptr flipdata;
>>>> +    Bool dispatch_me;
>>>> +} drmmode_flipevtcarrier_rec, *drmmode_flipevtcarrier_ptr;
>>>> +
>>>>   static void drmmode_output_dpms(xf86OutputPtr output, int mode);
>>>>
>>>>   static drmmode_ptr
>>>> @@ -1246,13 +1261,17 @@ drmmode_cursor_init(ScreenPtr pScreen)
>>>>   }
>>>>
>>>>   Bool
>>>> -drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv)
>>>> +drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv,
>>>> +		  unsigned int ref_crtc_hw_id)
>>>>   {
>>>>   	ScrnInfoPtr scrn = xf86Screens[draw->pScreen->myNum];
>>>>   	xf86CrtcConfigPtr config = XF86_CRTC_CONFIG_PTR(scrn);
>>>>   	drmmode_crtc_private_ptr crtc = config->crtc[0]->driver_private;
>>>>   	drmmode_ptr mode = crtc->drmmode;
>>>>   	int ret, i, old_fb_id;
>>>> +	int emitted = 0;
>>>> +	drmmode_flipdata_ptr flipdata;
>>>> +	drmmode_flipevtcarrier_ptr flipcarrier;
>>>>
>>>>   	old_fb_id = mode->fb_id;
>>>>   	ret = drmModeAddFB(mode->fd, scrn->virtualX, scrn->virtualY,
>>>> @@ -1265,24 +1284,64 @@ drmmode_page_flip(DrawablePtr draw,
>>>> PixmapPtr back, void *priv)
>>>>   		return FALSE;
>>>>   	}
>>>>
>>>> +	flipdata = calloc(1, sizeof(drmmode_flipdata_rec));
>>>> +	if (!flipdata) {
>>>> +		xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>>>> +		"flip queue: data alloc failed.\n");
>>>> +		goto error_undo;
>>>> +	}
>>>> +
>>>> +	flipdata->event_data = priv;
>>>> +	flipdata->drmmode = mode;
>>>> +
>>>>   	for (i = 0; i<  config->num_crtc; i++) {
>>>>   		crtc = config->crtc[i]->driver_private;
>>>>
>>>>   		if (!config->crtc[i]->enabled)
>>>>   			continue;
>>>>
>>>> +		flipdata->flip_count++;
>>>> +
>>>> +		flipcarrier = calloc(1, sizeof(drmmode_flipevtcarrier_rec));
>>>> +		if (!flipcarrier) {
>>>> +			xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>>>> +				   "flip queue: carrier alloc failed.\n");
>>>> +			if (emitted == 0)
>>>> +				free(flipdata);
>>>> +			goto error_undo;
>>>> +		}
>>>> +
>>>> +		/* Only the reference crtc will finally deliver its page flip
>>>> +		 * completion event. All other crtc's events will be discarded.
>>>> +		 */
>>>> +		flipcarrier->dispatch_me = ((1<<  i) == ref_crtc_hw_id);
>>>> +		flipcarrier->flipdata = flipdata;
>>>> +
>>>>   		ret = drmModePageFlip(mode->fd, crtc->mode_crtc->crtc_id,
>>>> -				      mode->fb_id, 0, priv);
>>>> +				      mode->fb_id, DRM_MODE_PAGE_FLIP_EVENT,
>>>> +				      flipcarrier);
>>>>   		if (ret) {
>>>>   			xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>>>>   				   "flip queue failed: %s\n", strerror(errno));
>>>> -			return FALSE;
>>>> +
>>>> +			free(flipcarrier);
>>>> +			if (emitted == 0)
>>>> +				free(flipdata);
>>>> +			goto error_undo;
>>>>   		}
>>>> +
>>>> +		emitted++;
>>>>   	}
>>>>
>>>> -	drmModeRmFB(mode->fd, old_fb_id);
>>>> +	/* Will release old fb after all crtc's completed flip. */
>>>> +	flipdata->old_fb_id = old_fb_id;
>>>>
>>>>   	return TRUE;
>>>> +
>>>> +error_undo:
>>>> +	drmModeRmFB(mode->fd, mode->fb_id);
>>>> +	mode->fb_id = old_fb_id;
>>>> +	return FALSE;
>>>>   }
>>>>
>>>>   #ifdef HAVE_LIBUDEV
>>>> @@ -1348,6 +1407,40 @@ drmmode_uevent_fini(ScrnInfoPtr scrn)
>>>>   }
>>>>
>>>>   static void
>>>> +drmmode_flip_handler(int fd, unsigned int frame, unsigned int
>>>> tv_sec,
>>>> +		     unsigned int tv_usec, void *event_data)
>>>> +{
>>>> +	drmmode_flipevtcarrier_ptr flipcarrier = event_data;
>>>> +	drmmode_flipdata_ptr flipdata = flipcarrier->flipdata;
>>>> +	drmmode_ptr drmmode = flipdata->drmmode;
>>>> +
>>>> +	/* Is this the event whose info shall be delivered to higher
>>>> level? */
>>>> +	if (flipcarrier->dispatch_me) {
>>>> +		/* Yes: Cache msc, ust for later delivery. */
>>>> +		flipdata->fe_frame = frame;
>>>> +		flipdata->fe_tv_sec = tv_sec;
>>>> +		flipdata->fe_tv_usec = tv_usec;
>>>> +	}
>>>> +	free(flipcarrier);
>>>> +
>>>> +	/* Last crtc completed flip? */
>>>> +	flipdata->flip_count--;
>>>> +	if (flipdata->flip_count>  0)
>>>> +		return;
>>>> +
>>>> +	/* Release framebuffer */
>>>> +	drmModeRmFB(drmmode->fd, flipdata->old_fb_id);
>>>> +
>>>> +	if (flipdata->event_data == NULL)
>>>> +		return;
>>>> +
>>>> +	/* Deliver cached msc, ust from reference crtc to flip event
>>>> handler */
>>>> +	nouveau_dri2_flip_event_handler(flipdata->fe_frame, flipdata-
>>>>> fe_tv_sec,
>>>> +					flipdata->fe_tv_usec, flipdata->event_data);
>>>> +	free(flipdata);
>>>> +}
>>>> +
>>>> +static void
>>>>   drmmode_wakeup_handler(pointer data, int err, pointer p)
>>>>   {
>>>>   	ScrnInfoPtr scrn = data;
>>>> @@ -1377,6 +1470,10 @@ drmmode_screen_init(ScreenPtr pScreen)
>>>>   	/* Plug in a vblank event handler */
>>>>   	drmmode->event_context.version = DRM_EVENT_CONTEXT_VERSION;
>>>>   	drmmode->event_context.vblank_handler =
>>>> nouveau_dri2_vblank_handler;
>>>> +
>>>> +	/* Plug in a pageflip completion event handler */
>>>> +	drmmode->event_context.page_flip_handler = drmmode_flip_handler;
>>>> +
>>>>   	AddGeneralSocket(drmmode->fd);
>>>>
>>>>   	/* Register a wakeup handler to get informed on DRM events */
>>>> diff --git a/src/nouveau_dri2.c b/src/nouveau_dri2.c
>>>> index 1a68ed3..87eaf08 100644
>>>> --- a/src/nouveau_dri2.c
>>>> +++ b/src/nouveau_dri2.c
>>>> @@ -136,6 +136,7 @@ struct nouveau_dri2_vblank_state {
>>>>   	DRI2BufferPtr src;
>>>>   	DRI2SwapEventPtr func;
>>>>   	void *data;
>>>> +	unsigned int frame;
>>>>   };
>>>>
>>>>   static Bool
>>>> @@ -222,6 +223,18 @@ nouveau_dri2_finish_swap(DrawablePtr draw,
>>>> unsigned int frame,
>>>>   	REGION_INIT(0,&reg, (&(BoxRec){ 0, 0, draw->width, draw-
>>>>> height }), 0);
>>>>   	REGION_TRANSLATE(0,&reg, draw->x, draw->y);
>>>>
>>>> +	/* Main crtc for this drawable shall finally deliver pageflip
>>>> event. */
>>>> +	unsigned int ref_crtc_hw_id = nv_window_belongs_to_crtc(scrn,
>>>> draw->x,
>>>> +								draw->y,
>>>> +								draw->width,
>>>> +								draw->height);
>>>> +
>>>> +	/* Whenever first crtc is involved, choose it as reference, as
>>>> +	 * its vblank event triggered this swap.
>>>> +	 */
>>>> +	if (ref_crtc_hw_id&  1)
>>>> +		ref_crtc_hw_id = 1;
>>>> +
>>>>   	/* Throttle on the previous frame before swapping */
>>>>   	nouveau_bo_map(dst_bo, NOUVEAU_BO_RD);
>>>>   	nouveau_bo_unmap(dst_bo);
>>>> @@ -246,7 +259,7 @@ nouveau_dri2_finish_swap(DrawablePtr draw,
>>>> unsigned int frame,
>>>>
>>>>   		if (DRI2CanFlip(draw)) {
>>>>   			type = DRI2_FLIP_COMPLETE;
>>>> -			ret = drmmode_page_flip(draw, src_pix, s);
>>>> +			ret = drmmode_page_flip(draw, src_pix, s, ref_crtc_hw_id);
>>>>   			if (!ret)
>>>>   				goto out;
>>>>   		}
>>>> @@ -255,6 +268,10 @@ nouveau_dri2_finish_swap(DrawablePtr draw,
>>>> unsigned int frame,
>>>>   		SWAP(nouveau_pixmap(dst_pix)->bo, nouveau_pixmap(src_pix)->bo);
>>>>
>>>>   		DamageRegionProcessPending(draw);
>>>> +
>>>> +		/* If it is a page flip, finish it in the flip event handler. */
>>>> +		if (type == DRI2_FLIP_COMPLETE)
>>>> +			return;
>>>>   	} else {
>>>>   		type = DRI2_BLIT_COMPLETE;
>>>>
>>>> @@ -289,7 +306,7 @@ nouveau_dri2_schedule_swap(ClientPtr client,
>>>> DrawablePtr draw,
>>>>   			   DRI2SwapEventPtr func, void *data)
>>>>   {
>>>>   	struct nouveau_dri2_vblank_state *s;
>>>> -	CARD64 current_msc;
>>>> +	CARD64 current_msc, expect_msc;
>>>>   	int ret;
>>>>
>>>>   	/* Initialize a swap structure */
>>>> @@ -298,7 +315,7 @@ nouveau_dri2_schedule_swap(ClientPtr client,
>>>> DrawablePtr draw,
>>>>   		return FALSE;
>>>>
>>>>   	*s = (struct nouveau_dri2_vblank_state)
>>>> -		{ SWAP, client, draw->id, dst, src, func, data };
>>>> +		{ SWAP, client, draw->id, dst, src, func, data, 0 };
>>>>
>>>>   	if (can_sync_to_vblank(draw)) {
>>>>   		/* Get current sequence */
>>>> @@ -316,10 +333,10 @@ nouveau_dri2_schedule_swap(ClientPtr client,
>>>> DrawablePtr draw,
>>>>   		ret = nouveau_wait_vblank(draw, DRM_VBLANK_ABSOLUTE |
>>>>   					  DRM_VBLANK_EVENT,
>>>>   					  max(current_msc, *target_msc - 1),
>>>> -					  NULL, NULL, s);
>>>> +					&expect_msc, NULL, s);
>>>>   		if (ret)
>>>>   			goto fail;
>>>> -
>>>> +		s->frame = (unsigned int) expect_msc&  0xffffffff;
>>>>   	} else {
>>>>   		/* We can't/don't want to sync to vblank, just swap. */
>>>>   		nouveau_dri2_finish_swap(draw, 0, 0, 0, s);
>>>> @@ -423,6 +440,68 @@ nouveau_dri2_vblank_handler(int fd, unsigned
>>>> int frame,
>>>>   	}
>>>>   }
>>>>
>>>> +void
>>>> +nouveau_dri2_flip_event_handler(unsigned int frame, unsigned int
>>>> tv_sec,
>>>> +				unsigned int tv_usec, void *event_data)
>>>> +{
>>>> +	struct nouveau_dri2_vblank_state *flip = event_data;
>>>> +	DrawablePtr draw;
>>>> +	ScreenPtr screen;
>>>> +	ScrnInfoPtr scrn;
>>>> +	int status;
>>>> +	PixmapPtr pixmap;
>>>> +
>>>> +	status = dixLookupDrawable(&draw, flip->draw, serverClient,
>>>> +				   M_ANY, DixWriteAccess);
>>>> +	if (status != Success) {
>>>> +		free(flip);
>>>> +		return;
>>>> +	}
>>>> +
>>>> +	screen = draw->pScreen;
>>>> +	scrn = xf86Screens[screen->myNum];
>>>> +
>>>> +	pixmap = screen->GetScreenPixmap(screen);
>>>> +	xf86DrvMsg(scrn->scrnIndex, X_INFO,
>>>> +		   "%s:%d fevent[%p] width %d pitch %d (/4 %d)\n",
>>>> +		   __func__, __LINE__, flip, pixmap->drawable.width,
>>>> +		   pixmap->devKind, pixmap->devKind/4);
>>>> +
>>>> +	/* We assume our flips arrive in order, so we don't check the
>>>> frame */
>>>> +	switch (flip->action) {
>>>> +	case SWAP:
>>>> +		/* Check for too small vblank count of pageflip completion,
>>>> +		 * taking wraparound into account. This usually means some
>>>> +		 * defective kms pageflip completion, causing wrong (msc, ust)
>>>> +		 * return values and possible visual corruption.
>>>> +		 * Skip test for frame == 0, as this is a valid constant value
>>>> +		 * reported by all Linux kernels at least up to Linux 3.0.
>>>> +		 */
>>>> +		if ((frame != 0)&&
>>>> +		    (frame<  flip->frame)&&  (flip->frame - frame<  5)) {
>>>> +			xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>>>> +				   "%s: Pageflip has impossible msc %d<  target_msc %d\n",
>>>> +				   __func__, frame, flip->frame);
>>>> +			/* All-Zero values signal failure of (msc, ust)
>>>> +			 * timestamping to client.
>>>> +			 */
>>>> +			frame = tv_sec = tv_usec = 0;
>>>> +		}
>>>> +
>>>> +		DRI2SwapComplete(flip->client, draw, frame, tv_sec, tv_usec,
>>>> +				 DRI2_FLIP_COMPLETE, flip->func,
>>>> +				 flip->data);
>>>> +		break;
>>>> +	default:
>>>> +		xf86DrvMsg(scrn->scrnIndex, X_WARNING,
>>>> +			   "%s: unknown vblank event received\n", __func__);
>>>> +		/* Unknown type */
>>>> +		break;
>>>> +	}
>>>> +
>>>> +	free(flip);
>>>> +}
>>>> +
>>>>   Bool
>>>>   nouveau_dri2_init(ScreenPtr pScreen)
>>>>   {
>>>> diff --git a/src/nv_proto.h b/src/nv_proto.h
>>>> index 2e4fce0..2bd2ac7 100644
>>>> --- a/src/nv_proto.h
>>>> +++ b/src/nv_proto.h
>>>> @@ -7,7 +7,8 @@ void drmmode_adjust_frame(ScrnInfoPtr pScrn, int x,
>>>> int y, int flags);
>>>>   void drmmode_remove_fb(ScrnInfoPtr pScrn);
>>>>   Bool drmmode_cursor_init(ScreenPtr pScreen);
>>>>   void drmmode_fbcon_copy(ScreenPtr pScreen);
>>>> -Bool drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void
>>>> *priv);
>>>> +Bool drmmode_page_flip(DrawablePtr draw, PixmapPtr back, void *priv,
>>>> +		       unsigned int ref_crtc_hw_id);
>>>>   void drmmode_screen_init(ScreenPtr pScreen);
>>>>   void drmmode_screen_fini(ScreenPtr pScreen);
>>>>
>>>> @@ -26,6 +27,8 @@ Bool nouveau_allocate_surface(ScrnInfoPtr scrn,
>>>> int width, int height,
>>>>   void nouveau_dri2_vblank_handler(int fd, unsigned int frame,
>>>>   				 unsigned int tv_sec, unsigned int tv_usec,
>>>>   				 void *event_data);
>>>> +void nouveau_dri2_flip_event_handler(unsigned int frame, unsigned
>>>> int tv_sec,
>>>> +				     unsigned int tv_usec, void *event_data);
>>>>   Bool nouveau_dri2_init(ScreenPtr pScreen);
>>>>   void nouveau_dri2_fini(ScreenPtr pScreen);
>>
>> *********************************************************************
>> Mario Kleiner
>> Max Planck Institute for Biological Cybernetics
>> Spemannstr. 38
>> 72076 Tuebingen
>> Germany
>>
>> e-mail: mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org
>> office: +49 (0)7071/601-1623
>> fax:    +49 (0)7071/601-616
>> www:    http://www.kyb.tuebingen.mpg.de/~kleinerm
>> *********************************************************************
>> "For a successful technology, reality must take precedence
>> over public relations, for Nature cannot be fooled."
>> (Richard Feynman)

