Re: [LKP] Re: [cpufreq] 909c0e9cc1: fwq.fwq.med 210.0% improvement

["Huang\, Ying" <ying.huang@intel.com>]

"Rafael J. Wysocki" <rafael@kernel.org> writes:

> On Mon, Mar 9, 2020 at 2:17 AM Huang, Ying <ying.huang@intel.com> wrote:
>>
>> "Rafael J. Wysocki" <rafael@kernel.org> writes:
>>
>> > On Fri, Mar 6, 2020 at 4:29 AM Huang, Ying <ying.huang@intel.com> wrote:
>> >>
>> >> Hi, Rafael,
>> >>
>> >> "Rafael J. Wysocki" <rafael@kernel.org> writes:
>> >>
>> >> > On Thu, Mar 5, 2020 at 9:18 AM Rong Chen <rong.a.chen@intel.com> wrote:
>> >> >>
>> >> >>
>> >> >>
>> >> >> On 3/5/20 3:50 PM, Rafael J. Wysocki wrote:
>> >> >> > On 3/5/2020 2:35 AM, kernel test robot wrote:
>> >> >> >> Greeting,
>> >> >> >>
>> >> >> >> FYI, we noticed a 210.0% improvement of fwq.fwq.med due to commit:
>> >> >> >
>> >> >> > Well, that sounds impressive. :-)
>> >> >> >
>> >> >> >
>> >> >> >>
>> >> >> >> commit: 909c0e9cc11ba39fa5a660583b25c2431cf54deb ("cpufreq:
>> >> >> >> intel_pstate: Use passive mode by default without HWP")
>> >> >> >> https://git.kernel.org/cgit/linux/kernel/git/rafael/linux-pm.git
>> >> >> >> intel_pstate-passive
>> >> >> >>
>> >> >> >> in testcase: fwq
>> >> >> >> on test machine: 16 threads Intel(R) Xeon(R) CPU D-1541 @ 2.10GHz
>> >> >> >> with 48G memory
>> >> >> >> with following parameters:
>> >> >> >>
>> >> >> >>     nr_task: 100%
>> >> >> >>     samples: 100000ss
>> >> >> >>     iterations: 18x
>> >> >> >>     cpufreq_governor: powersave
>> >> >> >
>> >> >> > The governor should be schedutil, though, unless it is explicitly set
>> >> >> > to powersave in the test environment.
>> >> >> >
>> >> >> > Is that the case?
>> >> >> >
>> >> >> >
>> >> >>
>> >> >> Hi Rafael,
>> >> >>
>> >> >> Yes, we set to powersave for this test.
>> >> >
>> >> > I wonder why this is done?  Is there any particular technical reason
>> >> > for doing that?
>> >>
>> >> fwq is a noise benchmark to measure the hardware and software noise
>> >> level.  More information could be found in the following document.
>> >>
>> >> https://asc.llnl.gov/sequoia/benchmarks/FTQ_summary_v1.1.pdf
>> >>
>> >> In 0day, to measure the noise introduced by power management, we will
>> >> run fwq with the performance and powersave governors.  Do you think this
>> >> is reasonable?  Or we should use some other governors?
>> >
>> > I think that the schedutil governor should be tested too if present.
>> >
>> > Also note that for the intel_pstate driver "powersave" may mean
>> > different things depending on the current operation mode of the
>> > driver.  If scaling_driver is "intel_pstate", then "powersave" is the
>> > driver's built-in algorithm.  If scaling_driver is "intel_cpufreq",
>> > though, "powersave" means running at the minimum frequency all the
>> > time.
>>
>> Thanks for your guidance.  We will test schedutil governor in the future
>> too.
>>
>> As for powersave, should we stop testing it?
>
> You cannot stop testing it, because it is the default governor
> algorithm for intel_pstate working in the active mode.
>
>>  Or just pay attention to the possible issue you pointed out?
>
> Yes, please!
>
> Basically, I would recommend to test the following configurations by default:
>
> (1) scaling_driver = intel_pstate + scaling_governor = powersave
>
> (2) scaling_driver = intel_cpufreq + scaling_governor = schedutil
>
> The other ones are kind of less interesting.
>
> [Note that in order to switch over from intel_pstate to intel_cpufreq,
> you need to write "passive" into
> /sys/devices/system/cpu/intel_pstate/status and if that write fails,
> configuration (2) is not available and may be skipped.]
>
>> Should we add ondemand governor?
>
> Not necessarily, maybe as a reference only if you have spare cycles.

Got it!  Thanks a lot for your information!

Best Regards,
Huang, Ying

> Thanks!