[Intel-gfx] [PATCH 1/2] drm/i915: Bump wait-times for the final CS interrupt before parking

[Mika Kuoppala]

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

> In the idle worker we drop the prolonged GT wakeref used to cover such
> essentials as interrupt delivery. (When a CS interrupt arrives, we also
> assert that the GT is awake.) However, it turns out that 10ms is not
> long enough to be assured that the last CS interrupt has been delivered,
> so bump that to 200ms, and move the entirety of that wait to before we
> take the struct_mutex to avoid blocking. As this is now a potentially
> long wait, restore the earlier behaviour of bailing out early when a new
> request arrives.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> Cc: Imre Deak <imre.deak at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 31 ++++++++++++++++++++-----------
>  1 file changed, 20 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 026cb52ece0b..d3a638613857 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -3281,8 +3281,8 @@ i915_gem_idle_work_handler(struct work_struct *work)
>  {
>  	struct drm_i915_private *dev_priv =
>  		container_of(work, typeof(*dev_priv), gt.idle_work.work);
> -	struct drm_device *dev = &dev_priv->drm;
>  	bool rearm_hangcheck;
> +	ktime_t end;
>  
>  	if (!READ_ONCE(dev_priv->gt.awake))
>  		return;
> @@ -3291,14 +3291,22 @@ i915_gem_idle_work_handler(struct work_struct *work)
>  	 * Wait for last execlists context complete, but bail out in case a
>  	 * new request is submitted.
>  	 */
> -	wait_for(intel_engines_are_idle(dev_priv), 10);
> -	if (READ_ONCE(dev_priv->gt.active_requests))
> -		return;
> +	end = ktime_add_ms(ktime_get(), 200);
> +	do {
> +		if (READ_ONCE(dev_priv->gt.active_requests) ||
> +		    work_pending(work))
> +			return;
> +
> +		if (intel_engines_are_idle(dev_priv))
> +			break;
> +
> +		usleep_range(100, 500);
> +	} while (ktime_before(ktime_get(), end));
>

Why can't we just wait_for(intel_engines_are_idle(dev_priv, 200)) ?

-Mika

>  	rearm_hangcheck =
>  		cancel_delayed_work_sync(&dev_priv->gpu_error.hangcheck_work);
>  
> -	if (!mutex_trylock(&dev->struct_mutex)) {
> +	if (!mutex_trylock(&dev_priv->drm.struct_mutex)) {
>  		/* Currently busy, come back later */
>  		mod_delayed_work(dev_priv->wq,
>  				 &dev_priv->gt.idle_work,
> @@ -3310,13 +3318,14 @@ i915_gem_idle_work_handler(struct work_struct *work)
>  	 * New request retired after this work handler started, extend active
>  	 * period until next instance of the work.
>  	 */
> -	if (work_pending(work))
> +	if (dev_priv->gt.active_requests || work_pending(work))
>  		goto out_unlock;
>  
> -	if (dev_priv->gt.active_requests)
> -		goto out_unlock;
> -
> -	if (wait_for(intel_engines_are_idle(dev_priv), 10))
> +	/*
> +	 * We are committed now to parking the engines, make sure there
> +	 * will be no more interrupts arriving later.
> +	 */
> +	if (!intel_engines_are_idle(dev_priv))
>  		DRM_ERROR("Timeout waiting for engines to idle\n");
>  
>  	intel_engines_mark_idle(dev_priv);
> @@ -3330,7 +3339,7 @@ i915_gem_idle_work_handler(struct work_struct *work)
>  		gen6_rps_idle(dev_priv);
>  	intel_runtime_pm_put(dev_priv);
>  out_unlock:
> -	mutex_unlock(&dev->struct_mutex);
> +	mutex_unlock(&dev_priv->drm.struct_mutex);
>  
>  out_rearm:
>  	if (rearm_hangcheck) {
> -- 
> 2.15.0.rc1