Re: [PATCH 1/3] dri2: Implement handling of pageflip completion events.

[Francisco Jerez]

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Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org> writes:

> On 09/09/2011 11:05 PM, Francisco Jerez wrote:
>> Mario Kleiner<mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org>  writes:
>>
>>>[...]
>>>
>>> Hi, thanks for the comments.
>>
>> Thank you for looking into this :)
>>>
>
> Sorry for the late reply. I'm a bit slow at the moment.
>
No worries, right now I have my mind somewhere else as well...

>>> I see your point, but at least as a starting point for the first
>>> iteration i don't think the current dri2 implementation of pageflips
>>> was a dumb decision.
>>>
>>> It is the same default "double buffer" behaviour that the binary
>>> drivers on Linux and also on other os'es (OS/X and Windows) expose.
>>
>> Not the nvidia one, last time I checked.
>>
>
> It doesn't neccessarily block glXXX drawing command submission, but it
> doesn't do triple-buffering by default. It blocks rendering until swap
> completion, probably just queueing up drawing commands internally.
>
I didn't mean it does (real) triple-buffering, but rather that it
doesn't block command submission to the new back buffer after
glXSwapBuffers() is called (which for most practical purposes gives a
similar effect to triple-buffering where the command buffer acts as
third buffer).

> Here is how my toolkit waits for swap completion with the binary blob
> on linux, os/x and windows:
>
> 1. glXSwapBuffers() (aka SwapBuffers() on Windows aka
> CGLFlushDrawable()) on OS/X).
>
> 2. glBegin(GL_POINTS); glVertex2i(10,10); glEnd();
> 3. glFinish();
> 4. Read clock, scanout position etc. compute swap completion
> timestamp.
>
> On any tested binary NVidia, ATI or Intel drivers on any tested
> Windows, OS/X or Linux version this blocks in glFinish() until swap
> completion, at least for page-flipped fullscreen swaps if the optional
> "triple buffering" option is not selected in the driver control
> panel. This method is successfully tested on multiple ten thousand
> users setups over at least the last six years.
>
> So glFinish() waits for draw completion and drawing apparently waits
> for swap completion - strictly double-buffered with the drivers
> default settings. Or at least the observable behaviour of the drivers
> is consistent with this assumption.
>
AFAICT you'd still get the same effect even if it were using something
different to double-buffering.

>>[...]
>> With the current implementation (and IIRC it's the same on both
>> radeon
>> and intel) the divisor/remainder relation is ignored in the case
>> where
>> the gpu is too busy to finish its rendering in time for the predicted
>> MSC; the flip is carried out as soon as the GPU finishes, possibly a
>> few
>> vblank periods later.
>>
>> To fix this properly in nouveau, I think it would be good to push the
>> divisor/remainder calculation down to the kernel (second reason so
>> far
>> to extend the kernel interface), but once it's done we'll get the
>> divisor/remainder relation right no matter if multibuffering is being
>> used or not.
>>
>
> Agreed on that. The current fix only fixes the easy case where the
> client submits a swap request too late to satisfy the
> divisor/remainder relation, or where the relation is easily
> satisfiable. E.g., my toolkit uses it to make sure that a swap happens
> after a user specified deadline, but only on, e.g., odd numbered video
> refresh cycles, for the purpose of getting frame-sequential stereo
> right.
>
> None of the current ddx handles the case where the backbuffer is still
> busy at the target vblank.
>
> Imho there are a couple of things a pageflip ioctl() v2 should
> provide:
>
> * Some support for frame-sequential stereo.
> * 64 bit target_msc.
> * Divisor/remainder in kernel.
>
Personally I'd like a more stupid pageflip IOCTL instead of a smarter
one... We could split the sync-to-vblank functionality into a different,
orthogonal IOCTL that:
 * takes a GEM object, a CRTC number, and a sync
   target/divisor/remainder.
 * makes sure that any further references (including command submission
   and page-flipping) to the given GEM object are synchronized to the
   given CRTC according to the given sync parameters.
 * optionally sends an event back to userspace once the
   sync target is reached.

