Re: [PATCH 31/43] drm/i915/bdw: Handle context switch events

Daniel Vetter
2014-08-14T20:17:30Z

On Thu, Jul 24, 2014 at 05:04:39PM +0100, Thomas Daniel wrote:
> Handle all context status events in the context status buffer on every
> context switch interrupt. We only remove work from the execlist queue
> after a context status buffer reports that it has completed and we only
> attempt to schedule new contexts on interrupt when a previously submitted
> context completes (unless no contexts are queued, which means the GPU is
> free).
>
> We canot call intel_runtime_pm_get() in an interrupt (or with a spinlock
> grabbed, FWIW), because it might sleep, which is not a nice thing to do.
> Instead, do the runtime_pm get/put together with the create/destroy request,
> and handle the forcewake get/put directly.
>
> Signed-off-by: Thomas Daniel <thomas.daniel@intel.com>
>
> v2: Unreferencing the context when we are freeing the request might free
> the backing bo, which requires the struct_mutex to be grabbed, so defer
> unreferencing and freeing to a bottom half.
>
> v3:
> - Ack the interrupt inmediately, before trying to handle it (fix for
> missing interrupts by Bob Beckett <robert.beckett@intel.com>).
> - Update the Context Status Buffer Read Pointer, just in case (spotted
> by Damien Lespiau).
>
> v4: New namespace and multiple rebase changes.
>
> v5: Squash with "drm/i915/bdw: Do not call intel_runtime_pm_get() in an
> interrupt", as suggested by Daniel.
>
> Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
> ---
> drivers/gpu/drm/i915/i915_irq.c | 35 ++++++---
> drivers/gpu/drm/i915/intel_lrc.c | 129 +++++++++++++++++++++++++++++--
> drivers/gpu/drm/i915/intel_lrc.h | 3 +
> drivers/gpu/drm/i915/intel_ringbuffer.h | 1 +
> 4 files changed, 151 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index f77a4ca..e4077d1 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -1628,6 +1628,7 @@ static irqreturn_t gen8_gt_irq_handler(struct drm_device *dev,
> struct drm_i915_private *dev_priv,
> u32 master_ctl)
> {
> + struct intel_engine_cs *ring;
> u32 rcs, bcs, vcs;
> uint32_t tmp = 0;
> irqreturn_t ret = IRQ_NONE;
> @@ -1637,14 +1638,20 @@ static irqreturn_t gen8_gt_irq_handler(struct drm_device *dev,
> if (tmp) {
> I915_WRITE(GEN8_GT_IIR(0), tmp);
> ret = IRQ_HANDLED;
> +
> rcs = tmp >> GEN8_RCS_IRQ_SHIFT;
> - bcs = tmp >> GEN8_BCS_IRQ_SHIFT;
> + ring = &dev_priv->ring[RCS];
> if (rcs & GT_RENDER_USER_INTERRUPT)
> - notify_ring(dev, &dev_priv->ring[RCS]);
> + notify_ring(dev, ring);
> + if (rcs & GEN8_GT_CONTEXT_SWITCH_INTERRUPT)
> + intel_execlists_handle_ctx_events(ring);
> +
> + bcs = tmp >> GEN8_BCS_IRQ_SHIFT;
> + ring = &dev_priv->ring[BCS];
> if (bcs & GT_RENDER_USER_INTERRUPT)
> - notify_ring(dev, &dev_priv->ring[BCS]);
> - if ((rcs | bcs) & GEN8_GT_CONTEXT_SWITCH_INTERRUPT)
> - DRM_DEBUG_DRIVER("TODO: Context switch\n");
> + notify_ring(dev, ring);
> + if (bcs & GEN8_GT_CONTEXT_SWITCH_INTERRUPT)
> + intel_execlists_handle_ctx_events(ring);

Also patch split fail here, the above two cases should have been in an
earlier patch that added the basic irq handling.
