[Intel-gfx] [PATCH igt] igt/perf_pmu: Tweak wait_for_rc6, yet again

[Tvrtko Ursulin]

On 07/12/2017 10:35, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2017-12-07 10:25:36)
>>
>> On 06/12/2017 23:12, Chris Wilson wrote:
>>> Still CI remains obstinate that RC6 is not smoothly incrementing during
>>> the sample period. Tweak the wait_for_rc6() to first wait for the
>>> initial Evaluation Interval before polling.
>>>
>>> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
>>> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>>> ---
>>>    tests/perf_pmu.c         | 15 +++++++++++----
>>>    tests/pm_rc6_residency.c | 15 +++++++++++----
>>>    2 files changed, 22 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/tests/perf_pmu.c b/tests/perf_pmu.c
>>> index ff6568221..917832d1b 100644
>>> --- a/tests/perf_pmu.c
>>> +++ b/tests/perf_pmu.c
>>> @@ -1000,13 +1000,20 @@ static bool wait_for_rc6(int fd)
>>>        struct timespec tv = {};
>>>        uint64_t start, now;
>>>    
>>> -     start = pmu_read_single(fd);
>>> +     /* First wait for roughly an RC6 Evaluation Interval */
>>> +     usleep(160 * 1000);
>>> +
>>> +     /* Then poll for RC6 to start ticking */
>>> +     now = pmu_read_single(fd);
>>>        do {
>>> -             usleep(50);
>>> +             start = now;
>>> +             usleep(5000);
>>>                now = pmu_read_single(fd);
>>> -     } while (start == now && !igt_seconds_elapsed(&tv));
>>> +             if (now - start > 2e6)
>>> +                     return true;
>>
>> What is the thinking behind the 2ms of RC6 after 5ms of sleep criteria?
> 
> I was being worried about random fluctuations. The sleep before is
> probably good enough, basically I'm guessing at what caused it to fail,
> with the starting point being that we declared RC6 active before it was.
> 
> 2ms was trying to guess at what the granularity of the counter was,
> which is ~1us, not 1ms. Respin with 2us instead?

Hard for me to say since after the last patch I expected that once the 
counter is running that it is running. Now I don't know anything any 
longer. :/

No harm in trying since the current version is unreliable..

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

Regards,

Tvrtko