Re: [Intel-gfx] [PATCH v2] drm/i915/gt: Move the breadcrumb to the signaler if completed upon cancel

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 25/11/2020 19:56, Chris Wilson wrote:
> If while we are cancelling the breadcrumb signaling, we find that the
> request is already completed, move it to the irq signaler and let it be
> signaled.
> 
> v2: Tweak reference counting so that we only acquire a new reference on
> adding to a signal list, as opposed to a hidden i915_request_put of the
> caller's reference.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/gt/intel_breadcrumbs.c | 41 +++++++++++----------
>   1 file changed, 22 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
> index a24cc1ff08a0..00918300f53f 100644
> --- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
> +++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
> @@ -192,18 +192,6 @@ static void add_retire(struct intel_breadcrumbs *b, struct intel_timeline *tl)
>   		intel_engine_add_retire(b->irq_engine, tl);
>   }
>   
> -static bool __signal_request(struct i915_request *rq)
> -{
> -	GEM_BUG_ON(test_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags));
> -
> -	if (!__dma_fence_signal(&rq->fence)) {
> -		i915_request_put(rq);
> -		return false;
> -	}
> -
> -	return true;
> -}
> -
>   static struct llist_node *
>   slist_add(struct llist_node *node, struct llist_node *head)
>   {
> @@ -274,9 +262,11 @@ static void signal_irq_work(struct irq_work *work)
>   			release = remove_signaling_context(b, ce);
>   			spin_unlock(&ce->signal_lock);
>   
> -			if (__signal_request(rq))
> +			if (__dma_fence_signal(&rq->fence))
>   				/* We own signal_node now, xfer to local list */
>   				signal = slist_add(&rq->signal_node, signal);
> +			else
> +				i915_request_put(rq);
>   
>   			if (release) {
>   				add_retire(b, ce->timeline);
> @@ -363,6 +353,17 @@ void intel_breadcrumbs_free(struct intel_breadcrumbs *b)
>   	kfree(b);
>   }
>   
> +static void irq_signal_request(struct i915_request *rq,
> +			       struct intel_breadcrumbs *b)
> +{
> +	if (!__dma_fence_signal(&rq->fence))
> +		return;
> +
> +	i915_request_get(rq);
> +	if (llist_add(&rq->signal_node, &b->signaled_requests))
> +		irq_work_queue(&b->irq_work);
> +}
> +
>   static void insert_breadcrumb(struct i915_request *rq)
>   {
>   	struct intel_breadcrumbs *b = READ_ONCE(rq->engine)->breadcrumbs;
> @@ -372,17 +373,13 @@ static void insert_breadcrumb(struct i915_request *rq)
>   	if (test_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags))
>   		return;
>   
> -	i915_request_get(rq);
> -
>   	/*
>   	 * 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) &&
> -		    llist_add(&rq->signal_node, &b->signaled_requests))
> -			irq_work_queue(&b->irq_work);
> +		irq_signal_request(rq, b);
>   		return;
>   	}
>   
> @@ -413,6 +410,8 @@ static void insert_breadcrumb(struct i915_request *rq)
>   				break;
>   		}
>   	}
> +
> +	i915_request_get(rq);
>   	list_add_rcu(&rq->signal_link, pos);
>   	GEM_BUG_ON(!check_signal_order(ce, rq));
>   	GEM_BUG_ON(test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &rq->fence.flags));
> @@ -453,6 +452,7 @@ bool i915_request_enable_breadcrumb(struct i915_request *rq)
>   
>   void i915_request_cancel_breadcrumb(struct i915_request *rq)
>   {
> +	struct intel_breadcrumbs *b = READ_ONCE(rq->engine)->breadcrumbs;
>   	struct intel_context *ce = rq->context;
>   	bool release;
>   
> @@ -461,11 +461,14 @@ void i915_request_cancel_breadcrumb(struct i915_request *rq)
>   
>   	spin_lock(&ce->signal_lock);
>   	list_del_rcu(&rq->signal_link);
> -	release = remove_signaling_context(rq->engine->breadcrumbs, ce);
> +	release = remove_signaling_context(b, ce);
>   	spin_unlock(&ce->signal_lock);
>   	if (release)
>   		intel_context_put(ce);
>   
> +	if (__request_completed(rq))
> +		irq_signal_request(rq, b);
> +
>   	i915_request_put(rq);
>   }
>   
> 

I can follow this more easily, thanks!

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

Regards,

Tvrtko
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