-Daniel

> } else
> DRM_ERROR("The master control interrupt lied (GT0)!\n");
> }
> @@ -1654,16 +1661,20 @@ static irqreturn_t gen8_gt_irq_handler(struct drm_device *dev,
> if (tmp) {
> I915_WRITE(GEN8_GT_IIR(1), tmp);
> ret = IRQ_HANDLED;
> +
> vcs = tmp >> GEN8_VCS1_IRQ_SHIFT;
> + ring = &dev_priv->ring[VCS];
> if (vcs & GT_RENDER_USER_INTERRUPT)
> - notify_ring(dev, &dev_priv->ring[VCS]);
> + notify_ring(dev, ring);
> if (vcs & GEN8_GT_CONTEXT_SWITCH_INTERRUPT)
> - DRM_DEBUG_DRIVER("TODO: Context switch\n");
> + intel_execlists_handle_ctx_events(ring);
> +
> vcs = tmp >> GEN8_VCS2_IRQ_SHIFT;
> + ring = &dev_priv->ring[VCS2];
> if (vcs & GT_RENDER_USER_INTERRUPT)
> - notify_ring(dev, &dev_priv->ring[VCS2]);
> + notify_ring(dev, ring);
> if (vcs & GEN8_GT_CONTEXT_SWITCH_INTERRUPT)
> - DRM_DEBUG_DRIVER("TODO: Context switch\n");
> + intel_execlists_handle_ctx_events(ring);
> } else
> DRM_ERROR("The master control interrupt lied (GT1)!\n");
> }
> @@ -1684,11 +1695,13 @@ static irqreturn_t gen8_gt_irq_handler(struct drm_device *dev,
> if (tmp) {
> I915_WRITE(GEN8_GT_IIR(3), tmp);
> ret = IRQ_HANDLED;
> +
> vcs = tmp >> GEN8_VECS_IRQ_SHIFT;
> + ring = &dev_priv->ring[VECS];
> if (vcs & GT_RENDER_USER_INTERRUPT)
> - notify_ring(dev, &dev_priv->ring[VECS]);
> + notify_ring(dev, ring);
> if (vcs & GEN8_GT_CONTEXT_SWITCH_INTERRUPT)
> - DRM_DEBUG_DRIVER("TODO: Context switch\n");
> + intel_execlists_handle_ctx_events(ring);
> } else
> DRM_ERROR("The master control interrupt lied (GT3)!\n");
> }
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 9e91169..65f4f26 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -49,6 +49,22 @@
> #define RING_ELSP(ring) ((ring)->mmio_base+0x230)
> #define RING_EXECLIST_STATUS(ring) ((ring)->mmio_base+0x234)
> #define RING_CONTEXT_CONTROL(ring) ((ring)->mmio_base+0x244)
> +#define RING_CONTEXT_STATUS_BUF(ring) ((ring)->mmio_base+0x370)
> +#define RING_CONTEXT_STATUS_PTR(ring) ((ring)->mmio_base+0x3a0)
> +
> +#define RING_EXECLIST_QFULL (1 << 0x2)
> +#define RING_EXECLIST1_VALID (1 << 0x3)
> +#define RING_EXECLIST0_VALID (1 << 0x4)
> +#define RING_EXECLIST_ACTIVE_STATUS (3 << 0xE)
> +#define RING_EXECLIST1_ACTIVE (1 << 0x11)
> +#define RING_EXECLIST0_ACTIVE (1 << 0x12)
> +
> +#define GEN8_CTX_STATUS_IDLE_ACTIVE (1 << 0)
> +#define GEN8_CTX_STATUS_PREEMPTED (1 << 1)
> +#define GEN8_CTX_STATUS_ELEMENT_SWITCH (1 << 2)
> +#define GEN8_CTX_STATUS_ACTIVE_IDLE (1 << 3)
> +#define GEN8_CTX_STATUS_COMPLETE (1 << 4)
> +#define GEN8_CTX_STATUS_LITE_RESTORE (1 << 15)
>
> #define CTX_LRI_HEADER_0 0x01
> #define CTX_CONTEXT_CONTROL 0x02
> @@ -147,6 +163,7 @@ static void execlists_elsp_write(struct intel_engine_cs *ring,
> struct drm_i915_private *dev_priv = ring->dev->dev_private;
> uint64_t temp = 0;
> uint32_t desc[4];
> + unsigned long flags;
>
> /* XXX: You must always write both descriptors in the order below. */
> if (ctx_obj1)
> @@ -160,9 +177,17 @@ static void execlists_elsp_write(struct intel_engine_cs *ring,
> desc[3] = (u32)(temp >> 32);
> desc[2] = (u32)temp;
>
> - /* Set Force Wakeup bit to prevent GT from entering C6 while
> - * ELSP writes are in progress */
> - gen6_gt_force_wake_get(dev_priv, FORCEWAKE_ALL);
> + /* Set Force Wakeup bit to prevent GT from entering C6 while ELSP writes
> + * are in progress.