This would get us a standard interface for:
 * Standard page-flipping respecting the divisor/remainder relation.
 * Tear-free multihead flipping (if done correctly).
 * Tear-free blitting with completion notification.
 * Tearful but fast non-vsync'ed pageflip.

>
>>[...]
>> IMHO getting a small (and required) fix (the swaplimit API) into one
>> software component is more advisable from the maintainership
>> standpoint
>> than putting in place two different codepaths in another software
>> component, both of which are broken in its own way.
>>
>
> I totally agree with you. But assume we finally manage to persuade
> Keith to integrate that API into 1.12, it would still be nice - at
> least for my users - if the nouveau ddx could optionally support a
> double-buffered mode with correct timestamps on current servers, e.g.,
> 1.9 - 1.11.
>
> I think the proposed patch should work for n-buffering on future
> servers with a swaplimit api, and for double-buffering with correct
> timestamping on current servers. For triple buffering on current
> servers it would be simple to add your current implementation back as
> a special case with only a few lines of code: Just don't request
> pageflip completion events from the kernel, so the whole pageflip
> callback gets skipped, and call DRI2SwapComplete() directly, as in the
> current ddx.
>
I don't think that the current n-buffering path will be necessary
anymore if the swaplimit patch is accepted - If anyone complains about a
performance regression on old X servers we can always tell him to turn
pageflip off.

> I think a x-org.conf option for selecting double-buffering /
> triple-buffering / n-buffering will be needed anyway, even with a
> swaplimit api in place, so we could add it now and use it to switch
> between double-buffering and n-buffering.
>
Yeah, we could add an integer option to let the user choose a swap
limit, but, keep in mind that settings different to "2" are very likely
to be useless for most people.

> I'm not really sure what Keith remaining objections to Paul's imho
> rather small, simple and well reviewed swaplimit api patch are, or if
> we just have some kind of miscommunication about what specific patch
> we were talking about. I will try to look at it again next week.
>
It seems he's been especially busy in the last few weeks...

> thanks,
> -mario
>[...]

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_______________________________________________
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[PATCH 2/3] dri2: Update front buffer pixmap and name before exchanging buffers

[Mario Kleiner]

Buffer exchange assumes that the front buffer pixmap and name
information is accurate. That may not be the case eg. if the window
has been (un)redirected since the buffer was created.

This is a translation to nouveau of a fix that was originally developed
by Ville Syrjala <syrjala-ORSVBvAovxo@public.gmane.org> for the ati/radeon ddx to fix the
same bug there.

See thread at:

http://lists.x.org/archives/xorg-devel/2011-May/021908.html

Signed-off-by: Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org>
---
 src/nouveau_dri2.c |   45 ++++++++++++++++++++++++++++++++++++++++++---
 1 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/src/nouveau_dri2.c b/src/nouveau_dri2.c
index 87eaf08..9f0ee97 100644
--- a/src/nouveau_dri2.c
+++ b/src/nouveau_dri2.c
@@ -140,6 +140,35 @@ struct nouveau_dri2_vblank_state {
 };
 
 static Bool
+update_front(DrawablePtr draw, DRI2BufferPtr front)
+{
+	int r;
+	PixmapPtr pixmap;
+	struct nouveau_dri2_buffer *nvbuf = nouveau_dri2_buffer(front);
+
+	if (draw->type == DRAWABLE_PIXMAP)
+		pixmap = (PixmapPtr)draw;
+	else
+		pixmap = (*draw->pScreen->GetWindowPixmap)((WindowPtr)draw);
+
+	pixmap->refcnt++;
+
+	exaMoveInPixmap(pixmap);
+	r = nouveau_bo_handle_get(nouveau_pixmap_bo(pixmap), &front->name);
+	if (r) {
+		(*draw->pScreen->DestroyPixmap)(pixmap);
+		return FALSE;
+	}
+
+	(*draw->pScreen->DestroyPixmap)(nvbuf->ppix);
+	front->pitch = pixmap->devKind;
+	front->cpp = pixmap->drawable.bitsPerPixel / 8;
+	nvbuf->ppix = pixmap;
+
+	return TRUE;
+}
+
+static Bool
 can_exchange(DrawablePtr draw, PixmapPtr dst_pix, PixmapPtr src_pix)
 {
 	ScrnInfoPtr scrn = xf86Screens[draw->pScreen->myNum];
@@ -212,13 +241,14 @@ nouveau_dri2_finish_swap(DrawablePtr draw, unsigned int frame,
 {
 	ScrnInfoPtr scrn = xf86Screens[draw->pScreen->myNum];
 	NVPtr pNv = NVPTR(scrn);
-	PixmapPtr dst_pix = nouveau_dri2_buffer(s->dst)->ppix;
+	PixmapPtr dst_pix;
 	PixmapPtr src_pix = nouveau_dri2_buffer(s->src)->ppix;
-	struct nouveau_bo *dst_bo = nouveau_pixmap_bo(dst_pix);
+	struct nouveau_bo *dst_bo;
 	struct nouveau_bo *src_bo = nouveau_pixmap_bo(src_pix);
 	struct nouveau_channel *chan = pNv->chan;
 	RegionRec reg;
 	int type, ret;
+	Bool front_updated;
 
 	REGION_INIT(0, &reg, (&(BoxRec){ 0, 0, draw->width, draw->height }), 0);
 	REGION_TRANSLATE(0, &reg, draw->x, draw->y);
@@ -235,6 +265,15 @@ nouveau_dri2_finish_swap(DrawablePtr draw, unsigned int frame,
 	if (ref_crtc_hw_id & 1)
 		ref_crtc_hw_id = 1;
 
+	/* Update frontbuffer pixmap and name: Could have changed due to
+	 * window (un)redirection as part of compositing.
+	 */
+	front_updated = update_front(draw, s->dst);
+
+	/* Assign frontbuffer pixmap, after update in update_front() */
+	dst_pix = nouveau_dri2_buffer(s->dst)->ppix;
+	dst_bo = nouveau_pixmap_bo(dst_pix);
+
 	/* Throttle on the previous frame before swapping */
 	nouveau_bo_map(dst_bo, NOUVEAU_BO_RD);
 	nouveau_bo_unmap(dst_bo);
@@ -253,7 +292,7 @@ nouveau_dri2_finish_swap(DrawablePtr draw, unsigned int frame,
 		FIRE_RING(chan);
 	}
 
-	if (can_exchange(draw, dst_pix, src_pix)) {
+	if (front_updated && can_exchange(draw, dst_pix, src_pix)) {
 		type = DRI2_EXCHANGE_COMPLETE;
 		DamageRegionAppend(draw, &reg);
 
-- 
1.7.1

[PATCH 3/3] dri2: Fixes to swap scheduling, especially for copy-swaps.

[Mario Kleiner]

Treats vblank event scheduling for the non-pageflip swap
case correctly. Allows vblank controlled swaps for redirected
windows. Fixes some corner-cases in OML_sync_control scheduling
when divisor and remainder parameters are used.

Signed-off-by: Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org>
---
 src/nouveau_dri2.c |   71 ++++++++++++++++++++++++++++++++++++++++++++-------
 1 files changed, 61 insertions(+), 10 deletions(-)

diff --git a/src/nouveau_dri2.c b/src/nouveau_dri2.c
index 9f0ee97..f14dea4 100644
--- a/src/nouveau_dri2.c
+++ b/src/nouveau_dri2.c
@@ -196,10 +196,8 @@ can_sync_to_vblank(DrawablePtr draw)
 {
 	ScrnInfoPtr scrn = xf86Screens[draw->pScreen->myNum];
 	NVPtr pNv = NVPTR(scrn);
-	PixmapPtr pix = NVGetDrawablePixmap(draw);
 
 	return pNv->glx_vblank &&
-		nouveau_exa_pixmap_is_onscreen(pix) &&
 		nv_window_belongs_to_crtc(scrn, draw->x, draw->y,
 					  draw->width, draw->height);
 }
@@ -344,9 +342,40 @@ nouveau_dri2_schedule_swap(ClientPtr client, DrawablePtr draw,
 			   CARD64 *target_msc, CARD64 divisor, CARD64 remainder,
 			   DRI2SwapEventPtr func, void *data)
 {
+	PixmapPtr dst_pix;
+	PixmapPtr src_pix = nouveau_dri2_buffer(src)->ppix;
 	struct nouveau_dri2_vblank_state *s;
 	CARD64 current_msc, expect_msc;
-	int ret;
+	int ret, flip = 0;
+	Bool front_updated;
+
+	/* Truncate to match kernel interfaces; means occasional overflow
+	 * misses, but that's generally not a big deal.
+	 */
+	*target_msc &= 0xffffffff;
+	divisor &= 0xffffffff;
+	remainder &= 0xffffffff;
+
+	/* Update frontbuffer pixmap and name: Could have changed due to
+	 * window (un)redirection as part of compositing.
+	 */
+	front_updated = update_front(draw, dst);
+
+	/* Assign frontbuffer pixmap, after update in update_front() */
+	dst_pix = nouveau_dri2_buffer(dst)->ppix;
+
+	/* Flips need to be submitted one frame before */
+	if (DRI2CanFlip(draw) && front_updated &&
+	    can_exchange(draw, dst_pix, src_pix)) {
+		flip = 1;
+	}
+
+	/* Correct target_msc by 'flip' if this is a page-flipped swap.
+	 * Do it early, so handling of different timing constraints
+	 * for divisor, remainder and msc vs. target_msc works.
+	 */
+	if (*target_msc > 0)
+		*target_msc -= (CARD64) flip;
 
