linux-kernel - Re: [PATCH v2] cpufreq/amd-pstate: Write CPPC enable bit per-socket

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Date:   Fri, 16 Jun 2023 19:31:38 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Huang Rui <ray.huang@....com>, "Karny, Wyes" <wyes.karny@....com>
Cc:     "rafael@...nel.org" <rafael@...nel.org>,
        "viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
        "Limonciello, Mario" <Mario.Limonciello@....com>,
        "Yuan, Perry" <Perry.Yuan@....com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Shenoy, Gautham Ranjal" <gautham.shenoy@....com>
Subject: Re: [PATCH v2] cpufreq/amd-pstate: Write CPPC enable bit per-socket

On Fri, Jun 16, 2023 at 9:03 AM Huang Rui <ray.huang@....com> wrote:
>
> On Tue, May 30, 2023 at 09:13:48PM +0800, Karny, Wyes wrote:
> > Currently amd_pstate sets CPPC enable bit in MSR_AMD_CPPC_ENABLE only
> > for the CPU where the module_init happened. But MSR_AMD_CPPC_ENABLE is
> > per-socket. This causes CPPC enable bit to set for only one socket for
> > servers with more than one physical packages. To fix this write
> > MSR_AMD_CPPC_ENABLE per-socket.
> >
> > Also, handle duplicate calls for cppc_enable, because it's called from
> > per-policy/per-core callbacks and can result in duplicate MSR writes.
> >
> > Before the fix:
> > amd@amd:~$ sudo rdmsr -a 0xc00102b1 | uniq --count
> >       192 0
> >     192 1
> >
> > After the fix:
> > amd@amd:~$ sudo rdmsr -a 0xc00102b1 | uniq --count
> >     384 1
> >
> > Suggested-by: Gautham R. Shenoy <gautham.shenoy@....com>
> > Signed-off-by: Wyes Karny <wyes.karny@....com>
> > ---
> > v1 -> v2:
> > - Made CPPC enable read/write per-socket
> >
> >  drivers/cpufreq/amd-pstate.c | 28 +++++++++++++++++++++++++++-
> >  1 file changed, 27 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> > index 5a3d4aa0f45a..45b9e359f638 100644
> > --- a/drivers/cpufreq/amd-pstate.c
> > +++ b/drivers/cpufreq/amd-pstate.c
> > @@ -63,6 +63,7 @@ static struct cpufreq_driver *current_pstate_driver;
> >  static struct cpufreq_driver amd_pstate_driver;
> >  static struct cpufreq_driver amd_pstate_epp_driver;
> >  static int cppc_state = AMD_PSTATE_DISABLE;
> > +static bool cppc_enabled;
> >
> >  /*
> >   * AMD Energy Preference Performance (EPP)
> > @@ -228,7 +229,28 @@ static int amd_pstate_set_energy_pref_index(struct amd_cpudata *cpudata,
> >
> >  static inline int pstate_enable(bool enable)
> >  {
> > -     return wrmsrl_safe(MSR_AMD_CPPC_ENABLE, enable);
> > +     int ret, cpu;
> > +     unsigned long logical_proc_id_mask = 0;
> > +
> > +     if (enable == cppc_enabled)
> > +             return 0;
> > +
> > +     for_each_present_cpu(cpu) {
> > +             unsigned long logical_id = topology_logical_die_id(cpu);
> > +
> > +             if (test_bit(logical_id, &logical_proc_id_mask))
> > +                     continue;
> > +
> > +             set_bit(logical_id, &logical_proc_id_mask);
> > +
> > +             ret = wrmsrl_safe_on_cpu(cpu, MSR_AMD_CPPC_ENABLE,
> > +                             enable);
>
> Thanks Wyes, that makes a lot more sense to me. The MSR is per package on
> design. We should only write once per package.
>
> Patch is
>
> Acked-by: Huang Rui <ray.huang@....com>

Applied as 6.5 material, thanks!