Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler utilization data
From: Rafael J. Wysocki
Date: Thu Mar 03 2016 - 15:20:23 EST
On Thu, Mar 3, 2016 at 9:06 PM, Steve Muckle <steve.muckle@xxxxxxxxxx> wrote:
> On 03/03/2016 05:07 AM, Vincent Guittot wrote:
>> I mainly want to prevent any useless and periodic frequency switch
>> because of an utilization that changes with the current frequency (if
>> frequency invariance is not used) and that can make the formula
>> selects another frequency than the current one. That what i can see
>> when testing it .
>>
>> Sorry for the late reply, i was trying to do some test on my board but
>> was facing some crash issue (not link with your patchset). So i have
>> done some tests and i can see such instable behavior. I have generated
>> a load of 33% at max frequency (3ms runs every 9ms) and i can see the
>> frequency that toggles without any good reason. Saying that, i can see
>> similar thing with ondemand.
>
> FWIW I ran some performance numbers on my chromebook 2. Initially I
> forgot to bring in the frequency invariance support but that yielded an
> opportunity to see the impact of it.
>
> The tests below consist of a periodic workload. The OH (overhead)
> numbers show how close the workload got to running as slow as fmin (100%
> = as slow as powersave gov, 0% = as fast as perf gov). The OR (overrun)
> number is the count of instances where the busy work exceeded the period.
>
> First a comparison of schedutil with and without frequency invariance.
> Run and period are in milliseconds.
>
> scu (no inv) scu (w/inv)
> run period busy % OR OH OR OH
> 1 100 1.00% 0 79.72% 0 95.86%
> 10 1000 1.00% 0 24.52% 0 71.61%
> 1 10 10.00% 0 21.25% 0 41.78%
> 10 100 10.00% 0 26.06% 0 47.96%
> 100 1000 10.00% 0 6.36% 0 26.03%
> 6 33 18.18% 0 15.67% 0 31.61%
> 66 333 19.82% 0 8.94% 0 29.46%
> 4 10 40.00% 0 6.26% 0 12.93%
> 40 100 40.00% 0 6.93% 2 14.08%
> 400 1000 40.00% 0 1.65% 0 11.58%
> 5 9 55.56% 0 3.70% 0 7.70%
> 50 90 55.56% 1 4.19% 6 8.06%
> 500 900 55.56% 0 1.35% 5 6.94%
> 9 12 75.00% 0 1.60% 56 3.59%
> 90 120 75.00% 0 1.88% 21 3.94%
> 900 1200 75.00% 0 0.73% 4 4.41%
>
> Frequency invariance causes schedutil overhead to increase noticeably. I
> haven't dug into traces or anything. Perhaps this is due to the
> algorithm overshooting then overcorrecting etc., I do not yet know.
So as I said, the formula I used didn't take invariance into account,
so that's quite as expected.
> Here is a comparison, with frequency invariance, of ondemand and
> interactive with schedfreq and schedutil. The first two columns (run and
> period) are omitted so the table will fit.
>
> ondemand interactive schedfreq schedutil
> busy % OR OH OR OH OR OH OR OH
> 1.00% 0 68.96% 0 100.04% 0 78.49% 0 95.86%
> 1.00% 0 25.04% 0 22.59% 0 72.56% 0 71.61%
> 10.00% 0 21.75% 0 63.08% 0 52.40% 0 41.78%
> 10.00% 0 12.17% 0 14.41% 0 17.33% 0 47.96%
> 10.00% 0 2.57% 0 2.17% 0 0.29% 0 26.03%
> 18.18% 0 12.39% 0 9.39% 0 17.34% 0 31.61%
> 19.82% 0 3.74% 0 3.42% 0 12.26% 0 29.46%
> 40.00% 2 6.26% 1 12.23% 0 6.15% 0 12.93%
> 40.00% 0 0.47% 0 0.05% 0 2.68% 2 14.08%
> 40.00% 0 0.60% 0 0.50% 0 1.22% 0 11.58%
> 55.56% 2 4.25% 5 5.97% 0 2.51% 0 7.70%
> 55.56% 0 1.89% 0 0.04% 0 1.71% 6 8.06%
> 55.56% 0 0.50% 0 0.47% 0 1.82% 5 6.94%
> 75.00% 2 1.65% 1 0.46% 0 0.26% 56 3.59%
> 75.00% 0 1.68% 0 0.05% 0 0.49% 21 3.94%
> 75.00% 0 0.28% 0 0.23% 0 0.62% 4 4.41%
>
> Aside from the 2nd and 3rd tests schedutil is showing decreased
> performance across the board. The fifth test is particularly bad.
I guess you mean performance in terms of the overhead?
Thanks,
Rafael