 	/* Initialize a swap structure */
 	s = malloc(sizeof(*s));
@@ -363,19 +392,34 @@ nouveau_dri2_schedule_swap(ClientPtr client, DrawablePtr draw,
 		if (ret)
 			goto fail;
 
-		/* Calculate a swap target if we don't have one */
-		if (current_msc >= *target_msc && divisor)
+		/* Calculate a swap target if we don't have one or if
+		 * divisor/remainder relationship must be satisfied.
+		 */
+		if (current_msc >= *target_msc && divisor) {
 			*target_msc = current_msc + divisor
 				- (current_msc - remainder) % divisor;
 
-		/* Request a vblank event one frame before the target */
+			/* Account for extra pageflip delay if flip > 0 */
+			*target_msc -= (CARD64) flip;
+		}
+
+		/* Request a vblank event one frame before the target, unless
+		 * this is a copy-swap, in which case we need to make sure
+		 * it is only dispatched at the target frame or later.
+		 */
 		ret = nouveau_wait_vblank(draw, DRM_VBLANK_ABSOLUTE |
-					  DRM_VBLANK_EVENT,
-					  max(current_msc, *target_msc - 1),
+					  DRM_VBLANK_EVENT |
+					  ((flip) ? 0 : DRM_VBLANK_NEXTONMISS),
+					  max(current_msc, *target_msc),
 					  &expect_msc, NULL, s);
 		if (ret)
 			goto fail;
-		s->frame = (unsigned int) expect_msc & 0xffffffff;
+
+		/* Store expected target_msc for later consistency check and
+		 * return it to server for proper swap_interval implementation.
+		 */
+		s->frame = ((unsigned int) (expect_msc & 0xffffffff)) + flip ;
+		*target_msc = s->frame;
 	} else {
 		/* We can't/don't want to sync to vblank, just swap. */
 		nouveau_dri2_finish_swap(draw, 0, 0, 0, s);
@@ -396,6 +440,13 @@ nouveau_dri2_schedule_wait(ClientPtr client, DrawablePtr draw,
 	CARD64 current_msc;
 	int ret;
 
+	/* Truncate to match kernel interfaces; means occasional overflow
+	 * misses, but that's generally not a big deal.
+	 */
+	target_msc &= 0xffffffff;
+	divisor &= 0xffffffff;
+	remainder &= 0xffffffff;
+
 	if (!can_sync_to_vblank(draw)) {
 		DRI2WaitMSCComplete(client, draw, target_msc, 0, 0);
 		return TRUE;
@@ -415,7 +466,7 @@ nouveau_dri2_schedule_wait(ClientPtr client, DrawablePtr draw,
 		goto fail;
 
 	/* Calculate a wait target if we don't have one */
-	if (current_msc > target_msc && divisor)
+	if (current_msc >= target_msc && divisor)
 		target_msc = current_msc + divisor
 			- (current_msc - remainder) % divisor;
 
-- 
1.7.1

Re: [PATCH 3/3] dri2: Fixes to swap scheduling, especially for copy-swaps.

[Francisco Jerez]

[-- Attachment #1.1.1: Type: text/plain, Size: 5981 bytes --]

Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org> writes:

> Treats vblank event scheduling for the non-pageflip swap
> case correctly. Allows vblank controlled swaps for redirected
> windows. Fixes some corner-cases in OML_sync_control scheduling
> when divisor and remainder parameters are used.
>
> Signed-off-by: Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org>
> ---
>  src/nouveau_dri2.c |   71 ++++++++++++++++++++++++++++++++++++++++++++-------
>  1 files changed, 61 insertions(+), 10 deletions(-)
>
> diff --git a/src/nouveau_dri2.c b/src/nouveau_dri2.c
> index 9f0ee97..f14dea4 100644
> --- a/src/nouveau_dri2.c
> +++ b/src/nouveau_dri2.c
> @@ -196,10 +196,8 @@ can_sync_to_vblank(DrawablePtr draw)
>  {
>  	ScrnInfoPtr scrn = xf86Screens[draw->pScreen->myNum];
>  	NVPtr pNv = NVPTR(scrn);
> -	PixmapPtr pix = NVGetDrawablePixmap(draw);
>  
>  	return pNv->glx_vblank &&
> -		nouveau_exa_pixmap_is_onscreen(pix) &&

I'm not sure that this is the right way to fix this problem, depending
on the kind of transformations that the compositing manager is doing
you're likely to end up picking a CRTC at random... I just have the
impression that for redirected windows syncing to vblank is no longer
our responsibility, but rather the compositing manager's.

>  		nv_window_belongs_to_crtc(scrn, draw->x, draw->y,
>  					  draw->width, draw->height);
>  }
> @@ -344,9 +342,40 @@ nouveau_dri2_schedule_swap(ClientPtr client, DrawablePtr draw,
>  			   CARD64 *target_msc, CARD64 divisor, CARD64 remainder,
>  			   DRI2SwapEventPtr func, void *data)
>  {
> +	PixmapPtr dst_pix;
> +	PixmapPtr src_pix = nouveau_dri2_buffer(src)->ppix;
>  	struct nouveau_dri2_vblank_state *s;
>  	CARD64 current_msc, expect_msc;
> -	int ret;
> +	int ret, flip = 0;
> +	Bool front_updated;
> +
> +	/* Truncate to match kernel interfaces; means occasional overflow
> +	 * misses, but that's generally not a big deal.
> +	 */
> +	*target_msc &= 0xffffffff;
> +	divisor &= 0xffffffff;
> +	remainder &= 0xffffffff;
> +
This doesn't really fix the problem with our 32bit counters wrapping
around, but, as the comment says, it's not a big deal...

> +	/* Update frontbuffer pixmap and name: Could have changed due to
> +	 * window (un)redirection as part of compositing.
> +	 */
> +	front_updated = update_front(draw, dst);
> +
> +	/* Assign frontbuffer pixmap, after update in update_front() */
> +	dst_pix = nouveau_dri2_buffer(dst)->ppix;
> +
> +	/* Flips need to be submitted one frame before */
> +	if (DRI2CanFlip(draw) && front_updated &&
> +	    can_exchange(draw, dst_pix, src_pix)) {
> +		flip = 1;
> +	}
> +
> +	/* Correct target_msc by 'flip' if this is a page-flipped swap.
> +	 * Do it early, so handling of different timing constraints
> +	 * for divisor, remainder and msc vs. target_msc works.
> +	 */
> +	if (*target_msc > 0)
> +		*target_msc -= (CARD64) flip;

We don't need the code above, blits are submitted one frame before as
well - the wait for the final vblank is done in hardware by the GPU
itself, that way we don't have to worry about tearing caused by the GPU
being too busy to finish all its previous work in time for the specified
vblank interval.

>  
>  	/* Initialize a swap structure */
>  	s = malloc(sizeof(*s));
> @@ -363,19 +392,34 @@ nouveau_dri2_schedule_swap(ClientPtr client, DrawablePtr draw,
>  		if (ret)
>  			goto fail;
>  
> -		/* Calculate a swap target if we don't have one */
> -		if (current_msc >= *target_msc && divisor)
> +		/* Calculate a swap target if we don't have one or if
> +		 * divisor/remainder relationship must be satisfied.
> +		 */
Hm, the divisor/remainder relationship having to be satisfied is just
what one has to do when "we don't have one".

> +		if (current_msc >= *target_msc && divisor) {
>  			*target_msc = current_msc + divisor
>  				- (current_msc - remainder) % divisor;
>  
> -		/* Request a vblank event one frame before the target */
> +			/* Account for extra pageflip delay if flip > 0 */
> +			*target_msc -= (CARD64) flip;
> +		}
> +
> +		/* Request a vblank event one frame before the target, unless
> +		 * this is a copy-swap, in which case we need to make sure
> +		 * it is only dispatched at the target frame or later.
> +		 */
>  		ret = nouveau_wait_vblank(draw, DRM_VBLANK_ABSOLUTE |
> -					  DRM_VBLANK_EVENT,
> -					  max(current_msc, *target_msc - 1),
> +					  DRM_VBLANK_EVENT |
> +					  ((flip) ? 0 : DRM_VBLANK_NEXTONMISS),
> +					  max(current_msc, *target_msc),
>  					  &expect_msc, NULL, s);
>  		if (ret)
>  			goto fail;
> -		s->frame = (unsigned int) expect_msc & 0xffffffff;
> +
> +		/* Store expected target_msc for later consistency check and
> +		 * return it to server for proper swap_interval implementation.
> +		 */
> +		s->frame = ((unsigned int) (expect_msc & 0xffffffff)) + flip ;
> +		*target_msc = s->frame;

No need for this, same comment as above.

>  	} else {
>  		/* We can't/don't want to sync to vblank, just swap. */
>  		nouveau_dri2_finish_swap(draw, 0, 0, 0, s);
> @@ -396,6 +440,13 @@ nouveau_dri2_schedule_wait(ClientPtr client, DrawablePtr draw,
>  	CARD64 current_msc;
>  	int ret;
>  
> +	/* Truncate to match kernel interfaces; means occasional overflow
> +	 * misses, but that's generally not a big deal.
> +	 */
> +	target_msc &= 0xffffffff;
> +	divisor &= 0xffffffff;
> +	remainder &= 0xffffffff;
> +
>  	if (!can_sync_to_vblank(draw)) {
>  		DRI2WaitMSCComplete(client, draw, target_msc, 0, 0);
>  		return TRUE;
> @@ -415,7 +466,7 @@ nouveau_dri2_schedule_wait(ClientPtr client, DrawablePtr draw,
>  		goto fail;
>  
>  	/* Calculate a wait target if we don't have one */
> -	if (current_msc > target_msc && divisor)
> +	if (current_msc >= target_msc && divisor)
>  		target_msc = current_msc + divisor
>  			- (current_msc - remainder) % divisor;

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[-- Attachment #2: Type: text/plain, Size: 181 bytes --]

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Re: [PATCH 3/3] dri2: Fixes to swap scheduling, especially for copy-swaps.

[Mario Kleiner]

On Sep 8, 2011, at 1:00 AM, Francisco Jerez wrote:

Thanks for your review. See comments below.

> Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org> writes:
>
>> Treats vblank event scheduling for the non-pageflip swap
>> case correctly. Allows vblank controlled swaps for redirected
>> windows. Fixes some corner-cases in OML_sync_control scheduling
>> when divisor and remainder parameters are used.
>>
>> Signed-off-by: Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org>
>> ---
>>  src/nouveau_dri2.c |   71 ++++++++++++++++++++++++++++++++++++++++ 
>> ++++-------
>>  1 files changed, 61 insertions(+), 10 deletions(-)
>>
>> diff --git a/src/nouveau_dri2.c b/src/nouveau_dri2.c
>> index 9f0ee97..f14dea4 100644
>> --- a/src/nouveau_dri2.c
>> +++ b/src/nouveau_dri2.c
>> @@ -196,10 +196,8 @@ can_sync_to_vblank(DrawablePtr draw)
>>  {
>>  	ScrnInfoPtr scrn = xf86Screens[draw->pScreen->myNum];
>>  	NVPtr pNv = NVPTR(scrn);
>> -	PixmapPtr pix = NVGetDrawablePixmap(draw);
>>
>>  	return pNv->glx_vblank &&
>> -		nouveau_exa_pixmap_is_onscreen(pix) &&
>
> I'm not sure that this is the right way to fix this problem, depending
> on the kind of transformations that the compositing manager is doing
> you're likely to end up picking a CRTC at random... I just have the
> impression that for redirected windows syncing to vblank is no longer
> our responsibility, but rather the compositing manager's.
>

I don't think it is the perfect way either, but to me it seems to be  
some improvement for the time being. Ideally there would be protocol  
probably between the compositor and mesa to get this perfectly right  
- translate the oml_sync_control and classic glXSwapBuffers requests  
into some requests for the compositor and x-server.

But the current implementation under a compositor is not great. You  
get glxgears reporting that "vsync is on and the redraw rate should  
equal the refresh rate" but see 2900 fps reported on a 60 Hz display,  
with apparently 60 Hz animation. And, in my use case, toolkits that  
care about timing and do some consistency checks on their swapbuffers  
execution bail out immediately, telling you to fix your "totally  
broken graphics driver setup".

It's a pure "better than nothing" change for the redirected case,  
which seems to behave less confusing, at least as no fancy  
transformations are used, e.g., during desktop transitions.

Some consistent crtc selection is another thing that imho would need  
a bit of work for nouveau and the other drivers. Currently nouveau  
always selects the 1st crtc for vblank events based swap scheduling  
and vsync if a window spans multiple displays on xinerama setups,  
regardless if a non-fullscreen window is displaying on the first or  
second monitor. Same goes for fullscreen drawables, regardless of how  
much area is covered by the viewport of a crtc. The other drivers  
select the crtc to sync by the intersection area of drawable and  
crtc, so tearing fuer multi-display spanning windows is limited to  
the "smaller display". It also makes sense to give users some control  
over this for clone mode, e.g., when they give a presentation and  
don't care if their laptops flat panel tears, but don't want tearing  
on the presentation screen for the audience. E.g., one could prefer  
the --primary output as defined by xrandr.

>>  		nv_window_belongs_to_crtc(scrn, draw->x, draw->y,
>>  					  draw->width, draw->height);
>>  }
>> @@ -344,9 +342,40 @@ nouveau_dri2_schedule_swap(ClientPtr client,  
>> DrawablePtr draw,
>>  			   CARD64 *target_msc, CARD64 divisor, CARD64 remainder,
>>  			   DRI2SwapEventPtr func, void *data)
>>  {
>> +	PixmapPtr dst_pix;
>> +	PixmapPtr src_pix = nouveau_dri2_buffer(src)->ppix;
>>  	struct nouveau_dri2_vblank_state *s;
>>  	CARD64 current_msc, expect_msc;
>> -	int ret;
>> +	int ret, flip = 0;
>> +	Bool front_updated;
>> +
>> +	/* Truncate to match kernel interfaces; means occasional overflow
>> +	 * misses, but that's generally not a big deal.
>> +	 */
>> +	*target_msc &= 0xffffffff;
>> +	divisor &= 0xffffffff;
>> +	remainder &= 0xffffffff;
>> +
> This doesn't really fix the problem with our 32bit counters wrapping
> around, but, as the comment says, it's not a big deal...
>

Yes. Another item, get 64-bit counters and api for the kernel drm.  
Mostly to make explicit that there is a 32-bit limit in place.

>> +	/* Update frontbuffer pixmap and name: Could have changed due to
>> +	 * window (un)redirection as part of compositing.
>> +	 */
>> +	front_updated = update_front(draw, dst);
>> +
>> +	/* Assign frontbuffer pixmap, after update in update_front() */
>> +	dst_pix = nouveau_dri2_buffer(dst)->ppix;
>> +
>> +	/* Flips need to be submitted one frame before */
>> +	if (DRI2CanFlip(draw) && front_updated &&
>> +	    can_exchange(draw, dst_pix, src_pix)) {
>> +		flip = 1;
>> +	}
>> +
>> +	/* Correct target_msc by 'flip' if this is a page-flipped swap.
>> +	 * Do it early, so handling of different timing constraints
>> +	 * for divisor, remainder and msc vs. target_msc works.
>> +	 */
>> +	if (*target_msc > 0)
>> +		*target_msc -= (CARD64) flip;
>
> We don't need the code above, blits are submitted one frame before as
> well - the wait for the final vblank is done in hardware by the GPU
> itself, that way we don't have to worry about tearing caused by the  
> GPU
> being too busy to finish all its previous work in time for the  
> specified
> vblank interval.
>

Oh ok, thanks. I have special measurement equipment here to test  
pageflipped swaps for timing, but can't test the copyswap case  
easily. My toolkit was complaining loudly about inconsistencies, so i  
was just assuming it is due to the same logic as on other gpu's +  
missing code in the ddx. If copy-swaps are intentionally scheduled  
one frame ahead, then DRI2SwapComplete timestamps would need to be  
corrected for that. Currently you get the puzzling result from the  
timestamps that swaps complete before they were even scheduled by the  
client, typically a clear indication of broken vsync support in the  
driver.

Do you know how this is done at the hardware level? Exactly as with  
pageflips? The gpu programming seems to be the same in the ddx. Is  
the blip operation started at leading edge of the vblank interval? Or  
anywhere inside the vblank interval (level triggered)? Are such blits  
submitted on a separate fifo (or even dma engine?) in the gpu to  
avoid stalling the rest of the command stream until vblank?


>>
>>  	/* Initialize a swap structure */
>>  	s = malloc(sizeof(*s));
>> @@ -363,19 +392,34 @@ nouveau_dri2_schedule_swap(ClientPtr client,  
>> DrawablePtr draw,
>>  		if (ret)
>>  			goto fail;
>>
>> -		/* Calculate a swap target if we don't have one */
>> -		if (current_msc >= *target_msc && divisor)
>> +		/* Calculate a swap target if we don't have one or if
>> +		 * divisor/remainder relationship must be satisfied.
>> +		 */
> Hm, the divisor/remainder relationship having to be satisfied is just
> what one has to do when "we don't have one".

Technically, if the target_msc is already reached/exceeded and we  
have divisor/remainder. "we don't have one" == "target_msc == 0" is a  
very common special case of this. Just wanted to clarify, as i  
understood "we don't have one" as target_msc == 0. Not sure if my new  
comment is much better, just that i was a bit confused on first read.

>> +		if (current_msc >= *target_msc && divisor) {
>>  			*target_msc = current_msc + divisor
>>  				- (current_msc - remainder) % divisor;
>>
>> -		/* Request a vblank event one frame before the target */
>> +			/* Account for extra pageflip delay if flip > 0 */
>> +			*target_msc -= (CARD64) flip;
>> +		}
>> +
>> +		/* Request a vblank event one frame before the target, unless
>> +		 * this is a copy-swap, in which case we need to make sure
>> +		 * it is only dispatched at the target frame or later.
>> +		 */
>>  		ret = nouveau_wait_vblank(draw, DRM_VBLANK_ABSOLUTE |
>> -					  DRM_VBLANK_EVENT,
>> -					  max(current_msc, *target_msc - 1),
>> +					  DRM_VBLANK_EVENT |
>> +					  ((flip) ? 0 : DRM_VBLANK_NEXTONMISS),
>> +					  max(current_msc, *target_msc),
>>  					  &expect_msc, NULL, s);
>>  		if (ret)
>>  			goto fail;
>> -		s->frame = (unsigned int) expect_msc & 0xffffffff;
>> +
>> +		/* Store expected target_msc for later consistency check and
>> +		 * return it to server for proper swap_interval implementation.
>> +		 */
>> +		s->frame = ((unsigned int) (expect_msc & 0xffffffff)) + flip ;
>> +		*target_msc = s->frame;
>
> No need for this, same comment as above.
>

Ok.

>>  	} else {
>>  		/* We can't/don't want to sync to vblank, just swap. */
>>  		nouveau_dri2_finish_swap(draw, 0, 0, 0, s);
>> @@ -396,6 +440,13 @@ nouveau_dri2_schedule_wait(ClientPtr client,  
>> DrawablePtr draw,
>>  	CARD64 current_msc;
>>  	int ret;
>>
>> +	/* Truncate to match kernel interfaces; means occasional overflow
>> +	 * misses, but that's generally not a big deal.
>> +	 */
>> +	target_msc &= 0xffffffff;
>> +	divisor &= 0xffffffff;
>> +	remainder &= 0xffffffff;
>> +
>>  	if (!can_sync_to_vblank(draw)) {
>>  		DRI2WaitMSCComplete(client, draw, target_msc, 0, 0);
>>  		return TRUE;
>> @@ -415,7 +466,7 @@ nouveau_dri2_schedule_wait(ClientPtr client,  
>> DrawablePtr draw,
>>  		goto fail;
>>
>>  	/* Calculate a wait target if we don't have one */
>> -	if (current_msc > target_msc && divisor)
>> +	if (current_msc >= target_msc && divisor)
>>  		target_msc = current_msc + divisor
>>  			- (current_msc - remainder) % divisor;

*********************************************************************
Mario Kleiner
Max Planck Institute for Biological Cybernetics
Spemannstr. 38
72076 Tuebingen
Germany

e-mail: mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org
office: +49 (0)7071/601-1623
fax:    +49 (0)7071/601-616
www:    http://www.kyb.tuebingen.mpg.de/~kleinerm
*********************************************************************
"For a successful technology, reality must take precedence
over public relations, for Nature cannot be fooled."
(Richard Feynman)

Re: [PATCH 3/3] dri2: Fixes to swap scheduling, especially for copy-swaps.

