Re: [PATCH] drm/i915: Trim NEWCLIENT boosting

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 04/02/2019 15:01, Chris Wilson wrote:
> Limit the NEWCLIENT boost to only give its small priority boost to fresh
> clients only that have no dependencies.
> 
> The idea for using NEWCLIENT boosting, commit b16c765122f9 ("drm/i915:
> Priority boost for new clients"), is that short-lived streams are often
> interactive and require lower latency -- and that by executing those
> ahead of the long running hogs, the short-lived clients do little
> interfere with the system throughput by virtue of their short-lived
> nature. However, we were only considering the client's own timeline for
> determining whether or not it was a fresh stream. This allowed for
> compositors to wake up before their vblank and bump all of its client
> streams. However in testing with media-bench this results in chaining
> all cooperating contexts together preventing us from being able to
> reorder contexts to reduce bubbles (pipeline stalls), overall increasing
> latency, and reducing system throughput. The exact opposite of our
> intent. The compromise of applying the NEWCLIENT boost to strictly fresh
> clients (that do not wait upon anything else) should maintain the
> real-time response under load characteristics of FQ_CODEL, without
> locking together the long chains of dependencies across the system.
> 
> References: b16c765122f9 ("drm/i915: Priority boost for new clients")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>   drivers/gpu/drm/i915/i915_request.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> index d14a1b225f47..04c65e6d83b9 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -980,7 +980,7 @@ void i915_request_add(struct i915_request *request)
>   		 * Allow interactive/synchronous clients to jump ahead of
>   		 * the bulk clients. (FQ_CODEL)
>   		 */
> -		if (!prev || i915_request_completed(prev))
> +		if (list_empty(&request->sched.signalers_list))
>   			attr.priority |= I915_PRIORITY_NEWCLIENT;
>   
>   		engine->schedule(request, &attr);
> 

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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