Re: [PATCH 03/10] drm/i915/gt: Replace intel_engine_transfer_stale_breadcrumbs

[Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>]

On 20/07/2020 10:23, Chris Wilson wrote:
> After staring at the breadcrumb enabling/cancellation and coming to the
> conclusion that the cause of the mysterious stale breadcrumbs must the
> act of submitting a completed requests, we can then redirect those
> completed requests onto a dedicated signaled_list at the time of
> construction and so eliminate intel_engine_transfer_stale_breadcrumbs().
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

Regards,

Tvrtko

> ---
>   drivers/gpu/drm/i915/gt/intel_breadcrumbs.c | 50 ++++++++-------------
>   drivers/gpu/drm/i915/gt/intel_engine.h      |  3 --
>   drivers/gpu/drm/i915/gt/intel_lrc.c         | 15 -------
>   drivers/gpu/drm/i915/i915_request.c         |  5 +--
>   4 files changed, 21 insertions(+), 52 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
> index 3d211a0c2b5a..fbdc465a5870 100644
> --- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
> +++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
> @@ -142,16 +142,16 @@ static void add_retire(struct intel_breadcrumbs *b, struct intel_timeline *tl)
>   	intel_engine_add_retire(engine, tl);
>   }
>   
> -static void __signal_request(struct i915_request *rq, struct list_head *signals)
> +static bool __signal_request(struct i915_request *rq, struct list_head *signals)
>   {
> -	GEM_BUG_ON(!test_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags));
>   	clear_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags);
>   
>   	if (!__dma_fence_signal(&rq->fence))
> -		return;
> +		return false;
>   
>   	i915_request_get(rq);
>   	list_add_tail(&rq->signal_link, signals);
> +	return true;
>   }
>   
>   static void signal_irq_work(struct irq_work *work)
> @@ -278,32 +278,6 @@ void intel_engine_reset_breadcrumbs(struct intel_engine_cs *engine)
>   	spin_unlock_irqrestore(&b->irq_lock, flags);
>   }
>   
> -void intel_engine_transfer_stale_breadcrumbs(struct intel_engine_cs *engine,
> -					     struct intel_context *ce)
> -{
> -	struct intel_breadcrumbs *b = &engine->breadcrumbs;
> -	unsigned long flags;
> -
> -	spin_lock_irqsave(&b->irq_lock, flags);
> -	if (!list_empty(&ce->signals)) {
> -		struct i915_request *rq, *next;
> -
> -		/* Queue for executing the signal callbacks in the irq_work */
> -		list_for_each_entry_safe(rq, next, &ce->signals, signal_link) {
> -			GEM_BUG_ON(rq->engine != engine);
> -			GEM_BUG_ON(!__request_completed(rq));
> -
> -			__signal_request(rq, &b->signaled_requests);
> -		}
> -
> -		INIT_LIST_HEAD(&ce->signals);
> -		list_del_init(&ce->signal_link);
> -
> -		irq_work_queue(&b->irq_work);
> -	}
> -	spin_unlock_irqrestore(&b->irq_lock, flags);
> -}
> -
>   void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine)
>   {
>   }
> @@ -317,6 +291,17 @@ static void insert_breadcrumb(struct i915_request *rq,
>   	if (test_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags))
>   		return;
>   
> +	/*
> +	 * If the request is already completed, we can transfer it
> +	 * straight onto a signaled list, and queue the irq worker for
> +	 * its signal completion.
> +	 */
> +	if (__request_completed(rq)) {
> +		if (__signal_request(rq, &b->signaled_requests))
> +			irq_work_queue(&b->irq_work);
> +		return;
> +	}
> +
>   	__intel_breadcrumbs_arm_irq(b);
>   
>   	/*
> @@ -344,8 +329,11 @@ static void insert_breadcrumb(struct i915_request *rq,
>   	if (pos == &ce->signals) /* catch transitions from empty list */
>   		list_move_tail(&ce->signal_link, &b->signalers);
>   	GEM_BUG_ON(!check_signal_order(ce, rq));
> -
>   	set_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags);
> +
> +	/* Check after attaching to irq, interrupt may have already fired. */
> +	if (__request_completed(rq))
> +		irq_work_queue(&b->irq_work);
>   }
>   
>   bool i915_request_enable_breadcrumb(struct i915_request *rq)
> @@ -401,7 +389,7 @@ bool i915_request_enable_breadcrumb(struct i915_request *rq)
>   
>   	spin_unlock(&b->irq_lock);
>   
> -	return !__request_completed(rq);
> +	return true;
>   }
>   
>   void i915_request_cancel_breadcrumb(struct i915_request *rq)
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine.h b/drivers/gpu/drm/i915/gt/intel_engine.h
> index a9249a23903a..faf00a353e25 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine.h
> +++ b/drivers/gpu/drm/i915/gt/intel_engine.h
> @@ -237,9 +237,6 @@ intel_engine_signal_breadcrumbs(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);
>   
> -void intel_engine_transfer_stale_breadcrumbs(struct intel_engine_cs *engine,
> -					     struct intel_context *ce);
> -
>   void intel_engine_print_breadcrumbs(struct intel_engine_cs *engine,
>   				    struct drm_printer *p);
>   
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index 21c16e31c4fe..88a5c155154d 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -1805,18 +1805,6 @@ static bool virtual_matches(const struct virtual_engine *ve,
>   	return true;
>   }
>   
> -static void virtual_xfer_breadcrumbs(struct virtual_engine *ve)
> -{
> -	/*
> -	 * All the outstanding signals on ve->siblings[0] must have
> -	 * been completed, just pending the interrupt handler. As those
> -	 * signals still refer to the old sibling (via rq->engine), we must
> -	 * transfer those to the old irq_worker to keep our locking
> -	 * consistent.
> -	 */
> -	intel_engine_transfer_stale_breadcrumbs(ve->siblings[0], &ve->context);
> -}
> -
>   #define for_each_waiter(p__, rq__) \
>   	list_for_each_entry_lockless(p__, \
>   				     &(rq__)->sched.waiters_list, \
> @@ -2275,9 +2263,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>   					virtual_update_register_offsets(regs,
>   									engine);
>   
> -				if (!list_empty(&ve->context.signals))
> -					virtual_xfer_breadcrumbs(ve);
> -
>   				/*
>   				 * Move the bound engine to the top of the list
>   				 * for future execution. We then kick this
> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> index 58e37f96ae21..ada630677cf3 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -592,9 +592,8 @@ bool __i915_request_submit(struct i915_request *request)
>   	 */
>   	__notify_execute_cb_irq(request);
>   
> -	if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &request->fence.flags) &&
> -	    !i915_request_enable_breadcrumb(request))
> -		intel_engine_signal_breadcrumbs(engine);
> +	if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &request->fence.flags))
> +		i915_request_enable_breadcrumb(request);
>   
>   	return result;
>   }
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