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

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Date:   Tue, 5 Sep 2023 20:30:34 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Keyon Jie <yang.jie@...ux.intel.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        "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 Tue, Sep 5, 2023 at 8:17 PM Keyon Jie <yang.jie@...ux.intel.com> wrote:
>
>
>
> On 8/29/23 01:57, Greg KH wrote:
> > 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 When the CPU frequency is outdated arch_freq_get_on_cpu()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.
>
> Thank you Greg.
>
> Hi Rafael,
>
> As the issue happens from the 5.18 onward kernels, we need the fix to be
> picked for stable kernels after that, could you please help to add "Cc:
> stable@...r.kernel.org" in the sign-off area when you send it to the
> mainline?

It's already merged, as commit d51847acb018 ("cpufreq: intel_pstate:
set stale CPU frequency to minimum").

Please feel free to send an inclusion request for it to stable@...r.kernel.org

Thanks!