[Intel-gfx] [PATCH v2 3/3] drm/i915: Defer declaration of missed-interrupt until the waiter is asleep

[Tvrtko Ursulin]

On 17/02/2017 10:18, Chris Wilson wrote:
> If the waiter was currently running, assume it hasn't had a chance
> to process the pending interupt (e.g, low priority task on a loaded
> system) and wait until it sleeps before declaring a missed interrupt.
>
> References: https://bugs.freedesktop.org/show_bug.cgi?id=99816
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_breadcrumbs.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
> index 4395b177493e..2ad29fb77b2d 100644
> --- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
> +++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
> @@ -45,6 +45,15 @@ static void intel_breadcrumbs_hangcheck(unsigned long data)
>  		return;
>  	}
>
> +	/* If the waiter was currently running, assume it hasn't had a chance
> +	 * to process the pending interupt (e.g, low priority task on a loaded
> +	 * system) and wait until it sleeps before declaring a missed interrupt.
> +	 */
> +	if (!intel_engine_wakeup(engine)) {
> +		mod_timer(&b->hangcheck, wait_timeout());
> +		return;
> +	}
> +
>  	DRM_DEBUG("Hangcheck timer elapsed... %s idle\n", engine->name);
>  	set_bit(engine->id, &engine->i915->gpu_error.missed_irq_rings);
>  	mod_timer(&engine->breadcrumbs.fake_irq, jiffies + 1);
>

Change here is that we would never declare a GPU hang is userspace would 
just wait indefinitely, or in other words with this patch we would rely 
on userspace timing out on their waits in order to declare a hang.

Hm, in fact even with the current code, if the userspace keeps exiting 
and re-entering the wait we would be re-arming the hangcheck timer and 
so also never notice a GPU hang.

Regards,

Tvrtko