[Francisco Jerez]

[-- Attachment #1.1.1: Type: text/plain, Size: 12171 bytes --]

Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org> writes:

> On Sep 8, 2011, at 1:00 AM, Francisco Jerez wrote:
>
> Thanks for your review. See comments below.
>
>> Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org> writes:
>>
>>> Treats vblank event scheduling for the non-pageflip swap
>>> case correctly. Allows vblank controlled swaps for redirected
>>> windows. Fixes some corner-cases in OML_sync_control scheduling
>>> when divisor and remainder parameters are used.
>>>
>>> Signed-off-by: Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org>
>>> ---
>>>  src/nouveau_dri2.c |   71 ++++++++++++++++++++++++++++++++++++++++
>>> ++++-------
>>>  1 files changed, 61 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/src/nouveau_dri2.c b/src/nouveau_dri2.c
>>> index 9f0ee97..f14dea4 100644
>>> --- a/src/nouveau_dri2.c
>>> +++ b/src/nouveau_dri2.c
>>> @@ -196,10 +196,8 @@ can_sync_to_vblank(DrawablePtr draw)
>>>  {
>>>  	ScrnInfoPtr scrn = xf86Screens[draw->pScreen->myNum];
>>>  	NVPtr pNv = NVPTR(scrn);
>>> -	PixmapPtr pix = NVGetDrawablePixmap(draw);
>>>
>>>  	return pNv->glx_vblank &&
>>> -		nouveau_exa_pixmap_is_onscreen(pix) &&
>>
>> I'm not sure that this is the right way to fix this problem, depending
>> on the kind of transformations that the compositing manager is doing
>> you're likely to end up picking a CRTC at random... I just have the
>> impression that for redirected windows syncing to vblank is no longer
>> our responsibility, but rather the compositing manager's.
>>
>
> I don't think it is the perfect way either, but to me it seems to be
> some improvement for the time being. Ideally there would be protocol
> probably between the compositor and mesa to get this perfectly right -
> translate the oml_sync_control and classic glXSwapBuffers requests
> into some requests for the compositor and x-server.
>
I'm not sure the spec itself makes that much sense when you're running a
compositing manager... Anyway I suspect there's a common fix for this
and the synchronization issue we had with the "exchange" swapbuffers
path, that only involves some minor rewording in the DRI2 protocol.

> But the current implementation under a compositor is not great. You
> get glxgears reporting that "vsync is on and the redraw rate should
> equal the refresh rate" but see 2900 fps reported on a 60 Hz display,
> with apparently 60 Hz animation. And, in my use case, toolkits that
> care about timing and do some consistency checks on their swapbuffers
> execution bail out immediately, telling you to fix your "totally
> broken graphics driver setup".
>
> It's a pure "better than nothing" change for the redirected case,
> which seems to behave less confusing, at least as no fancy
> transformations are used, e.g., during desktop transitions.
>
OK, fair enough.

> Some consistent crtc selection is another thing that imho would need a
> bit of work for nouveau and the other drivers. Currently nouveau
> always selects the 1st crtc for vblank events based swap scheduling
> and vsync if a window spans multiple displays on xinerama setups,
> regardless if a non-fullscreen window is displaying on the first or
> second monitor. Same goes for fullscreen drawables, regardless of how
> much area is covered by the viewport of a crtc. The other drivers
> select the crtc to sync by the intersection area of drawable and
> crtc, so tearing fuer multi-display spanning windows is limited to
> the "smaller display". It also makes sense to give users some control
> over this for clone mode, e.g., when they give a presentation and
> don't care if their laptops flat panel tears, but don't want tearing
> on the presentation screen for the audience. E.g., one could prefer
> the --primary output as defined by xrandr.
>
>>>  		nv_window_belongs_to_crtc(scrn, draw->x, draw->y,
>>>  					  draw->width, draw->height);
>>>  }
>>> @@ -344,9 +342,40 @@ nouveau_dri2_schedule_swap(ClientPtr client,
>>> DrawablePtr draw,
>>>  			   CARD64 *target_msc, CARD64 divisor, CARD64 remainder,
>>>  			   DRI2SwapEventPtr func, void *data)
>>>  {
>>> +	PixmapPtr dst_pix;
>>> +	PixmapPtr src_pix = nouveau_dri2_buffer(src)->ppix;
>>>  	struct nouveau_dri2_vblank_state *s;
>>>  	CARD64 current_msc, expect_msc;
>>> -	int ret;
>>> +	int ret, flip = 0;
>>> +	Bool front_updated;
>>> +
>>> +	/* Truncate to match kernel interfaces; means occasional overflow
>>> +	 * misses, but that's generally not a big deal.
>>> +	 */
>>> +	*target_msc &= 0xffffffff;
>>> +	divisor &= 0xffffffff;
>>> +	remainder &= 0xffffffff;
>>> +
>> This doesn't really fix the problem with our 32bit counters wrapping
>> around, but, as the comment says, it's not a big deal...
>>
>
> Yes. Another item, get 64-bit counters and api for the kernel
> drm. Mostly to make explicit that there is a 32-bit limit in place.
>
>>> +	/* Update frontbuffer pixmap and name: Could have changed due to
>>> +	 * window (un)redirection as part of compositing.
>>> +	 */
>>> +	front_updated = update_front(draw, dst);
>>> +
>>> +	/* Assign frontbuffer pixmap, after update in update_front() */
>>> +	dst_pix = nouveau_dri2_buffer(dst)->ppix;
>>> +
>>> +	/* Flips need to be submitted one frame before */
>>> +	if (DRI2CanFlip(draw) && front_updated &&
>>> +	    can_exchange(draw, dst_pix, src_pix)) {
>>> +		flip = 1;
>>> +	}
>>> +
>>> +	/* Correct target_msc by 'flip' if this is a page-flipped swap.
>>> +	 * Do it early, so handling of different timing constraints
>>> +	 * for divisor, remainder and msc vs. target_msc works.
>>> +	 */
>>> +	if (*target_msc > 0)
>>> +		*target_msc -= (CARD64) flip;
>>
>> We don't need the code above, blits are submitted one frame before as
>> well - the wait for the final vblank is done in hardware by the GPU
>> itself, that way we don't have to worry about tearing caused by the
>> GPU
>> being too busy to finish all its previous work in time for the
>> specified
>> vblank interval.
>>
>
> Oh ok, thanks. I have special measurement equipment here to test
> pageflipped swaps for timing, but can't test the copyswap case
> easily. My toolkit was complaining loudly about inconsistencies, so i
> was just assuming it is due to the same logic as on other gpu's +
> missing code in the ddx. If copy-swaps are intentionally scheduled
> one frame ahead, then DRI2SwapComplete timestamps would need to be
> corrected for that. Currently you get the puzzling result from the
> timestamps that swaps complete before they were even scheduled by the
> client, typically a clear indication of broken vsync support in the
> driver.
>
Heh, yeah...

> Do you know how this is done at the hardware level? Exactly as with
> pageflips? The gpu programming seems to be the same in the ddx.

Yes, we use the same synchronization mechanism for pageflips and blits.

> Is the blip operation started at leading edge of the vblank interval?
> Or anywhere inside the vblank interval (level triggered)? Are such
> blits submitted on a separate fifo (or even dma engine?) in the gpu to
> avoid stalling the rest of the command stream until vblank?

It depends, right now we have two completely different implementations
and we use one or the other depending on the card generation:

On nv11-nv4x, we use the PGRAPH vsync methods (0x120-0x134), that means
it's the drawing engine that waits. Basically you have a counter that's
incremented by a CRTC of your choice when it reaches a scanline range of
your choice, wrapping around at a configurable value; you can put the
drawing engine to sleep until the counter reaches a given value. Right
now we make it wait until somewhere between vdisplay-3 and vdisplay-1
before going on with the swap.

From nv5x on, we use PFIFO semaphores to suspend the execution of the
channel (right now the main X server channel but this could be changed)
until a pre-allocated memory location gets a given value, which is
written there manually by the PDISPLAY vblank interrupt handler. I'm not
sure when exactly this IRQ happens, most likely it can be configured,
but I have reasons to believe that in some set-ups it happens at the
end of the vblank period causing the tearing I've seen a few times.

