linux-kernel - Re: [PATCH v2] cpufreq: intel_pstate: set stale CPU frequency to minimum

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Date:   Tue, 29 Aug 2023 10:57:32 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Keyon Jie <yang.jie@...ux.intel.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Doug Smythies <dsmythies@...us.net>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <lenb@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] cpufreq: intel_pstate: set stale CPU frequency to
 minimum

On Mon, Aug 28, 2023 at 04:35:13PM -0700, Keyon Jie wrote:
> 
> 
> On 8/22/23 04:46, Rafael J. Wysocki wrote:
> > On Sun, Aug 20, 2023 at 10:46 PM Doug Smythies <dsmythies@...us.net> wrote:
> > > 
> > > The intel_pstate CPU frequency scaling driver does not
> > > use policy->cur and it is 0.
> > > When the CPU frequency is outdated arch_freq_get_on_cpu()
> > > will default to the nominal clock frequency when its call to
> > > cpufreq_quick_getpolicy_cur returns the never updated 0.
> > > Thus, the listed frequency might be outside of currently
> > > set limits. Some users are complaining about the high
> > > reported frequency, albeit stale, when their system is
> > > idle and/or it is above the reduced maximum they have set.
> > > 
> > > This patch will maintain policy_cur for the intel_pstate
> > > driver at the current minimum CPU frequency.
> > > 
> > > Reported-by: Yang Jie <yang.jie@...ux.intel.com>
> > > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217597
> > > Signed-off-by: Doug Smythies <dsmythies@...us.net>
> > > ---
> > > 
> > > v1 -> v2:
> > >     * v1 was a completely different approach, programming around
> > >       the issue rather than fixing it at the source.
> > >       reference:
> > >       https://patchwork.kernel.org/project/linux-pm/patch/006901d9be8c$f4439930$dccacb90$@telus.net/
> > >     * v2 does not fix an issue with the intel_cpufreq CPU scaling
> > >       driver (A.K.A. the intel_pstate driver in passive mode) and
> > >       the schedutil CPU frequency scaling governor when HWP is enabled
> > >       where limit changes are not reflected in the stale listed frequencies.
> > >       A fix for that will be some future patch.
> > > 
> > > ---
> > >   drivers/cpufreq/intel_pstate.c | 5 +++++
> > >   1 file changed, 5 insertions(+)
> > > 
> > > diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> > > index 8ca2bce4341a..08284dee583a 100644
> > > --- a/drivers/cpufreq/intel_pstate.c
> > > +++ b/drivers/cpufreq/intel_pstate.c
> > > @@ -2609,6 +2609,11 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy)
> > >                          intel_pstate_clear_update_util_hook(policy->cpu);
> > >                  intel_pstate_hwp_set(policy->cpu);
> > >          }
> > > +       /* policy current is never updated with the intel_pstate driver
> > > +        * but it is used as a stale frequency value. So, keep it within
> > > +        * limits.
> > > +        */
> > > +       policy->cur = policy->min;
> > > 
> > >          mutex_unlock(&intel_pstate_limits_lock);
> > > 
> > > --
> > 
> > Applied as 6.6 material, with some mailer-induced white space damage
> > fixed and the new comment adjusted to the kernel coding style.
> > 
> > Thanks!
> 
> Hi Doug and Rafael,
> 
> Thank you for making the fix happen.
> 
> Hi Greg,
> 
> Will this be picked to the stable linux-6.1.y and linux-6.4.y kernel, it
> could benefit to users there.

Sure, when it hits Linus's tree, please follow the instructions in:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to get it merged.

thanks,

greg k-h