Re: [PATCH 2/2] kselftests: timers: Reduce default runtime on inconsistency-check and set-timer-lat

[Shuah Khan <shuahkh@osg.samsung.com>]

On 03/26/2015 10:20 AM, John Stultz wrote:
> On Thu, Mar 26, 2015 at 4:32 AM, Prarit Bhargava <prarit@redhat.com> wrote:
>> On 03/25/2015 07:44 PM, John Stultz wrote:
>>> For the default run_timers target, the timers tests takes the
>>> majority of kselftests runtime.
>>>
>>> So this patch reduces the default runtime for inconsistentcy-check
>>> and set-timer-lat, which reduced the runtime almost in half.
>>>
>>> Before:       11m48.629s
>>> After:        6m47.723s
>>>
>>> Cc: Shuah Khan <shuahkh@osg.samsung.com>
>>> Cc: Prarit Bhargava <prarit@redhat.com>
>>> Cc: Thomas Gleixner <tglx@linutronix.de>
>>> Cc: Richard Cochran <richardcochran@gmail.com>
>>> Signed-off-by: John Stultz <john.stultz@linaro.org>
>>> Signed-off-by: John Stultz <john.stultz@linaro.org>

Same duplicate signature warning on this, no need to re-send.
I will fix it when I apply the patch.

-- Shuah
>>> ---
>>>  tools/testing/selftests/timers/inconsistency-check.c | 2 +-
>>>  tools/testing/selftests/timers/set-timer-lat.c       | 2 +-
>>>  2 files changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/tools/testing/selftests/timers/inconsistency-check.c b/tools/testing/selftests/timers/inconsistency-check.c
>>> index 578e423a..caf1bc9 100644
>>> --- a/tools/testing/selftests/timers/inconsistency-check.c
>>> +++ b/tools/testing/selftests/timers/inconsistency-check.c
>>> @@ -166,7 +166,7 @@ int main(int argc, char *argv[])
>>>       int clockid, opt;
>>>       int userclock = CLOCK_REALTIME;
>>>       int maxclocks = NR_CLOCKIDS;
>>> -     int runtime = 30;
>>> +     int runtime = 10;
>>>       struct timespec ts;
>>>
>>
>> Oops ... left everyone off :)
>>
>> What was the reason that this was originally 30?  Or was that overkill?
> 
> So time inconsistencies (when they manifest, which ideally is never)
> can be fairly rare events. In the past we've seen them due to cpu TSC
> skew and drift, which requires enough scheduler noise to pop the
> process around between cores enough to notice, and enough system
> runtime for the TSCs to drift far enough apart.. Or we've had tiny
> accumulation bugs in update_wall_time which requires the right phase
> in the error accumulation to align with an irq. So the consistency
> test has always been a long running test (originally I'd run it
> overnight), and the 30sec interval here was added just so there was
> some "long enough" interval that wasn't too painful for me to test
> submitted patches with.  Now that more folks are using it (and they
> likely care less), we can cut it down further to avoid making test
> runs too onerous.
> 
> Now, a patch might badly break things and it would be immediately
> obvious to the test that something is wrong, so a quick check isn't
> worthless, but it just doesn't instill that much confidence from me.
> 
> I think as the kselftests grow, we'll have more "types" of test
> targets to run (quick, long, stress, etc), and we can scale the time
> in those tests accordingly. But the default should probably lean
> towards the short side.
> 

Right. I am working on adding support for quick, long etc. The goal
for quick (default) mode is to complete the test runs in 15-20 minutes
to make it easier for developers make it part of the work-flow.

thanks,
-- Shuah

-- 
Shuah Khan
Sr. Linux Kernel Developer
Open Source Innovation Group
Samsung Research America (Silicon Valley)
shuahkh@osg.samsung.com | (970) 217-8978