>
>
>>>
>>>  	/* Initialize a swap structure */
>>>  	s = malloc(sizeof(*s));
>>> @@ -363,19 +392,34 @@ nouveau_dri2_schedule_swap(ClientPtr client,
>>> DrawablePtr draw,
>>>  		if (ret)
>>>  			goto fail;
>>>
>>> -		/* Calculate a swap target if we don't have one */
>>> -		if (current_msc >= *target_msc && divisor)
>>> +		/* Calculate a swap target if we don't have one or if
>>> +		 * divisor/remainder relationship must be satisfied.
>>> +		 */
>> Hm, the divisor/remainder relationship having to be satisfied is just
>> what one has to do when "we don't have one".
>
> Technically, if the target_msc is already reached/exceeded and we have
> divisor/remainder. "we don't have one" == "target_msc == 0" is a  very
> common special case of this. Just wanted to clarify, as i  understood
> "we don't have one" as target_msc == 0. Not sure if my new  comment is
> much better, just that i was a bit confused on first read.
>
>>> +		if (current_msc >= *target_msc && divisor) {
>>>  			*target_msc = current_msc + divisor
>>>  				- (current_msc - remainder) % divisor;
>>>
>>> -		/* Request a vblank event one frame before the target */
>>> +			/* Account for extra pageflip delay if flip > 0 */
>>> +			*target_msc -= (CARD64) flip;
>>> +		}
>>> +
>>> +		/* Request a vblank event one frame before the target, unless
>>> +		 * this is a copy-swap, in which case we need to make sure
>>> +		 * it is only dispatched at the target frame or later.
>>> +		 */
>>>  		ret = nouveau_wait_vblank(draw, DRM_VBLANK_ABSOLUTE |
>>> -					  DRM_VBLANK_EVENT,
>>> -					  max(current_msc, *target_msc - 1),
>>> +					  DRM_VBLANK_EVENT |
>>> +					  ((flip) ? 0 : DRM_VBLANK_NEXTONMISS),
>>> +					  max(current_msc, *target_msc),
>>>  					  &expect_msc, NULL, s);
>>>  		if (ret)
>>>  			goto fail;
>>> -		s->frame = (unsigned int) expect_msc & 0xffffffff;
>>> +
>>> +		/* Store expected target_msc for later consistency check and
>>> +		 * return it to server for proper swap_interval implementation.
>>> +		 */
>>> +		s->frame = ((unsigned int) (expect_msc & 0xffffffff)) + flip ;
>>> +		*target_msc = s->frame;
>>
>> No need for this, same comment as above.
>>
>
> Ok.
>
>>>  	} else {
>>>  		/* We can't/don't want to sync to vblank, just swap. */
>>>  		nouveau_dri2_finish_swap(draw, 0, 0, 0, s);
>>> @@ -396,6 +440,13 @@ nouveau_dri2_schedule_wait(ClientPtr client,
>>> DrawablePtr draw,
>>>  	CARD64 current_msc;
>>>  	int ret;
>>>
>>> +	/* Truncate to match kernel interfaces; means occasional overflow
>>> +	 * misses, but that's generally not a big deal.
>>> +	 */
>>> +	target_msc &= 0xffffffff;
>>> +	divisor &= 0xffffffff;
>>> +	remainder &= 0xffffffff;
>>> +
>>>  	if (!can_sync_to_vblank(draw)) {
>>>  		DRI2WaitMSCComplete(client, draw, target_msc, 0, 0);
>>>  		return TRUE;
>>> @@ -415,7 +466,7 @@ nouveau_dri2_schedule_wait(ClientPtr client,
>>> DrawablePtr draw,
>>>  		goto fail;
>>>
>>>  	/* Calculate a wait target if we don't have one */
>>> -	if (current_msc > target_msc && divisor)
>>> +	if (current_msc >= target_msc && divisor)
>>>  		target_msc = current_msc + divisor
>>>  			- (current_msc - remainder) % divisor;
>
> *********************************************************************
> Mario Kleiner
> Max Planck Institute for Biological Cybernetics
> Spemannstr. 38
> 72076 Tuebingen
> Germany
>
> e-mail: mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org
> office: +49 (0)7071/601-1623
> fax:    +49 (0)7071/601-616
> www:    http://www.kyb.tuebingen.mpg.de/~kleinerm
> *********************************************************************
> "For a successful technology, reality must take precedence
> over public relations, for Nature cannot be fooled."
> (Richard Feynman)

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Re: [PATCH 3/3] dri2: Fixes to swap scheduling, especially for copy-swaps.

[Mario Kleiner]

On 09/09/2011 11:14 PM, Francisco Jerez wrote:
> Mario Kleiner<mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org>  writes:
>
>> On Sep 8, 2011, at 1:00 AM, Francisco Jerez wrote:
>>
>> Thanks for your review. See comments below.
>>
>>> Mario Kleiner<mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org>  writes:
>>>
>>>> Treats vblank event scheduling for the non-pageflip swap
>>>> case correctly. Allows vblank controlled swaps for redirected
>>>> windows. Fixes some corner-cases in OML_sync_control scheduling
>>>> when divisor and remainder parameters are used.
>>>>
>>>> Signed-off-by: Mario Kleiner<mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org>
>>>> ---
>>>>   src/nouveau_dri2.c |   71 ++++++++++++++++++++++++++++++++++++++++
>>>> ++++-------
>>>>   1 files changed, 61 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/src/nouveau_dri2.c b/src/nouveau_dri2.c
>>>> index 9f0ee97..f14dea4 100644
>>>> --- a/src/nouveau_dri2.c
>>>> +++ b/src/nouveau_dri2.c
>>>> @@ -196,10 +196,8 @@ can_sync_to_vblank(DrawablePtr draw)
>>>>   {
>>>>   	ScrnInfoPtr scrn = xf86Screens[draw->pScreen->myNum];
>>>>   	NVPtr pNv = NVPTR(scrn);
>>>> -	PixmapPtr pix = NVGetDrawablePixmap(draw);
>>>>
>>>>   	return pNv->glx_vblank&&
>>>> -		nouveau_exa_pixmap_is_onscreen(pix)&&
>>>
>>> I'm not sure that this is the right way to fix this problem, depending
>>> on the kind of transformations that the compositing manager is doing
>>> you're likely to end up picking a CRTC at random... I just have the
>>> impression that for redirected windows syncing to vblank is no longer
>>> our responsibility, but rather the compositing manager's.
>>>
>>
>> I don't think it is the perfect way either, but to me it seems to be
>> some improvement for the time being. Ideally there would be protocol
>> probably between the compositor and mesa to get this perfectly right -
>> translate the oml_sync_control and classic glXSwapBuffers requests
>> into some requests for the compositor and x-server.
>>
> I'm not sure the spec itself makes that much sense when you're running a
> compositing manager... Anyway I suspect there's a common fix for this
> and the synchronization issue we had with the "exchange" swapbuffers
> path, that only involves some minor rewording in the DRI2 protocol.
>

Afaik the oml_sync_control spec is based on some sgi spec for their 
former big multi-pipe machines (Onyx Infinite Reality engine and such), 
where you had multiple displays, but they were usually driven with 
exactly the same video modes in perfect sync, always acting like one big 
single x-screen. That shows through in some places i think.

But the spec itself should still make sense with composition manager. It 
"just" requires quite a bit of extra protocol and effort for 
unredirected windows if one wants to do it properly, as far as i can 
see. Basically send the whole dri2swapbuffers request to the compositor, 
get some acknowledge from it when it is safe to exchange the buffers and 
then the compositor would need to schedule and send swaprequests itself, 
according to the (target_msc, divisor, remainder) and would also need to 
call dri2swapcomplete when the swap is actually done. Probably these 
interactions should rather happen between mesa <-> compositor <-> 
x-server/ddx rather than mesa <-> x-server <-> ddx <-> compositor. But 
the spec itself - the api from the viewpoint of the gl client - would 
still make a lot of sense imho.

There were some plans on this on the 
<http://dri.freedesktop.org/wiki/CompositeSwap> Wiki.

>> But the current implementation under a compositor is not great. You
>> get glxgears reporting that "vsync is on and the redraw rate should
>> equal the refresh rate" but see 2900 fps reported on a 60 Hz display,
>> with apparently 60 Hz animation. And, in my use case, toolkits that
>> care about timing and do some consistency checks on their swapbuffers
>> execution bail out immediately, telling you to fix your "totally
>> broken graphics driver setup".
>>
>> It's a pure "better than nothing" change for the redirected case,
>> which seems to behave less confusing, at least as no fancy
>> transformations are used, e.g., during desktop transitions.
>>
> OK, fair enough.
>

So, you're ok with that "better than nothing" change?

>> Some consistent crtc selection is another thing that imho would need a
>> bit of work for nouveau and the other drivers. Currently nouveau
>> always selects the 1st crtc for vblank events based swap scheduling
>> and vsync if a window spans multiple displays on xinerama setups,
>> regardless if a non-fullscreen window is displaying on the first or
>> second monitor. Same goes for fullscreen drawables, regardless of how
>> much area is covered by the viewport of a crtc. The other drivers
>> select the crtc to sync by the intersection area of drawable and
>> crtc, so tearing fuer multi-display spanning windows is limited to
>> the "smaller display". It also makes sense to give users some control
>> over this for clone mode, e.g., when they give a presentation and
>> don't care if their laptops flat panel tears, but don't want tearing
>> on the presentation screen for the audience. E.g., one could prefer
>> the --primary output as defined by xrandr.
>>
>>>>   		nv_window_belongs_to_crtc(scrn, draw->x, draw->y,
>>>>   					  draw->width, draw->height);
>>>>   }
>>>> @@ -344,9 +342,40 @@ nouveau_dri2_schedule_swap(ClientPtr client,
>>>> DrawablePtr draw,
>>>>   			   CARD64 *target_msc, CARD64 divisor, CARD64 remainder,
>>>>   			   DRI2SwapEventPtr func, void *data)
>>>>   {
>>>> +	PixmapPtr dst_pix;
>>>> +	PixmapPtr src_pix = nouveau_dri2_buffer(src)->ppix;
>>>>   	struct nouveau_dri2_vblank_state *s;
>>>>   	CARD64 current_msc, expect_msc;
>>>> -	int ret;
>>>> +	int ret, flip = 0;
>>>> +	Bool front_updated;
>>>> +
>>>> +	/* Truncate to match kernel interfaces; means occasional overflow
>>>> +	 * misses, but that's generally not a big deal.
>>>> +	 */
>>>> +	*target_msc&= 0xffffffff;
>>>> +	divisor&= 0xffffffff;
>>>> +	remainder&= 0xffffffff;
>>>> +
>>> This doesn't really fix the problem with our 32bit counters wrapping
>>> around, but, as the comment says, it's not a big deal...
>>>
>>
>> Yes. Another item, get 64-bit counters and api for the kernel
>> drm. Mostly to make explicit that there is a 32-bit limit in place.
>>
>>>> +	/* Update frontbuffer pixmap and name: Could have changed due to
>>>> +	 * window (un)redirection as part of compositing.
>>>> +	 */
>>>> +	front_updated = update_front(draw, dst);
>>>> +
>>>> +	/* Assign frontbuffer pixmap, after update in update_front() */
>>>> +	dst_pix = nouveau_dri2_buffer(dst)->ppix;
>>>> +
>>>> +	/* Flips need to be submitted one frame before */
>>>> +	if (DRI2CanFlip(draw)&&  front_updated&&
>>>> +	    can_exchange(draw, dst_pix, src_pix)) {
>>>> +		flip = 1;
>>>> +	}
>>>> +
>>>> +	/* Correct target_msc by 'flip' if this is a page-flipped swap.
>>>> +	 * Do it early, so handling of different timing constraints
>>>> +	 * for divisor, remainder and msc vs. target_msc works.
>>>> +	 */
>>>> +	if (*target_msc>  0)
>>>> +		*target_msc -= (CARD64) flip;
>>>
>>> We don't need the code above, blits are submitted one frame before as
>>> well - the wait for the final vblank is done in hardware by the GPU
>>> itself, that way we don't have to worry about tearing caused by the
>>> GPU
>>> being too busy to finish all its previous work in time for the
>>> specified
>>> vblank interval.
>>>
>>
>> Oh ok, thanks. I have special measurement equipment here to test
>> pageflipped swaps for timing, but can't test the copyswap case
>> easily. My toolkit was complaining loudly about inconsistencies, so i
>> was just assuming it is due to the same logic as on other gpu's +
>> missing code in the ddx. If copy-swaps are intentionally scheduled
>> one frame ahead, then DRI2SwapComplete timestamps would need to be
>> corrected for that. Currently you get the puzzling result from the
>> timestamps that swaps complete before they were even scheduled by the
>> client, typically a clear indication of broken vsync support in the
>> driver.
>>
> Heh, yeah...
>

I will change the patch to remove the unneccessary bits and try if the 
DRI2SwapComplete timestamps for the copy-swap case can be "fixed" instead.

