linux-kernel - RE: [PATCH v7 1/6] cpufreq:amd-pstate: fix the nominal freq value set

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Date: Thu, 14 Mar 2024 10:05:42 +0000
From: "Yuan, Perry" <Perry.Yuan@....com>
To: "Shenoy, Gautham Ranjal" <gautham.shenoy@....com>
CC: "rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>, "Limonciello,
 Mario" <Mario.Limonciello@....com>, "viresh.kumar@...aro.org"
	<viresh.kumar@...aro.org>, "Huang, Ray" <Ray.Huang@....com>, "Petkov,
 Borislav" <Borislav.Petkov@....com>, "Deucher, Alexander"
	<Alexander.Deucher@....com>, "Huang, Shimmer" <Shimmer.Huang@....com>, "Du,
 Xiaojian" <Xiaojian.Du@....com>, "Meng, Li (Jassmine)" <Li.Meng@....com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v7 1/6] cpufreq:amd-pstate: fix the nominal freq value set

[AMD Official Use Only - General]

> -----Original Message-----
> From: Shenoy, Gautham Ranjal <gautham.shenoy@....com>
> Sent: Thursday, March 14, 2024 5:32 PM
> To: Yuan, Perry <Perry.Yuan@....com>
> Cc: rafael.j.wysocki@...el.com; Limonciello, Mario
> <Mario.Limonciello@....com>; viresh.kumar@...aro.org; Huang, Ray
> <Ray.Huang@....com>; Petkov, Borislav <Borislav.Petkov@....com>; Deucher,
> Alexander <Alexander.Deucher@....com>; Huang, Shimmer
> <Shimmer.Huang@....com>; Du, Xiaojian <Xiaojian.Du@....com>; Meng, Li
> (Jassmine) <Li.Meng@....com>; linux-pm@...r.kernel.org; linux-
> kernel@...r.kernel.org
> Subject: Re: [PATCH v7 1/6] cpufreq:amd-pstate: fix the nominal freq value set
>
> Hello Perry,
>
> On Thu, Mar 14, 2024 at 11:39:20AM +0530, Yuan, Perry wrote:
> > [AMD Official Use Only - General]
> >
> >  Hi Gautham
> >
> > > -----Original Message-----
> > > From: Shenoy, Gautham Ranjal <gautham.shenoy@....com>
> > > Sent: Thursday, March 14, 2024 1:49 PM
> > > To: Yuan, Perry <Perry.Yuan@....com>
> > > Cc: rafael.j.wysocki@...el.com; Limonciello, Mario
> > > <Mario.Limonciello@....com>; viresh.kumar@...aro.org; Huang, Ray
> > > <Ray.Huang@....com>; Petkov, Borislav <Borislav.Petkov@....com>;
> > > Deucher, Alexander <Alexander.Deucher@....com>; Huang, Shimmer
> > > <Shimmer.Huang@....com>; Du, Xiaojian <Xiaojian.Du@....com>; Meng,
> > > Li (Jassmine) <Li.Meng@....com>; linux-pm@...r.kernel.org; linux-
> > > kernel@...r.kernel.org
> > > Subject: Re: [PATCH v7 1/6] cpufreq:amd-pstate: fix the nominal freq
> > > value set
> > >
> > > Hello Perry,
> > >
> > > On Wed, Mar 13, 2024 at 05:59:13PM +0800, Perry Yuan wrote:
> > > > Address an untested error where the nominal_freq was returned in
> > > > KHz instead of the correct MHz units, this oversight led to a
> > > > wrong nominal_freq set and resued, it will cause the max frequency
> > > > of core to be initialized with a wrong frequency value.
>
> What is still not clear from this commit log or the rest of the patch is, which part
> of the kernel code expects nominal_freq to be in MHz, when all the other freqs in
> cpudata are in KHz units.
>
> If nominal_freq is in KHz as it is currently, how does it cause the max frequency to
> be initialized to the wrong value ? Could you please elaborate this ?

OK,  here is the story.
Actually, the original capability values are Mhz like below, so the driver need to initialize the nominal_freq
as the as-it-is value, then pstate driver will calculate the max frequency as needed.

feedback_ctrs:ref:103751311076 del:87445442175
highest_perf:255
lowest_freq:400
lowest_nonlinear_perf:124
lowest_perf:30
nominal_freq:2801
nominal_perf:204
reference_perf:204
wraparound_time:18446744073709551615

The previous driver did not use the READ_ONCE(cpudata-> nominal_freq) at all.
We initialize all the freq and perf values in the init functions like you suggested in the other patchset.
 if driver still use Khz, below code will have problem.

        nominal_freq = READ_ONCE(cpudata-> nominal_freq);
        lowest_nonlinear_freq = nominal_freq * lowest_nonlinear_ratio >> SCHED_CAPACITY_SHIFT;

        /* Switch to khz */
        return lowest_nonlinear_freq * 1000;


Now we can read READ_ONCE(cpudata-> nominal_freq) without reading the CPPC ACPI again.
The nominal_freq must be in MHz as it is.

