[Intel-gfx] [PATCH v2 25/28] drm/i915: Interrupt driven request completion

[Daniel, Thomas]

> -----Original Message-----
> From: Intel-gfx [mailto:intel-gfx-bounces at lists.freedesktop.org] On Behalf
> Of John.C.Harrison at Intel.com
> Sent: Friday, November 14, 2014 12:19 PM
> To: Intel-GFX at Lists.FreeDesktop.Org
> Subject: [Intel-gfx] [PATCH v2 25/28] drm/i915: Interrupt driven request
> completion
> 
> From: John Harrison <John.C.Harrison at Intel.com>
> 
> Added a hook to the ring noftification code to process request completion.
> This means that there is no longer a need to explicitly process request
> completions every time a request object is tested. Instead, the test code
> simply becomes 'return req->completed'. Obviously, this only works if ring
> interrupts are enabled, however, this is already the case for the duration of
> __wait_request() which is the point where the driver really needs to know.
> 
> To prevent stale requests floating around indefinitely, the retire work
> handler also now performs a completion check periodically.
> 
> For: VIZ-4377
> Signed-off-by: John Harrison <John.C.Harrison at Intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.h |    5 -----
>  drivers/gpu/drm/i915/i915_gem.c |   10 ++++++++++
>  drivers/gpu/drm/i915/i915_irq.c |    2 ++
>  3 files changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h
> b/drivers/gpu/drm/i915/i915_drv.h index 8531e0f..66219b5 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2072,11 +2072,6 @@ static inline void i915_gem_request_assign(struct
> drm_i915_gem_request **pdst,  static inline bool
> i915_gem_request_completed(struct drm_i915_gem_request *req,
>  					      bool lazy_coherency)
>  {
> -	if (req->complete)
> -		return true;
> -
> -	i915_gem_complete_requests_ring(req->ring, lazy_coherency);
> -
>  	return req->complete;
>  }
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c
> b/drivers/gpu/drm/i915/i915_gem.c index edf712b..039dbb8 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1264,6 +1264,11 @@ int __i915_wait_request(struct
> drm_i915_gem_request *req,
>  	if (!irq_test_in_progress && WARN_ON(!ring->irq_get(ring)))
>  		return -ENODEV;
> 
> +	/* Completion status should be interrupt driven but it is possible
> +	 * the request popped out before the interrupt was enabled. So do
> an
> +	 * explicit check now... */
> +	i915_gem_complete_requests_ring(req->ring, false);
> +
>  	/* Record current time in case interrupted by signal, or wedged */
>  	trace_i915_gem_request_wait_begin(req);
>  	before = ktime_get_raw_ns();
> @@ -2487,6 +2492,10 @@ int __i915_add_request(struct intel_engine_cs
> *ring,
>  	list_add_tail(&request->list, &ring->request_list);
>  	request->file_priv = NULL;
> 
> +	/* Avoid race condition where the request completes before it has
> +	 * been added to the list. */
> +	ring->last_read_seqno = 0;
> +
>  	if (file) {
>  		struct drm_i915_file_private *file_priv = file->driver_priv;
> 
> @@ -2858,6 +2867,7 @@ i915_gem_retire_requests(struct drm_device
> *dev)
>  	int i;
> 
>  	for_each_ring(ring, dev_priv, i) {
> +		i915_gem_complete_requests_ring(ring, false);
>  		i915_gem_retire_requests_ring(ring);
>  		idle &= list_empty(&ring->request_list);
>  	}
> diff --git a/drivers/gpu/drm/i915/i915_irq.c
> b/drivers/gpu/drm/i915/i915_irq.c index 198bbc6..4f63966 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -987,6 +987,8 @@ static void notify_ring(struct drm_device *dev,
> 
>  	trace_i915_gem_request_complete(ring);
> 
> +	i915_gem_complete_requests_ring(ring, false);
I915_gem_complete_requests_ring takes the request list lock and iterates over the entire list.  Are you sure this is safe to do during the interrupt handler?

Thomas.

> +
>  	wake_up_all(&ring->irq_queue);
>  	i915_queue_hangcheck(dev);
>  }
> --
> 1.7.9.5
> 
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