[Intel-gfx] [PATCH 2/3] drm/i915/execlists: Push the tasklet kick after reset to reset_finish

[Tvrtko Ursulin]

On 04/06/2018 08:34, Chris Wilson wrote:
> In the unlikely case where we have failed to keep submitting to the GPU,
> we end up with the ELSP queue empty but a pending queue of requests.

How does this happen? We have nothing in ports but a queue of requests, 
but we managed to declare a GPU hang, even though there is nothing in 
ports so GPU looks idle from the outside?

Regards,

Tvrtko

> Here, we skip the per-engine reset as there is no guilty request, but in
> doing so we also skip the engine restart leaving ourselves with a
> permanently hung engine. A quick way to recover is by moving the tasklet
> kick to execlists_reset_finish() (from init_hw). We still emit the error
> on hanging, so the error is not lost but we should be able to recover.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala at intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Cc: Michel Thierry <michel.thierry at intel.com>
> ---
>   drivers/gpu/drm/i915/intel_lrc.c | 13 +++++++------
>   1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 8d912d0c8fc1..c8d9b5aed94a 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -1803,7 +1803,6 @@ static bool unexpected_starting_state(struct intel_engine_cs *engine)
>   
>   static int gen8_init_common_ring(struct intel_engine_cs *engine)
>   {
> -	struct intel_engine_execlists * const execlists = &engine->execlists;
>   	int ret;
>   
>   	ret = intel_mocs_init_engine(engine);
> @@ -1821,10 +1820,6 @@ static int gen8_init_common_ring(struct intel_engine_cs *engine)
>   
>   	enable_execlists(engine);
>   
> -	/* After a GPU reset, we may have requests to replay */
> -	if (execlists->first)
> -		tasklet_schedule(&execlists->tasklet);
> -
>   	return 0;
>   }
>   
> @@ -2006,6 +2001,12 @@ static void execlists_reset(struct intel_engine_cs *engine,
>   
>   static void execlists_reset_finish(struct intel_engine_cs *engine)
>   {
> +	struct intel_engine_execlists * const execlists = &engine->execlists;
> +
> +	/* After a GPU reset, we may have requests to replay */
> +	if (execlists->first)
> +		tasklet_schedule(&execlists->tasklet);
> +
>   	/*
>   	 * Flush the tasklet while we still have the forcewake to be sure
>   	 * that it is not allowed to sleep before we restart and reload a
> @@ -2015,7 +2016,7 @@ static void execlists_reset_finish(struct intel_engine_cs *engine)
>   	 * serialising multiple attempts to reset so that we know that we
>   	 * are the only one manipulating tasklet state.
>   	 */
> -	__tasklet_enable_sync_once(&engine->execlists.tasklet);
> +	__tasklet_enable_sync_once(&execlists->tasklet);
>   
>   	GEM_TRACE("%s\n", engine->name);
>   }
>