Re: [PATCH] drm/i915/gt: Remove direct invocation of breadcrumb signaling

[Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>]

On 02/12/2019 11:08, Chris Wilson wrote:
> Only signal the breadcrumbs from inside the irq_work, simplifying our
> interface and calling conventions.

Making Icelake signaling latency look better? :) A few more words about 
motivation would be good.

Regards,

Tvrtko

> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> ---
>   drivers/gpu/drm/i915/gt/intel_breadcrumbs.c   | 27 +++++++------------
>   drivers/gpu/drm/i915/gt/intel_engine.h        |  4 +--
>   drivers/gpu/drm/i915/gt/intel_gt_irq.c        | 12 ++++-----
>   drivers/gpu/drm/i915/gt/intel_lrc.c           |  2 +-
>   drivers/gpu/drm/i915/gt/intel_reset.c         |  4 +--
>   .../gpu/drm/i915/gt/intel_ring_submission.c   |  2 +-
>   drivers/gpu/drm/i915/gt/intel_rps.c           |  2 +-
>   drivers/gpu/drm/i915/gt/mock_engine.c         |  2 +-
>   drivers/gpu/drm/i915/i915_irq.c               |  8 +++---
>   drivers/gpu/drm/i915/i915_request.c           |  2 +-
>   10 files changed, 27 insertions(+), 38 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
> index 55317081d48b..6acf8208ba79 100644
> --- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
> +++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
> @@ -127,16 +127,15 @@ __dma_fence_signal__notify(struct dma_fence *fence,
>   	}
>   }
>   
> -void intel_engine_breadcrumbs_irq(struct intel_engine_cs *engine)
> +static void signal_irq_work(struct irq_work *work)
>   {
> -	struct intel_breadcrumbs *b = &engine->breadcrumbs;
> +	struct intel_breadcrumbs *b = container_of(work, typeof(*b), irq_work);
>   	const ktime_t timestamp = ktime_get();
>   	struct intel_context *ce, *cn;
>   	struct list_head *pos, *next;
> -	unsigned long flags;
>   	LIST_HEAD(signal);
>   
> -	spin_lock_irqsave(&b->irq_lock, flags);
> +	spin_lock(&b->irq_lock);
>   
>   	if (b->irq_armed && list_empty(&b->signalers))
>   		__intel_breadcrumbs_disarm_irq(b);
> @@ -182,31 +181,23 @@ void intel_engine_breadcrumbs_irq(struct intel_engine_cs *engine)
>   		}
>   	}
>   
> -	spin_unlock_irqrestore(&b->irq_lock, flags);
> +	spin_unlock(&b->irq_lock);
>   
>   	list_for_each_safe(pos, next, &signal) {
>   		struct i915_request *rq =
>   			list_entry(pos, typeof(*rq), signal_link);
>   		struct list_head cb_list;
>   
> -		spin_lock_irqsave(&rq->lock, flags);
> +		spin_lock(&rq->lock);
>   		list_replace(&rq->fence.cb_list, &cb_list);
>   		__dma_fence_signal__timestamp(&rq->fence, timestamp);
>   		__dma_fence_signal__notify(&rq->fence, &cb_list);
> -		spin_unlock_irqrestore(&rq->lock, flags);
> +		spin_unlock(&rq->lock);
>   
>   		i915_request_put(rq);
>   	}
>   }
>   
> -static void signal_irq_work(struct irq_work *work)
> -{
> -	struct intel_engine_cs *engine =
> -		container_of(work, typeof(*engine), breadcrumbs.irq_work);
> -
> -	intel_engine_breadcrumbs_irq(engine);
> -}
> -
>   static void __intel_breadcrumbs_arm_irq(struct intel_breadcrumbs *b)
>   {
>   	struct intel_engine_cs *engine =
> @@ -281,9 +272,9 @@ bool i915_request_enable_breadcrumb(struct i915_request *rq)
>   
>   		/*
>   		 * We keep the seqno in retirement order, so we can break
> -		 * inside intel_engine_breadcrumbs_irq as soon as we've passed
> -		 * the last completed request (or seen a request that hasn't
> -		 * event started). We could iterate the timeline->requests list,
> +		 * inside intel_engine_signal_breadcrumbs as soon as we've
> +		 * passed the last completed request (or seen a request that
> +		 * hasn't event started). We could walk the timeline->requests,
>   		 * but keeping a separate signalers_list has the advantage of
>   		 * hopefully being much smaller than the full list and so
>   		 * provides faster iteration and detection when there are no
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine.h b/drivers/gpu/drm/i915/gt/intel_engine.h
> index 01765a7ec18f..e1750d083c90 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine.h
