Re: [Intel-gfx] [PATCH] drm/i915/gem: Don't try to map and fence 8K/bigjoiner scanout buffers

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Oct 25, 2021 at 11:38:11PM -0700, Vivek Kasireddy wrote:
> On platforms capable of allowing 8K (7680 x 4320) modes, pinning 2 or
> more framebuffers/scanout buffers results in only one that is mappable/
> fenceable. Therefore, pageflipping between these 2 FBs where only one
> is mappable/fenceable creates latencies large enough to miss alternate
> vblanks thereby producing less optimal framerate.
> 
> This mainly happens because when i915_gem_object_pin_to_display_plane()
> is called to pin one of the FB objs, the associated vma is identified
> as misplaced and therefore i915_vma_unbind() is called which unbinds and
> evicts it. This misplaced vma gets subseqently pinned only when
> i915_gem_object_ggtt_pin_ww() is called without the mappable flag. This
> results in a latency of ~10ms and happens every other vblank/repaint cycle.
> 
> Testcase:
> Running Weston and weston-simple-egl on an Alderlake_S (ADLS) platform
> with a 8K@60 mode results in only ~40 FPS. Since upstream Weston submits
> a frame ~7ms before the next vblank, the latencies seen between atomic
> commit and flip event is 7, 24 (7 + 16.66), 7, 24..... suggesting that
> it misses the vblank every other frame.
> 
> Here is the ftrace snippet that shows the source of the ~10ms latency:
>               i915_gem_object_pin_to_display_plane() {
> 0.102 us   |    i915_gem_object_set_cache_level();
>                 i915_gem_object_ggtt_pin_ww() {
> 0.390 us   |      i915_vma_instance();
> 0.178 us   |      i915_vma_misplaced();
>                   i915_vma_unbind() {
>                   __i915_active_wait() {
> 0.082 us   |        i915_active_acquire_if_busy();
> 0.475 us   |      }
>                   intel_runtime_pm_get() {
> 0.087 us   |        intel_runtime_pm_acquire();
> 0.259 us   |      }
>                   __i915_active_wait() {
> 0.085 us   |        i915_active_acquire_if_busy();
> 0.240 us   |      }
>                   __i915_vma_evict() {
>                     ggtt_unbind_vma() {
>                       gen8_ggtt_clear_range() {
> 10507.255 us |        }
> 10507.689 us |      }
> 10508.516 us |   }
> 
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
> Cc: Manasi Navare <manasi.d.navare@intel.com>
> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_fb_pin.c  | 11 +++++++++--
>  drivers/gpu/drm/i915/display/intel_overlay.c | 11 ++++++++---
>  drivers/gpu/drm/i915/gem/i915_gem_domain.c   |  6 ++++--
>  drivers/gpu/drm/i915/gem/i915_gem_object.h   |  3 ++-
>  4 files changed, 23 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_fb_pin.c b/drivers/gpu/drm/i915/display/intel_fb_pin.c
> index 3f77f3013584..53c156d9a9f9 100644
> --- a/drivers/gpu/drm/i915/display/intel_fb_pin.c
> +++ b/drivers/gpu/drm/i915/display/intel_fb_pin.c
> @@ -144,7 +144,7 @@ intel_pin_and_fence_fb_obj(struct drm_framebuffer *fb,
>  
>  	if (!ret) {
>  		vma = i915_gem_object_pin_to_display_plane(obj, &ww, alignment,
> -							   view, pinctl);
> +							   view, pinctl, uses_fence);
>  		if (IS_ERR(vma)) {
>  			ret = PTR_ERR(vma);
>  			goto err_unpin;
> @@ -218,9 +218,16 @@ int intel_plane_pin_fb(struct intel_plane_state *plane_state)
>  		INTEL_INFO(dev_priv)->display.cursor_needs_physical;
>  
>  	if (!intel_fb_uses_dpt(fb)) {
> +		struct intel_crtc *crtc = to_intel_crtc(plane_state->hw.crtc);
> +		struct intel_crtc_state *crtc_state =
> +					to_intel_crtc_state(crtc->base.state);
> +		bool uses_fence = intel_plane_uses_fence(plane_state);
> +		bool is_bigjoiner = crtc_state->bigjoiner ||
> +				    crtc_state->bigjoiner_slave;

Bigjoiner is just an implementation detail. It is not the cause of any
of this.

> +
>  		vma = intel_pin_and_fence_fb_obj(fb, phys_cursor,
>  						 &plane_state->view.gtt,
> -						 intel_plane_uses_fence(plane_state),
> +						 uses_fence && !is_bigjoiner,
>  						 &plane_state->flags);
>  		if (IS_ERR(vma))
>  			return PTR_ERR(vma);
> diff --git a/drivers/gpu/drm/i915/display/intel_overlay.c b/drivers/gpu/drm/i915/display/intel_overlay.c
> index 7e3f5c6ca484..e9563b40b911 100644
> --- a/drivers/gpu/drm/i915/display/intel_overlay.c
> +++ b/drivers/gpu/drm/i915/display/intel_overlay.c
> @@ -755,10 +755,14 @@ static u32 overlay_cmd_reg(struct drm_intel_overlay_put_image *params)
>  	return cmd;
>  }
>  
> -static struct i915_vma *intel_overlay_pin_fb(struct drm_i915_gem_object *new_bo)
> +static struct i915_vma *intel_overlay_pin_fb(struct drm_i915_gem_object *new_bo,
> +					     struct intel_overlay *overlay)
>  {
>  	struct i915_gem_ww_ctx ww;
>  	struct i915_vma *vma;
> +	const struct intel_plane_state *plane_state =
> +		to_intel_plane_state(overlay->crtc->base.primary->state);
> +	bool uses_fence = intel_plane_uses_fence(plane_state);
>  	int ret;
>  
>  	i915_gem_ww_ctx_init(&ww, true);
> @@ -766,7 +770,8 @@ static struct i915_vma *intel_overlay_pin_fb(struct drm_i915_gem_object *new_bo)
>  	ret = i915_gem_object_lock(new_bo, &ww);
>  	if (!ret) {
>  		vma = i915_gem_object_pin_to_display_plane(new_bo, &ww, 0,
> -							   NULL, PIN_MAPPABLE);
> +							   NULL, PIN_MAPPABLE,
> +							   uses_fence);
>  		ret = PTR_ERR_OR_ZERO(vma);
>  	}
>  	if (ret == -EDEADLK) {
> @@ -802,7 +807,7 @@ static int intel_overlay_do_put_image(struct intel_overlay *overlay,
>  
>  	atomic_inc(&dev_priv->gpu_error.pending_fb_pin);
>  
> -	vma = intel_overlay_pin_fb(new_bo);
> +	vma = intel_overlay_pin_fb(new_bo, overlay);
>  	if (IS_ERR(vma)) {
>  		ret = PTR_ERR(vma);
>  		goto out_pin_section;
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_domain.c b/drivers/gpu/drm/i915/gem/i915_gem_domain.c
> index b684a62bf3b0..b9108f13cc49 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_domain.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_domain.c
> @@ -375,7 +375,8 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj,
>  				     struct i915_gem_ww_ctx *ww,
>  				     u32 alignment,
>  				     const struct i915_ggtt_view *view,
> -				     unsigned int flags)
> +				     unsigned int flags,
> +				     bool uses_fence)
>  {
>  	struct drm_i915_private *i915 = to_i915(obj->base.dev);
>  	struct i915_vma *vma;
> @@ -411,7 +412,8 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj,
>  	 */
>  	vma = ERR_PTR(-ENOSPC);
>  	if ((flags & PIN_MAPPABLE) == 0 &&
> -	    (!view || view->type == I915_GGTT_VIEW_NORMAL))
> +	    (!view || view->type == I915_GGTT_VIEW_NORMAL) &&
> +	    uses_fence)
>  		vma = i915_gem_object_ggtt_pin_ww(obj, ww, view, 0, alignment,
>  						  flags | PIN_MAPPABLE |
>  						  PIN_NONBLOCK);
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> index a5479ac7a4ad..e83564fa57ca 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> @@ -534,7 +534,8 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj,
>  				     struct i915_gem_ww_ctx *ww,
>  				     u32 alignment,
>  				     const struct i915_ggtt_view *view,
> -				     unsigned int flags);
> +				     unsigned int flags,
> +				     bool uses_fence);
>  
>  void i915_gem_object_make_unshrinkable(struct drm_i915_gem_object *obj);
>  void i915_gem_object_make_shrinkable(struct drm_i915_gem_object *obj);
> -- 
> 2.31.1

-- 
Ville Syrjälä
Intel