Re: [PATCH 01/10] drm/i915/breadcrumbs: Queue hangcheck before sleeping

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> Never go to sleep waiting on the GPU without first ensuring that we will
> get woken up.
>
> We have a choice of queuing the hangcheck before every schedule() or the
> first time we wakeup. In order to simply accommodate both the signaler
> and the ordinary waiter, move the queuing to the common point of
> enabling the irq. We lose the paranoid safety of ensuring that the
> hangcheck is active before the sleep, but avoid code duplication (and
> redundant hangcheck queuing).
>
> Testcase: igt/prime_busy
> Fixes: c81d46138da6 ("drm/i915: Convert trace-irq to the breadcrumb waiter")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>

> ---
>  drivers/gpu/drm/i915/i915_gem.c          | 9 ---------
>  drivers/gpu/drm/i915/intel_breadcrumbs.c | 9 +++++++++
>  2 files changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 8f50919ba9b4..7fd44980798f 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1501,15 +1501,6 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
>  			break;
>  		}
>  
> -		/* Ensure that even if the GPU hangs, we get woken up.
> -		 *
> -		 * However, note that if no one is waiting, we never notice
> -		 * a gpu hang. Eventually, we will have to wait for a resource
> -		 * held by the GPU and so trigger a hangcheck. In the most
> -		 * pathological case, this will be upon memory starvation!
> -		 */
> -		i915_queue_hangcheck(req->i915);
> -
>  		timeout_remain = io_schedule_timeout(timeout_remain);
>  		if (timeout_remain == 0) {
>  			ret = -ETIME;
> diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
> index d89b2c963618..b074f3d6d127 100644
> --- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
> +++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
> @@ -93,6 +93,15 @@ static void __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)
>  	if (!b->irq_enabled ||
>  	    test_bit(engine->id, &i915->gpu_error.missed_irq_rings))
>  		mod_timer(&b->fake_irq, jiffies + 1);
> +
> +	/* Ensure that even if the GPU hangs, we get woken up.
> +	 *
> +	 * However, note that if no one is waiting, we never notice
> +	 * a gpu hang. Eventually, we will have to wait for a resource
> +	 * held by the GPU and so trigger a hangcheck. In the most
> +	 * pathological case, this will be upon memory starvation!
> +	 */
> +	i915_queue_hangcheck(i915);
>  }
>  
>  static void __intel_breadcrumbs_disable_irq(struct intel_breadcrumbs *b)
> -- 
> 2.8.1
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