> +++ b/drivers/gpu/drm/i915/gt/intel_engine.h
> @@ -206,13 +206,11 @@ void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine);
>   void intel_engine_disarm_breadcrumbs(struct intel_engine_cs *engine);
>   
>   static inline void
> -intel_engine_queue_breadcrumbs(struct intel_engine_cs *engine)
> +intel_engine_signal_breadcrumbs(struct intel_engine_cs *engine)
>   {
>   	irq_work_queue(&engine->breadcrumbs.irq_work);
>   }
>   
> -void intel_engine_breadcrumbs_irq(struct intel_engine_cs *engine);
> -
>   void intel_engine_reset_breadcrumbs(struct intel_engine_cs *engine);
>   void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine);
>   
> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_irq.c b/drivers/gpu/drm/i915/gt/intel_gt_irq.c
> index 332b12a574fb..f796bdf1ed30 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gt_irq.c
> +++ b/drivers/gpu/drm/i915/gt/intel_gt_irq.c
> @@ -28,7 +28,7 @@ cs_irq_handler(struct intel_engine_cs *engine, u32 iir)
>   		tasklet = true;
>   
>   	if (iir & GT_RENDER_USER_INTERRUPT) {
> -		intel_engine_queue_breadcrumbs(engine);
> +		intel_engine_signal_breadcrumbs(engine);
>   		tasklet |= intel_engine_needs_breadcrumb_tasklet(engine);
>   	}
>   
> @@ -245,9 +245,9 @@ void gen11_gt_irq_postinstall(struct intel_gt *gt)
>   void gen5_gt_irq_handler(struct intel_gt *gt, u32 gt_iir)
>   {
>   	if (gt_iir & GT_RENDER_USER_INTERRUPT)
> -		intel_engine_breadcrumbs_irq(gt->engine_class[RENDER_CLASS][0]);
> +		intel_engine_signal_breadcrumbs(gt->engine_class[RENDER_CLASS][0]);
>   	if (gt_iir & ILK_BSD_USER_INTERRUPT)
> -		intel_engine_breadcrumbs_irq(gt->engine_class[VIDEO_DECODE_CLASS][0]);
> +		intel_engine_signal_breadcrumbs(gt->engine_class[VIDEO_DECODE_CLASS][0]);
>   }
>   
>   static void gen7_parity_error_irq_handler(struct intel_gt *gt, u32 iir)
> @@ -271,11 +271,11 @@ static void gen7_parity_error_irq_handler(struct intel_gt *gt, u32 iir)
>   void gen6_gt_irq_handler(struct intel_gt *gt, u32 gt_iir)
>   {
>   	if (gt_iir & GT_RENDER_USER_INTERRUPT)
> -		intel_engine_breadcrumbs_irq(gt->engine_class[RENDER_CLASS][0]);
> +		intel_engine_signal_breadcrumbs(gt->engine_class[RENDER_CLASS][0]);
>   	if (gt_iir & GT_BSD_USER_INTERRUPT)
> -		intel_engine_breadcrumbs_irq(gt->engine_class[VIDEO_DECODE_CLASS][0]);
> +		intel_engine_signal_breadcrumbs(gt->engine_class[VIDEO_DECODE_CLASS][0]);
>   	if (gt_iir & GT_BLT_USER_INTERRUPT)
> -		intel_engine_breadcrumbs_irq(gt->engine_class[COPY_ENGINE_CLASS][0]);
> +		intel_engine_signal_breadcrumbs(gt->engine_class[COPY_ENGINE_CLASS][0]);
>   
>   	if (gt_iir & (GT_BLT_CS_ERROR_INTERRUPT |
>   		      GT_BSD_CS_ERROR_INTERRUPT |
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index fef4b7e823f5..ab6f2171e7ac 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -1475,7 +1475,7 @@ static void virtual_xfer_breadcrumbs(struct virtual_engine *ve,
>   	if (!list_empty(&ve->context.signal_link)) {
>   		list_move_tail(&ve->context.signal_link,
>   			       &engine->breadcrumbs.signalers);
> -		intel_engine_queue_breadcrumbs(engine);
> +		intel_engine_signal_breadcrumbs(engine);
>   	}
>   	spin_unlock(&old->breadcrumbs.irq_lock);
>   }
> diff --git a/drivers/gpu/drm/i915/gt/intel_reset.c b/drivers/gpu/drm/i915/gt/intel_reset.c
> index 36189238e13c..7d65aaf7f814 100644
> --- a/drivers/gpu/drm/i915/gt/intel_reset.c
> +++ b/drivers/gpu/drm/i915/gt/intel_reset.c
> @@ -736,7 +736,7 @@ static void reset_finish_engine(struct intel_engine_cs *engine)
>   	engine->reset.finish(engine);
>   	intel_uncore_forcewake_put(engine->uncore, FORCEWAKE_ALL);
>   
> -	intel_engine_breadcrumbs_irq(engine);
> +	intel_engine_signal_breadcrumbs(engine);
>   }
>   
>   static void reset_finish(struct intel_gt *gt, intel_engine_mask_t awake)
> @@ -765,7 +765,7 @@ static void nop_submit_request(struct i915_request *request)
>   	i915_request_mark_complete(request);
>   	spin_unlock_irqrestore(&engine->active.lock, flags);
>   
> -	intel_engine_queue_breadcrumbs(engine);
