Re: [Intel-gfx] [PATCH 2/2] drm/i915/gt: Skip over completed active execlists, again

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

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

> Now that we are careful to always force-restore contexts upon rewinding
> (where necessary), we can restore our optimisation to skip over
> completed active execlists when dequeuing.
>
> Referenecs: 35f3fd8182ba ("drm/i915/execlists: Workaround switching back to a completed context")
> References: 8ab3a3812aa9 ("drm/i915/gt: Incrementally check for rewinding")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>

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

> ---
>  .../drm/i915/gt/intel_execlists_submission.c  | 34 +++++++++----------
>  1 file changed, 16 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> index 524c8b54d220..ac1be7a632d3 100644
> --- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> +++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> @@ -1224,12 +1224,20 @@ static void set_preempt_timeout(struct intel_engine_cs *engine,
>  		     active_preempt_timeout(engine, rq));
>  }
>  
> +static bool completed(const struct i915_request *rq)
> +{
> +	if (i915_request_has_sentinel(rq))
> +		return false;
> +
> +	return __i915_request_is_complete(rq);
> +}
> +
>  static void execlists_dequeue(struct intel_engine_cs *engine)
>  {
>  	struct intel_engine_execlists * const execlists = &engine->execlists;
>  	struct i915_request **port = execlists->pending;
>  	struct i915_request ** const last_port = port + execlists->port_mask;
> -	struct i915_request *last = *execlists->active;
> +	struct i915_request *last, * const *active;
>  	struct virtual_engine *ve;
>  	struct rb_node *rb;
>  	bool submit = false;
> @@ -1266,21 +1274,13 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>  	 * i.e. we will retrigger preemption following the ack in case
>  	 * of trouble.
>  	 *
> -	 * In theory we can skip over completed contexts that have not
> -	 * yet been processed by events (as those events are in flight):
> -	 *
> -	 * while ((last = *active) && i915_request_completed(last))
> -	 *	active++;
> -	 *
> -	 * However, the GPU cannot handle this as it will ultimately
> -	 * find itself trying to jump back into a context it has just
> -	 * completed and barf.
>  	 */
> +	active = execlists->active;
> +	while ((last = *active) && completed(last))
> +		active++;
>  
>  	if (last) {
> -		if (__i915_request_is_complete(last)) {
> -			goto check_secondary;
> -		} else if (need_preempt(engine, last)) {
> +		if (need_preempt(engine, last)) {
>  			ENGINE_TRACE(engine,
>  				     "preempting last=%llx:%lld, prio=%d, hint=%d\n",
>  				     last->fence.context,
> @@ -1359,9 +1359,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>  			 * we hopefully coalesce several updates into a single
>  			 * submission.
>  			 */
> -check_secondary:
> -			if (!list_is_last(&last->sched.link,
> -					  &engine->active.requests)) {
> +			if (active[1]) {
>  				/*
>  				 * Even if ELSP[1] is occupied and not worthy
>  				 * of timeslices, our queue might be.
> @@ -1562,7 +1560,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>  	 * of ordered contexts.
>  	 */
>  	if (submit &&
> -	    memcmp(execlists->active,
> +	    memcmp(active,
>  		   execlists->pending,
>  		   (port - execlists->pending) * sizeof(*port))) {
>  		*port = NULL;
> @@ -1570,7 +1568,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>  			execlists_schedule_in(*port, port - execlists->pending);
>  
>  		WRITE_ONCE(execlists->yield, -1);
> -		set_preempt_timeout(engine, *execlists->active);
> +		set_preempt_timeout(engine, *active);
>  		execlists_submit_ports(engine);
>  	} else {
>  		ring_set_paused(engine, 0);
> -- 
> 2.20.1
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