Re: [igt-dev] [PATH i-g-t 04/13] gem_wsim: Check sleep times

Tvrtko Ursulin
2018-09-07T16:00:39Z

On 07/09/2018 15:13, Ville Syrjälä wrote:
> On Fri, Sep 07, 2018 at 09:45:14AM +0100, Chris Wilson wrote:
>> Quoting Tvrtko Ursulin (2018-09-07 09:37:00)
>>>
>>> On 05/09/2018 15:09, Ville Syrjälä wrote:
>>>> On Wed, Sep 05, 2018 at 02:49:30PM +0100, Tvrtko Ursulin wrote:
>>>>> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>>>>
>>>>> Notice in more places if we are running behind.
>>>>>
>>>>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>>>> ---
>>>>> benchmarks/gem_wsim.c | 52 ++++++++++++++++++++++++++++++++++++++-----
>>>>> 1 file changed, 46 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/benchmarks/gem_wsim.c b/benchmarks/gem_wsim.c
>>>>> index 25af4d678ba4..b05e9760f419 100644
>>>>> --- a/benchmarks/gem_wsim.c
>>>>> +++ b/benchmarks/gem_wsim.c
>>>>> @@ -1718,6 +1718,21 @@ static bool sync_deps(struct workload *wrk, struct w_step *w)
>>>>> return synced;
>>>>> }
>>>>>
>>>>> +static unsigned int measured_usleep(unsigned int usec)
>>>>> +{
>>>>> + struct timespec ts = { };
>>>>> + unsigned int slept;
>>>>> +
>>>>> + slept = igt_nsec_elapsed(&ts);
>>>>> + igt_assert(slept == 0);
>>>>> + do {
>>>>> + usleep(usec - slept);
>>>>> + slept = igt_nsec_elapsed(&ts) / 1000;
>>>>> + } while (slept < usec);
>>>>
>>>> clock_nanosleep(ABS)?
>>>
>>> Hm I think I see what you mean. Rather than a relative sleep trying to
>>> hit the loop period, ask from the kernel (or glibc, I don't know who
>>> implements it) to sleep until an absolute target. This totally makes
>>> sense and would simplify the code from one angle, I am just not sure if
>>> absolute sleep can be relied upon any better to not oversleep. Well,
>>> actually for scheduling delays not to affect the caller. However maybe
>>> it doesn't matter since AFAIR my main problem were dropped period due
>>> GPU activity (the first pair of warning messages in the patch), and
>>> again AFAIR, it was quite hard to hit the second ones.
>>
>> Right, it removes the loop but we still want to keep the measurement.
>
> I guess we still want a loop if we're worried about signals? Not sure
> why else we'd need a loop anyway. But the loop could be just something
> like 'while (clock_nanosleep()) ;'

In this case just a case of copying measured_usleep verbatim from
another test because it was easy. Otherwise I think it's fine what you
suggest, especially since Chris also complained about using igt helpers
from outside tests/. So I'll respin to that effect.

Regards,

Tvrtko