Re: [PATCH v3 05/14 RESEND] xenpm: Change get-cpufreq-para output for internal

[Jason Andryuk <jandryuk@xxxxxxxxx>]

On Thu, May 4, 2023 at 10:35 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>
> On 01.05.2023 21:30, Jason Andryuk wrote:
> > When using HWP, some of the returned data is not applicable.  In that
> > case, we should just omit it to avoid confusing the user.  So switch to
> > printing the base and turbo frequencies since those are relevant to HWP.
> > Similarly, stop printing the CPU frequencies since those do not apply.
>
> It vaguely feels like I have asked this before: Can you point me at a
> place in the SDM where it is said that CPUID 0x16's "Maximum Frequency"
> is the turbo frequency? Without such a reference I feel a little uneasy
> with ...

I don't have a reference, but I found it empirically to match the
"turbo" frequency.

For an Intel® Core™ i7-10810U,
https://ark.intel.com/content/www/us/en/ark/products/201888/intel-core-i710810u-processor-12m-cache-up-to-4-90-ghz.html

Max Turbo Frequency 4.90 GHz

# xenpm get-cpufreq-para
cpu id               : 0
affected_cpus        : 0
cpuinfo frequency    : base [1600000] turbo [4900000]

Turbo has to be enabled to reach (close to) that frequency.

>From my cover letter:
This is for a 10th gen 6-core 1600 MHz base 4900 MHZ max cpu.  In the
default balance mode, Turbo Boost doesn't exceed 4GHz.  Tweaking the
energy_perf preference with `xenpm set-cpufreq-hwp balance ene:64`,
I've seen the CPU hit 4.7GHz before throttling down and bouncing around
between 4.3 and 4.5 GHz.  Curiously the other cores read ~4GHz when
turbo boost takes affect.  This was done after pinning all dom0 cores,
and using taskset to pin to vCPU/pCPU 11 and running a bash tightloop.

> > @@ -720,10 +721,15 @@ static void print_cpufreq_para(int cpuid, struct 
> > xc_get_cpufreq_para *p_cpufreq)
> >          printf(" %d", p_cpufreq->affected_cpus[i]);
> >      printf("\n");
> >
> > -    printf("cpuinfo frequency    : max [%u] min [%u] cur [%u]\n",
> > -           p_cpufreq->cpuinfo_max_freq,
> > -           p_cpufreq->cpuinfo_min_freq,
> > -           p_cpufreq->cpuinfo_cur_freq);
> > +    if ( internal )
> > +        printf("cpuinfo frequency    : base [%u] turbo [%u]\n",
> > +               p_cpufreq->cpuinfo_min_freq,
> > +               p_cpufreq->cpuinfo_max_freq);
>
> ... calling it "turbo" (and not "max") here.

I'm fine with "max".  I think I went with turbo since it's a value you
cannot sustain but can only hit in short bursts.

Regards,
Jason