Re: Ask for help on governor

[Viresh Kumar <viresh.kumar@linaro.org>]

On 12-12-17, 19:10, Doug Smythies wrote:
> Thanks for the suggestion. It was so very close, the problem commit is the very
> next one, aa7519af450d.
> 
> Bisect result:
> 
> aa7519af450d3c62a057aece24877c34562fa25a is the first bad commit
> commit aa7519af450d3c62a057aece24877c34562fa25a
> Author: Viresh Kumar <viresh.kumar@linaro.org>
> Date:   Wed Jul 19 15:42:42 2017 +0530
> 
>     cpufreq: Use transition_delay_us for legacy governors as well
> 
>     The policy->transition_delay_us field is used only by the schedutil
>     governor currently, and this field describes how fast the driver wants
>     the cpufreq governor to change CPUs frequency. It should rather be a
>     common thing across all governors, as it doesn't have any schedutil
>     dependency here.
> 
>     Create a new helper cpufreq_policy_transition_delay_us() to get the
>     transition delay across all governors.
> 
>     Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
>     Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

What has changed for intel-pstate after this patch ?

sampling_rate for conservative and ondemand is 500 us now, which was 20000 us
earlier. So we reevaluate load very frequently now, but in case load isn't over
80% then we wouldn't increase the frequency.

@Doug/Andy: Can you please try following:

- Checkout 4.14 or mainline (the broken kernels).
- Set governor to conservative.
- Monitor /sys/devices/system/cpu/cpufreq/policy*/stats/total_trans (to check if
  frequency is getting changed or not).
- Run some dummy load, I did this:

  perf bench sched messaging --pipe --thread --group 8 

This should result in frequency updates, so its not that we aren't changing
frequency at all now with conservative.

Then do this:

echo 20000 > /sys/devices/system/cpu/cpufreq/conservative/sampling_rate

and this should take you back to the original behavior which was there pre-4.14.

@Andy: What's your hardware and cpufreq driver ? intel-pstate? As I am not sure
why things will change for any other driver than intel-pstate.

I am not really sure what's the right way forward here now.

-- 
viresh