Re: [Intel-gfx] [PATCH] drm/i915/selftests: Increase timeout in requests perf selftest

[John Harrison <john.c.harrison@intel.com>]

On 10/11/2021 10:57, Matthew Brost wrote:
> perf_parallel_engines is micro benchmark to test i915 request
> scheduling. The test creates a thread per physical engine and submits
> NOP requests and waits the requests to complete in a loop. In execlists
> mode this works perfectly fine as powerful CPU has enough cores to feed
> each engine and process the CSBs. With GuC submission the uC gets
> overwhelmed as all threads feed into a single CTB channel and the GuC
> gets bombarded with CSBs as contexts are immediately switched in and out
> on the engines due to the zero runtime of the requests. When the GuC is
> overwhelmed scheduling of contexts is unfair due to the nature of the
> GuC scheduling algorithm. This behavior is understood and deemed
> acceptable as this micro benchmark isn't close to real world use case.
> Increasing the timeout of wait period for requests to complete. This
> makes the test understand that is ok for contexts to get starved in this
> scenario.
>
> A future patch / cleanup may just delete these micro benchmark tests as
> they basically mean nothing. We care about real workloads not made up
> ones.
>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>

> ---
>   drivers/gpu/drm/i915/selftests/i915_request.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/selftests/i915_request.c b/drivers/gpu/drm/i915/selftests/i915_request.c
> index d67710d10615..6496671a113c 100644
> --- a/drivers/gpu/drm/i915/selftests/i915_request.c
> +++ b/drivers/gpu/drm/i915/selftests/i915_request.c
> @@ -2805,7 +2805,7 @@ static int p_sync0(void *arg)
>   		i915_request_add(rq);
>   
>   		err = 0;
> -		if (i915_request_wait(rq, 0, HZ / 5) < 0)
> +		if (i915_request_wait(rq, 0, HZ) < 0)
>   			err = -ETIME;
>   		i915_request_put(rq);
>   		if (err)
> @@ -2876,7 +2876,7 @@ static int p_sync1(void *arg)
>   		i915_request_add(rq);
>   
>   		err = 0;
> -		if (prev && i915_request_wait(prev, 0, HZ / 5) < 0)
> +		if (prev && i915_request_wait(prev, 0, HZ) < 0)
>   			err = -ETIME;
>   		i915_request_put(prev);
>   		prev = rq;