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 15:02:11 +0530
From: "Gautham R. Shenoy" <gautham.shenoy@....com>
To: "Yuan, Perry" <Perry.Yuan@....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

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 ?

> >
> > 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@amd.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
> > >