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

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

On 14/09/2026 11:06, David Gow wrote:
> Le 14/09/2026 à 4:49 PM, Tvrtko Ursulin a écrit :
>>
>> 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.
> 
> UML is the most important of the ones I tested (as it doesn't have a way
> to increase HZ, though it did pass if I manually forced CONFIG_HZ=1000),
> but even x86/x86_64 will trigger this if CONFIG_HZ_100=y.
> 
> For example, I can reproduce it with:
> ./tools/testing/kunit/kunit.py run --arch x86_64 --kconfig_add CONFIG_DRM=y --kconfig_add CONFIG_HZ_100=y drm_sched_scheduler_overhead_tests

Right, I even developed the tests with that setup, just under arm64 and 
the default HZ=250.
  >> 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.
> 
> I saw it passing relatively consistently on x86 (under qemu) with
> CONFIG_HZ=250, and failing consistently on everything with
> CONFIG_HZ=100.
> I don't think it'd be a problem to either have the test depend
> on CONFIG_HZ >= 250 or use that as criteria to skip the test
> altogether.
> 
> I'm happy to send out a v2 of this patch which just uses the same
> criteria (CONFIG_HZ < 250) to just skip the test if you'd prefer.

I suspect the real condition would be HZ < 250 && 
something-like-!hrtimer_highres_enabled, but as the latter is not 
exported for modules I have no smart ideas. It's not a loss really to 
skip the scheduling quality tests on more platforms than strictly 
required so I'd say lets go with that.

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);
>>>    
>>
>