>> Do you know how this is done at the hardware level? Exactly as with
>> pageflips? The gpu programming seems to be the same in the ddx.
>
> Yes, we use the same synchronization mechanism for pageflips and blits.
>

Hm. Then would it be easily possible for the kms-driver to emit 
"pageflip completion" events for blits as well, e.g., when the drawing 
engine continues or the main x server channel submits the blit? That 
would be a simple and reliable way to timestamp blit-swaps on nouveau as 
well. I've come up with some sketchy ideas to do this on intel and ati, 
but didn't get around to test them so far. Their implementation will be 
quite a bit more involved.

>> Is the blip operation started at leading edge of the vblank interval?
>> Or anywhere inside the vblank interval (level triggered)? Are such
>> blits submitted on a separate fifo (or even dma engine?) in the gpu to
>> avoid stalling the rest of the command stream until vblank?
>
> It depends, right now we have two completely different implementations
> and we use one or the other depending on the card generation:
>
> On nv11-nv4x, we use the PGRAPH vsync methods (0x120-0x134), that means
> it's the drawing engine that waits. Basically you have a counter that's
> incremented by a CRTC of your choice when it reaches a scanline range of
> your choice, wrapping around at a configurable value; you can put the
> drawing engine to sleep until the counter reaches a given value. Right
> now we make it wait until somewhere between vdisplay-3 and vdisplay-1
> before going on with the swap.
>

Interesting, thanks for the explanation. Maybe that counter could also 
be used to implement a hardware vblank counter on pre-NV50? Currently 
the .get_vblank_counter hook is not correctly implemented in the 
nouveau-kms driver. It currently hooks up to drm_vblank_count(), i.e., 
it uses the value of the software drm counter which it is supposed to 
reinitialize from scratch with fresh and independent values from the 
hardware. At the moment this is basically a no-op and the drm will lose 
vblank counts whenever it disables vblank irq's for power saving.

I wanted to prepare a patch for this. For NV-50 there is a hardware 
vblank counter. For earlier cards i couldn't find one, last time i 
searched six month ago?

>  From nv5x on, we use PFIFO semaphores to suspend the execution of the
> channel (right now the main X server channel but this could be changed)
> until a pre-allocated memory location gets a given value, which is
> written there manually by the PDISPLAY vblank interrupt handler. I'm not
> sure when exactly this IRQ happens, most likely it can be configured,
> but I have reasons to believe that in some set-ups it happens at the
> end of the vblank period causing the tearing I've seen a few times.
>

I've observed something similar on my QuadroFX-570 here with pageflips 
as well. The kms-pageflip seems to always happen in scanline 5 of the 
active scanout, instead of inside the vblank. Either that, or there's 
some funny delay due to some additional buffering in the gpu between 
crtc and output port?

Thanks,
-mario

Re: [PATCH 3/3] dri2: Fixes to swap scheduling, especially for copy-swaps.

[Francisco Jerez]

[-- Attachment #1.1.1: Type: text/plain, Size: 5429 bytes --]

Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org> writes:

> On 09/09/2011 11:14 PM, Francisco Jerez wrote:
>> Mario Kleiner<mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org>  writes:
>>
>>>[...]
>>> But the current implementation under a compositor is not great. You
>>> get glxgears reporting that "vsync is on and the redraw rate should
>>> equal the refresh rate" but see 2900 fps reported on a 60 Hz display,
>>> with apparently 60 Hz animation. And, in my use case, toolkits that
>>> care about timing and do some consistency checks on their swapbuffers
>>> execution bail out immediately, telling you to fix your "totally
>>> broken graphics driver setup".
>>>
>>> It's a pure "better than nothing" change for the redirected case,
>>> which seems to behave less confusing, at least as no fancy
>>> transformations are used, e.g., during desktop transitions.
>>>
>> OK, fair enough.
>>
>
> So, you're ok with that "better than nothing" change?
>
Yeah, but it probably deserves its own separate patch.

>>>[...]
>>> Oh ok, thanks. I have special measurement equipment here to test
>>> pageflipped swaps for timing, but can't test the copyswap case
>>> easily. My toolkit was complaining loudly about inconsistencies, so i
>>> was just assuming it is due to the same logic as on other gpu's +
>>> missing code in the ddx. If copy-swaps are intentionally scheduled
>>> one frame ahead, then DRI2SwapComplete timestamps would need to be
>>> corrected for that. Currently you get the puzzling result from the
>>> timestamps that swaps complete before they were even scheduled by the
>>> client, typically a clear indication of broken vsync support in the
>>> driver.
>>>
>> Heh, yeah...
>>
>
> I will change the patch to remove the unneccessary bits and try if the
> DRI2SwapComplete timestamps for the copy-swap case can be "fixed"
> instead.
>
We should probably fix the kernel interface for that, instead of adding
more band-aids to userspace.

>>> Do you know how this is done at the hardware level? Exactly as with
>>> pageflips? The gpu programming seems to be the same in the ddx.
>>
>> Yes, we use the same synchronization mechanism for pageflips and blits.
>>
>
> Hm. Then would it be easily possible for the kms-driver to emit
> "pageflip completion" events for blits as well, e.g., when the drawing
> engine continues or the main x server channel submits the blit? That
> would be a simple and reliable way to timestamp blit-swaps on nouveau
> as well. I've come up with some sketchy ideas to do this on intel and
> ati, but didn't get around to test them so far. Their implementation
> will be quite a bit more involved.
>
Yes, the implementation would be exactly the same as what we use to get
pageflip completion events, we're just missing the interface to expose
it to the user.

>>> Is the blip operation started at leading edge of the vblank interval?
>>> Or anywhere inside the vblank interval (level triggered)? Are such
>>> blits submitted on a separate fifo (or even dma engine?) in the gpu to
>>> avoid stalling the rest of the command stream until vblank?
>>
>> It depends, right now we have two completely different implementations
>> and we use one or the other depending on the card generation:
>>
>> On nv11-nv4x, we use the PGRAPH vsync methods (0x120-0x134), that means
>> it's the drawing engine that waits. Basically you have a counter that's
>> incremented by a CRTC of your choice when it reaches a scanline range of
>> your choice, wrapping around at a configurable value; you can put the
>> drawing engine to sleep until the counter reaches a given value. Right
>> now we make it wait until somewhere between vdisplay-3 and vdisplay-1
>> before going on with the swap.
>>
>
> Interesting, thanks for the explanation. Maybe that counter could also
> be used to implement a hardware vblank counter on pre-NV50? Currently
> the .get_vblank_counter hook is not correctly implemented in the
> nouveau-kms driver. It currently hooks up to drm_vblank_count(), i.e.,
> it uses the value of the software drm counter which it is supposed to
> reinitialize from scratch with fresh and independent values from the
> hardware. At the moment this is basically a no-op and the drm will
> lose vblank counts whenever it disables vblank irq's for power saving.
>
> I wanted to prepare a patch for this. For NV-50 there is a hardware
> vblank counter. For earlier cards i couldn't find one, last time i
> searched six month ago?
>
I'm almost certain that you couldn't because there isn't one...

>>  From nv5x on, we use PFIFO semaphores to suspend the execution of the
>> channel (right now the main X server channel but this could be changed)
>> until a pre-allocated memory location gets a given value, which is
>> written there manually by the PDISPLAY vblank interrupt handler. I'm not
>> sure when exactly this IRQ happens, most likely it can be configured,
>> but I have reasons to believe that in some set-ups it happens at the
>> end of the vblank period causing the tearing I've seen a few times.
>>
>
> I've observed something similar on my QuadroFX-570 here with pageflips
> as well. The kms-pageflip seems to always happen in scanline 5 of the
> active scanout, instead of inside the vblank. Either that, or there's
> some funny delay due to some additional buffering in the gpu between
> crtc and output port?
>
I'd say the former, but I may be wrong.

> Thanks,
> -mario

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Re: [PATCH 3/3] dri2: Fixes to swap scheduling, especially for copy-swaps.

[Francisco Jerez]

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Francisco Jerez <currojerez-sGOZH3hwPm2sTnJN9+BGXg@public.gmane.org> writes:

> Mario Kleiner <mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org> writes:
>
>> On 09/09/2011 11:14 PM, Francisco Jerez wrote:
>>> Mario Kleiner<mario.kleiner-TdbV1Z3I5XE0NhjG498hmQ@public.gmane.org>  writes:
>>>
>>>>[...]
>>>> Is the blip operation started at leading edge of the vblank interval?
>>>> Or anywhere inside the vblank interval (level triggered)? Are such
>>>> blits submitted on a separate fifo (or even dma engine?) in the gpu to
>>>> avoid stalling the rest of the command stream until vblank?
>>>
>>> It depends, right now we have two completely different implementations
>>> and we use one or the other depending on the card generation:
>>>
>>> On nv11-nv4x, we use the PGRAPH vsync methods (0x120-0x134), that means
>>> it's the drawing engine that waits. Basically you have a counter that's
>>> incremented by a CRTC of your choice when it reaches a scanline range of
>>> your choice, wrapping around at a configurable value; you can put the
>>> drawing engine to sleep until the counter reaches a given value. Right
>>> now we make it wait until somewhere between vdisplay-3 and vdisplay-1
>>> before going on with the swap.
>>>
>>
>> Interesting, thanks for the explanation. Maybe that counter could also
>> be used to implement a hardware vblank counter on pre-NV50?

I forgot to answer to this question... Not really, these counters are
(IIRC) only 3 bits wide, and they need PGRAPH intervention to get
incremented, so they're quite useless for anything more sophisticated
than what we're doing right now.

>>[...]

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