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

[Rafael J. Wysocki]

On Fri, Mar 6, 2020 at 4:29 AM Huang, Ying <ying.huang@xxxxxxxxx> wrote:
>
> Hi, Rafael,
>
> "Rafael J. Wysocki" <rafael@xxxxxxxxxx> writes:
>
> > On Thu, Mar 5, 2020 at 9:18 AM Rong Chen <rong.a.chen@xxxxxxxxx> 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.