Re: [igt-dev] [Intel-gfx] [PATCH i-g-t 5/6] tests/gem_eio: Only wait-for-idle inside trigger_reset()

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

On 14/05/2018 09:02, Chris Wilson wrote:
> trigger_reset() imposes a tight time constraint (2s) so that we verify
> that the reset itself completes quickly. In the middle of this check, we
> call gem_quiescent_gpu() which may invoke an rcu_barrier() or two to
> clear out the freed memory (DROP_FREED). Those barriers may have
> unbounded latency pushing beyond the 2s timeout, so restrict the
> operation to only wait-for-idle (DROP_ACTIVE).
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105957
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>   tests/gem_eio.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/tests/gem_eio.c b/tests/gem_eio.c
> index 4720b47b5..e1aff639d 100644
> --- a/tests/gem_eio.c
> +++ b/tests/gem_eio.c
> @@ -74,8 +74,7 @@ static void trigger_reset(int fd)
>   	/* And just check the gpu is indeed running again */
>   	igt_debug("Checking that the GPU recovered\n");
>   	gem_test_engine(fd, ALL_ENGINES);
> -
> -	gem_quiescent_gpu(fd);
> +	igt_drop_caches_set(fd, DROP_ACTIVE);
>   
>   	/* We expect forced reset and health check to be quick. */
>   	igt_assert(igt_seconds_elapsed(&ts) < 2);
> 

Sounds fine to only wait for idle:

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

However I am a bit surprised that under plain IGT environment RCU 
latency can be so high.

Regards,

Tvrtko
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