Re: [PATCH] drm/i915: Move tasklet kicking to __i915_request_queue caller

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

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

> Since __i915_request_queue() may be called from hardirq (timer) context,
> we cannot use local_bh_disable/enable at the lower level. As we do want
> to kick the tasklet to speed up initial submission or preemption for
> normal client submission, lift it to the normal process context
> callpath.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_request.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> index 4021334dd2c5..8a2bc1d317e4 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -1203,12 +1203,10 @@ void __i915_request_queue(struct i915_request *rq,
>  	 * decide whether to preempt the entire chain so that it is ready to
>  	 * run at the earliest possible convenience.
>  	 */
> -	local_bh_disable();
>  	i915_sw_fence_commit(&rq->semaphore);
>  	if (attr && rq->engine->schedule)
>  		rq->engine->schedule(rq, attr);
>  	i915_sw_fence_commit(&rq->submit);
> -	local_bh_enable(); /* Kick the execlists tasklet if just scheduled */

Was this here to only optimize the latency from schedule
to resubmission?

Or is it actually guarding something?

-Mika

>  }
>  
>  void i915_request_add(struct i915_request *rq)
> @@ -1247,7 +1245,9 @@ void i915_request_add(struct i915_request *rq)
>  	if (list_empty(&rq->sched.signalers_list))
>  		attr.priority |= I915_PRIORITY_WAIT;
>  
> +	local_bh_disable();
>  	__i915_request_queue(rq, &attr);
> +	local_bh_enable(); /* Kick the execlists tasklet if just scheduled */
>  
>  	/*
>  	 * In typical scenarios, we do not expect the previous request on
> -- 
> 2.23.0.rc1
>
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