> +	intel_engine_signal_breadcrumbs(engine);
>   }
>   
>   static void __intel_gt_set_wedged(struct intel_gt *gt)
> diff --git a/drivers/gpu/drm/i915/gt/intel_ring_submission.c b/drivers/gpu/drm/i915/gt/intel_ring_submission.c
> index dcdeef0a776f..0c189807fe36 100644
> --- a/drivers/gpu/drm/i915/gt/intel_ring_submission.c
> +++ b/drivers/gpu/drm/i915/gt/intel_ring_submission.c
> @@ -722,7 +722,7 @@ static int xcs_resume(struct intel_engine_cs *engine)
>   	}
>   
>   	/* Papering over lost _interrupts_ immediately following the restart */
> -	intel_engine_queue_breadcrumbs(engine);
> +	intel_engine_signal_breadcrumbs(engine);
>   out:
>   	intel_uncore_forcewake_put(engine->uncore, FORCEWAKE_ALL);
>   
> diff --git a/drivers/gpu/drm/i915/gt/intel_rps.c b/drivers/gpu/drm/i915/gt/intel_rps.c
> index 08a38a3b90b0..836bbc296158 100644
> --- a/drivers/gpu/drm/i915/gt/intel_rps.c
> +++ b/drivers/gpu/drm/i915/gt/intel_rps.c
> @@ -1566,7 +1566,7 @@ void gen6_rps_irq_handler(struct intel_rps *rps, u32 pm_iir)
>   		return;
>   
>   	if (pm_iir & PM_VEBOX_USER_INTERRUPT)
> -		intel_engine_breadcrumbs_irq(gt->engine[VECS0]);
> +		intel_engine_signal_breadcrumbs(gt->engine[VECS0]);
>   
>   	if (pm_iir & PM_VEBOX_CS_ERROR_INTERRUPT)
>   		DRM_DEBUG("Command parser error, pm_iir 0x%08x\n", pm_iir);
> diff --git a/drivers/gpu/drm/i915/gt/mock_engine.c b/drivers/gpu/drm/i915/gt/mock_engine.c
> index 83f549d203a0..39df9d49a134 100644
> --- a/drivers/gpu/drm/i915/gt/mock_engine.c
> +++ b/drivers/gpu/drm/i915/gt/mock_engine.c
> @@ -77,7 +77,7 @@ static void advance(struct i915_request *request)
>   	i915_request_mark_complete(request);
>   	GEM_BUG_ON(!i915_request_completed(request));
>   
> -	intel_engine_queue_breadcrumbs(request->engine);
> +	intel_engine_signal_breadcrumbs(request->engine);
>   }
>   
>   static void hw_delay_complete(struct timer_list *t)
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 8b338744eddf..88689ff50d61 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -3601,7 +3601,7 @@ static irqreturn_t i8xx_irq_handler(int irq, void *arg)
>   		intel_uncore_write16(&dev_priv->uncore, GEN2_IIR, iir);
>   
>   		if (iir & I915_USER_INTERRUPT)
> -			intel_engine_breadcrumbs_irq(dev_priv->engine[RCS0]);
> +			intel_engine_signal_breadcrumbs(dev_priv->engine[RCS0]);
>   
>   		if (iir & I915_MASTER_ERROR_INTERRUPT)
>   			i8xx_error_irq_handler(dev_priv, eir, eir_stuck);
> @@ -3706,7 +3706,7 @@ static irqreturn_t i915_irq_handler(int irq, void *arg)
>   		I915_WRITE(GEN2_IIR, iir);
>   
>   		if (iir & I915_USER_INTERRUPT)
> -			intel_engine_breadcrumbs_irq(dev_priv->engine[RCS0]);
> +			intel_engine_signal_breadcrumbs(dev_priv->engine[RCS0]);
>   
>   		if (iir & I915_MASTER_ERROR_INTERRUPT)
>   			i9xx_error_irq_handler(dev_priv, eir, eir_stuck);
> @@ -3848,10 +3848,10 @@ static irqreturn_t i965_irq_handler(int irq, void *arg)
>   		I915_WRITE(GEN2_IIR, iir);
>   
>   		if (iir & I915_USER_INTERRUPT)
> -			intel_engine_breadcrumbs_irq(dev_priv->engine[RCS0]);
> +			intel_engine_signal_breadcrumbs(dev_priv->engine[RCS0]);
>   
>   		if (iir & I915_BSD_USER_INTERRUPT)
> -			intel_engine_breadcrumbs_irq(dev_priv->engine[VCS0]);
> +			intel_engine_signal_breadcrumbs(dev_priv->engine[VCS0]);
>   
>   		if (iir & I915_MASTER_ERROR_INTERRUPT)
>   			i9xx_error_irq_handler(dev_priv, eir, eir_stuck);
> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> index a558f64186fa..3109b8a79b9f 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -415,7 +415,7 @@ bool __i915_request_submit(struct i915_request *request)
>   	if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &request->fence.flags) &&
>   	    !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &request->fence.flags) &&
>   	    !i915_request_enable_breadcrumb(request))
> -		intel_engine_queue_breadcrumbs(engine);
> +		intel_engine_signal_breadcrumbs(engine);
>   
>   	__notify_execute_cb(request);
>   
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