Perry.

>
> > >
> > > As I had mentioned in my review comment to v6 [1],
> > > cpudata->max_freq,
> > > cpudata->min_freq, cpudata->lowest_non_linear_freq are all in
> > > khz. With this patch, cpudata->nominal_freq will be in mhz.
> > >
> > > As Dhananjay confirmed [2], this patch breaks the reporting in
> > > /sys/devices/system/cpu/cpufreq/policyX/*_freq as some of them will
> > > be reported in mhz while some others in khz which breaks the
> > > expectation that all these sysfs values should be reported in khz.
> > >
> > > [cpufreq]# grep . *freq
> > > amd_pstate_lowest_nonlinear_freq:1804000   <----- in khz
> > > amd_pstate_max_freq:3514000                <----- in khz
> > > cpuinfo_max_freq:2151                      <----- in mhz
> > > cpuinfo_min_freq:400000                    <----- in khz
> > > scaling_cur_freq:2151                      <----- in mhz
> > > scaling_max_freq:2151                      <----- in mhz
> > > scaling_min_freq:2151                      <----- in mhz
> > > [cpufreq]# pwd
> > > /sys/devices/system/cpu/cpu0/cpufreq
> > >
> > > What am I missing ?
> >
> > https://lore.kernel.org/lkml/42a36c7f788e0fb77d4be7575aab9c937e1773de.
> > 1710322310.git.perry.yuan@....com/
> > Changes from v3:
> > * fix the max frequency value to be KHz when cpb boost
> > disabled(Gautham R. Shenoy)
>
> This CPB boost change assumes that cpudata->nominal_freq is in Mhz which is
> not the case until this patch. So is the CPB patchset dependent on this patch ?
>
> --
> Thanks and Regards
> gautham.
>
> >
> > The previous problem has been resolved by the new patchset of  cpb
> > boost support
> >
> > +       if (on)
> > +               policy->cpuinfo.max_freq = cpudata->max_freq;
> > +       else
> > +               policy->cpuinfo.max_freq = cpudata->nominal_freq *
> > + 1000;
> >
> >
> > The frequency values of cpuinfo are correct on my system.
> >
> > amd_pstate_lowest_nonlinear_freq:1701000
> > amd_pstate_max_freq:3501000
> > cpuinfo_max_freq:3501000
> > cpuinfo_min_freq:400000
> > scaling_cur_freq:400000
> > scaling_max_freq:3501000
> > scaling_min_freq:400000
> >
> > Perry.
> >
> > >
> > > [1] https://lore.kernel.org/lkml/ZcRvoYZKdUEjBUHp@BLR-
> > > 5CG11610CF.amd.com/)
> > > [2] https://lore.kernel.org/lkml/1aecf2fc-2ea4-46ec-aaf2-
> > > 0dbbb11b5f8b@....com/
> > >
> > > >
> > > > Cc: stable@...r.kernel.org
> > > > Fixes: ec437d71db7 ("cpufreq: amd-pstate: Introduce a new AMD
> > > > P-State driver to support future processors")
> > > > Reviewed-by: Mario Limonciello <mario.limonciello@....com>
> > > > Signed-off-by: Perry Yuan <perry.yuan@....com>
> > >
> > > --
> > > Thanks and Regards
> > > gautham.
> > >
> > >
> > > > ---
> > > >  drivers/cpufreq/amd-pstate.c | 3 +--
> > > >  1 file changed, 1 insertion(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/cpufreq/amd-pstate.c
> > > > b/drivers/cpufreq/amd-pstate.c index 2015c9fcc3c9..3faa895b77b7
> > > 100644
> > > > --- a/drivers/cpufreq/amd-pstate.c
> > > > +++ b/drivers/cpufreq/amd-pstate.c
> > > > @@ -647,8 +647,7 @@ static int amd_get_nominal_freq(struct
> > > amd_cpudata *cpudata)
> > > >     if (ret)
> > > >             return ret;
> > > >
> > > > -   /* Switch to khz */
> > > > -   return cppc_perf.nominal_freq * 1000;
> > > > +   return cppc_perf.nominal_freq;
> > > >  }
> > > >
> > > >  static int amd_get_lowest_nonlinear_freq(struct amd_cpudata
> > > > *cpudata)
> > > > --
> > > > 2.34.1
> > > >