Re: [PATCH] drm/sched: Increase drm_mock_sched_job_wait_finished timeout when CONFIG_HZ=100

[Tvrtko Ursulin <tvrtko.ursulin@igalia.com>]

On 13/09/2026 09:41, David Gow wrote:
> The drm_sched_scheduler_overhead_tests tests hardcode a timeout of 5x
> total_us, and fail if it's exceeded. However, on systems with
> CONFIG_HZ < 250, this tends to fail.

Systems plural or just UML? I suppose if no hrtimer support and low HZ 
it is plausible since executing the tests needs 1000 x 1ms hrtimer 
callbacks to fire.

Anyway, increasing the tolerance is okay-ish, with the -ish part being 
that it would be even better to skip if test could know before hand on a 
particular system it would be uselessly slow. Hence I am curious whether 
it is just UML or you could point me to other specific platforms/kconfig 
combinations where you saw it fail. In which case maybe we can come up 
with a skip criteria.

Regards,

Tvrtko

> As it's possible to configure many architectures to use 100 Hz (and some,
> such as UML, hardcode CONFIG_HZ=100), increase the timeout so that the test
> doesn't fail on these configurations.
> 
> Fixes: 97ef806a5314 ("drm/sched: Add some scheduling quality unit tests")
> Signed-off-by: David Gow <david@davidgow.net>
> ---
> 
> This failure showed up on UML when testing the addition of CONFIG_DRM to
> the KUnit 'alltests' config[1]. Ideally, I'd like to see this test fixed
> (or at least skipped/disabled) on these broken configurations so that the
> alltests run is clean. (I don't actually run any CONFIG_HZ=100 configs
> other than UML, but fixing them all is ideal if we can manage it.)
> 
> If you'd rather a different implementation / magic number, let me know.
> I picked 15 here as it gave me plenty of leeway: 10 worked most, but not
> all, of the time under i386 qemu w/ CONFIG_HZ_100, and was fine with UML
> on this machine.
> 
> Thanks,
> -- David
> 
> [1]: https://lore.kernel.org/all/20260911-kunit-drm-v1-1-c5c0f18fc7b0@kernel.org/
> ---
>   drivers/gpu/drm/scheduler/tests/tests_scheduler.c | 11 +++++++++--
>   1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/scheduler/tests/tests_scheduler.c b/drivers/gpu/drm/scheduler/tests/tests_scheduler.c
> index 285546a2218f..02c83b5c2189 100644
> --- a/drivers/gpu/drm/scheduler/tests/tests_scheduler.c
> +++ b/drivers/gpu/drm/scheduler/tests/tests_scheduler.c
> @@ -13,6 +13,13 @@
>    * logic.
>    */
>   
> +/* We need a more generous timeout when CONFIG_HZ=100. */
> +#if CONFIG_HZ < 250
> +#define TIMEOUT_MULTIPLIER 15
> +#else
> +#define TIMEOUT_MULTIPLIER 5
> +#endif
> +
>   static int drm_sched_scheduler_init(struct kunit *test)
>   {
>   	struct drm_mock_scheduler *sched;
> @@ -88,7 +95,7 @@ static void drm_sched_scheduler_queue_overhead(struct kunit *test)
>   
>   	/* Wait with a safe margin to avoid every failing. */
>   	done = drm_mock_sched_job_wait_finished(job,
> -						usecs_to_jiffies(total_us) * 5);
> +						usecs_to_jiffies(total_us) * TIMEOUT_MULTIPLIER);
>   	end = ktime_get();
>   	KUNIT_ASSERT_TRUE(test, done);
>   
> @@ -149,7 +156,7 @@ static void drm_sched_scheduler_ping_pong(struct kunit *test)
>   
>   	/* Wait with a safe margin to avoid every failing. */
>   	done = drm_mock_sched_job_wait_finished(job,
> -						usecs_to_jiffies(total_us) * 5);
> +						usecs_to_jiffies(total_us) * TIMEOUT_MULTIPLIER);
>   	end = ktime_get();
>   	KUNIT_ASSERT_TRUE(test, done);
>