> + *
> + * The other problem is that we can't just call gen6_gt_force_wake_get()
> + * because that function calls intel_runtime_pm_get(), which might sleep.
> + * Instead, we do the runtime_pm_get/put when creating/destroying requests.
> + */
> + spin_lock_irqsave(&dev_priv->uncore.lock, flags);
> + if (dev_priv->uncore.forcewake_count++ == 0)
> + dev_priv->uncore.funcs.force_wake_get(dev_priv, FORCEWAKE_ALL);
> + spin_unlock_irqrestore(&dev_priv->uncore.lock, flags);
>
> I915_WRITE(RING_ELSP(ring), desc[1]);
> I915_WRITE(RING_ELSP(ring), desc[0]);
> @@ -173,7 +198,11 @@ static void execlists_elsp_write(struct intel_engine_cs *ring,
> /* ELSP is a wo register, so use another nearby reg for posting instead */
> POSTING_READ(RING_EXECLIST_STATUS(ring));
>
> - gen6_gt_force_wake_put(dev_priv, FORCEWAKE_ALL);
> + /* Release Force Wakeup (see the big comment above). */
> + spin_lock_irqsave(&dev_priv->uncore.lock, flags);
> + if (--dev_priv->uncore.forcewake_count == 0)
> + dev_priv->uncore.funcs.force_wake_put(dev_priv, FORCEWAKE_ALL);
> + spin_unlock_irqrestore(&dev_priv->uncore.lock, flags);
> }
>
> static int execlists_ctx_write_tail(struct drm_i915_gem_object *ctx_obj, u32 tail)
> @@ -221,6 +250,9 @@ static void execlists_context_unqueue(struct intel_engine_cs *ring)
> {
> struct intel_ctx_submit_request *req0 = NULL, *req1 = NULL;
> struct intel_ctx_submit_request *cursor = NULL, *tmp = NULL;
> + struct drm_i915_private *dev_priv = ring->dev->dev_private;
> +
> + assert_spin_locked(&ring->execlist_lock);
>
> if (list_empty(&ring->execlist_queue))
> return;
> @@ -233,8 +265,7 @@ static void execlists_context_unqueue(struct intel_engine_cs *ring)
> /* Same ctx: ignore first request, as second request
> * will update tail past first request's workload */
> list_del(&req0->execlist_link);
> - i915_gem_context_unreference(req0->ctx);
> - kfree(req0);
> + queue_work(dev_priv->wq, &req0->work);
> req0 = cursor;
> } else {
> req1 = cursor;
> @@ -246,6 +277,89 @@ static void execlists_context_unqueue(struct intel_engine_cs *ring)
> req1? req1->ctx : NULL, req1? req1->tail : 0));
> }
>
> +static bool execlists_check_remove_request(struct intel_engine_cs *ring,
> + u32 request_id)
> +{
> + struct drm_i915_private *dev_priv = ring->dev->dev_private;
> + struct intel_ctx_submit_request *head_req;
> +
> + assert_spin_locked(&ring->execlist_lock);
> +
> + head_req = list_first_entry_or_null(&ring->execlist_queue,
> + struct intel_ctx_submit_request, execlist_link);
> + if (head_req != NULL) {
> + struct drm_i915_gem_object *ctx_obj =
> + head_req->ctx->engine[ring->id].state;
> + if (intel_execlists_ctx_id(ctx_obj) == request_id) {
> + list_del(&head_req->execlist_link);
> + queue_work(dev_priv->wq, &head_req->work);
> + return true;
> + }
> + }
> +
> + return false;
> +}
> +
> +void intel_execlists_handle_ctx_events(struct intel_engine_cs *ring)
> +{
> + struct drm_i915_private *dev_priv = ring->dev->dev_private;
> + u32 status_pointer;
> + u8 read_pointer;
> + u8 write_pointer;
> + u32 status;
> + u32 status_id;
> + u32 submit_contexts = 0;
> +
> + status_pointer = I915_READ(RING_CONTEXT_STATUS_PTR(ring));
