Re: [PATCH v2] drm/i915: Speed up idle detection by kicking the tasklets

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

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

> We rely on ksoftirqd to run in a timely fashion in order to drain the
> execlists queue. Quite frequently, it does not. In some cases we may see
> latencies of over 200ms triggering our idle timeouts and forcing us to
> declare the driver wedged!
>
> Thus we can speed up idle detection by bypassing ksoftirqd in these
> cases and flush our tasklet to confirm if we are indeed still waiting
> for the ELSP to drain.
>
> v2: Put the execlists.first check back; it is required for handling
> reset!
>
> References: https://bugs.freedesktop.org/show_bug.cgi?id=106373
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_engine_cs.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
> index 70325e0824e3..a3111511ea1d 100644
> --- a/drivers/gpu/drm/i915/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/intel_engine_cs.c
> @@ -945,10 +945,19 @@ bool intel_engine_is_idle(struct intel_engine_cs *engine)
>  		return true;
>  
>  	/* Waiting to drain ELSP? */
> -	if (READ_ONCE(engine->execlists.active))
> -		return false;
> +	if (READ_ONCE(engine->execlists.active)) {
> +		struct intel_engine_execlists *execlists = &engine->execlists;
> +
> +		if (tasklet_trylock(&execlists->tasklet)) {

Now that we have the lock, sample active again to catch
the late tasklet run and skip running if so?

-Mika

> +			execlists->tasklet.func(execlists->tasklet.data);
> +			tasklet_unlock(&execlists->tasklet);
> +		}
> +
> +		if (READ_ONCE(execlists->active))
> +			return false;
> +	}
>  
> -	/* ELSP is empty, but there are ready requests? */
> +	/* ELSP is empty, but there are ready requests? E.g. after reset */
>  	if (READ_ONCE(engine->execlists.first))
>  		return false;
>  
> -- 
> 2.17.0
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