> +
> + read_pointer = ring->next_context_status_buffer;
> + write_pointer = status_pointer & 0x07;
> + if (read_pointer > write_pointer)
> + write_pointer += 6;
> +
> + spin_lock(&ring->execlist_lock);
> +
> + while (read_pointer < write_pointer) {
> + read_pointer++;
> + status = I915_READ(RING_CONTEXT_STATUS_BUF(ring) +
> + (read_pointer % 6) * 8);
> + status_id = I915_READ(RING_CONTEXT_STATUS_BUF(ring) +
> + (read_pointer % 6) * 8 + 4);
> +
> + if (status & GEN8_CTX_STATUS_COMPLETE) {
> + if (execlists_check_remove_request(ring, status_id))
> + submit_contexts++;
> + }
> + }
> +
> + if (submit_contexts != 0)
> + execlists_context_unqueue(ring);
> +
> + spin_unlock(&ring->execlist_lock);
> +
> + WARN(submit_contexts > 2, "More than two context complete events?\n");
> + ring->next_context_status_buffer = write_pointer % 6;
> +
> + I915_WRITE(RING_CONTEXT_STATUS_PTR(ring),
> + ((u32)ring->next_context_status_buffer & 0x07) << 8);
> +}
> +
> +static void execlists_free_request_task(struct work_struct *work)
> +{
> + struct intel_ctx_submit_request *req =
> + container_of(work, struct intel_ctx_submit_request, work);
> + struct drm_device *dev = req->ring->dev;
> + struct drm_i915_private *dev_priv = dev->dev_private;
> +
> + intel_runtime_pm_put(dev_priv);
> +
> + mutex_lock(&dev->struct_mutex);
> + i915_gem_context_unreference(req->ctx);
> + mutex_unlock(&dev->struct_mutex);
> +
> + kfree(req);
> +}
> +
> static int execlists_context_queue(struct intel_engine_cs *ring,
> struct intel_context *to,
> u32 tail)
> @@ -261,6 +375,8 @@ static int execlists_context_queue(struct intel_engine_cs *ring,
> i915_gem_context_reference(req->ctx);
> req->ring = ring;
> req->tail = tail;
> + INIT_WORK(&req->work, execlists_free_request_task);
> + intel_runtime_pm_get(dev_priv);
>
> spin_lock_irqsave(&ring->execlist_lock, flags);
>
> @@ -908,6 +1024,7 @@ static int logical_ring_init(struct drm_device *dev, struct intel_engine_cs *rin
>
> INIT_LIST_HEAD(&ring->execlist_queue);
> spin_lock_init(&ring->execlist_lock);
> + ring->next_context_status_buffer = 0;
>
> ret = intel_lr_context_deferred_create(dctx, ring);
> if (ret)
> diff --git a/drivers/gpu/drm/i915/intel_lrc.h b/drivers/gpu/drm/i915/intel_lrc.h
> index 14492a9..2e8929f 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.h
> +++ b/drivers/gpu/drm/i915/intel_lrc.h
> @@ -66,6 +66,9 @@ struct intel_ctx_submit_request {
> u32 tail;
>
> struct list_head execlist_link;
> + struct work_struct work;
> };
>
> +void intel_execlists_handle_ctx_events(struct intel_engine_cs *ring);
> +
> #endif /* _INTEL_LRC_H_ */
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
> index 6358823..905d1ba 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> @@ -225,6 +225,7 @@ struct intel_engine_cs {
> /* Execlists */
> spinlock_t execlist_lock;
> struct list_head execlist_queue;
> + u8 next_context_status_buffer;
> u32 irq_keep_mask; /* bitmask for interrupts that should not be masked */
> int (*emit_request)(struct intel_ringbuffer *ringbuf);
> int (*emit_flush)(struct intel_ringbuffer *ringbuf,
> --
> 1.7.9.5
>
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch