linux-kernel - Re: [PATCH 1/2] cpufreq: Fix re-boost issue after hotplugging a cpu

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Message-ID: <CAJZ5v0h9zb=_HTR-nraCZj18YcOSfkMm7WVZ4ePsziOzpV0ndg@mail.gmail.com>
Date: Wed, 15 Jan 2025 13:50:45 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Viresh Kumar <viresh.kumar@...aro.org>
Cc: Lifeng Zheng <zhenglifeng1@...wei.com>, rafael@...nel.org, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linuxarm@...wei.com, 
	jonathan.cameron@...wei.com, zhanjie9@...ilicon.com, lihuisong@...wei.com, 
	fanghao11@...wei.com
Subject: Re: [PATCH 1/2] cpufreq: Fix re-boost issue after hotplugging a cpu

On Wed, Jan 15, 2025 at 12:18 PM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 15-01-25, 18:01, Lifeng Zheng wrote:
> > It turns out that cpuX will stay on the base frequency after performing
> > these operations:
> >
> > 1. boost all cpus: echo 1 > /sys/devices/system/cpu/cpufreq/boost
> >
> > 2. offline the cpu: echo 0 > /sys/devices/system/cpu/cpuX/online
> >
> > 3. deboost all cpus: echo 0 > /sys/devices/system/cpu/cpufreq/boost
> >
> > 4. online the cpu: echo 1 > /sys/devices/system/cpu/cpuX/online
> >
> > 5. boost all cpus again: echo 1 > /sys/devices/system/cpu/cpufreq/boost
> >
> > This is because max_freq_req of the policy is not updated during the
> > online process, and the value of max_freq_req before the last offline is
> > retained. When the CPU is boosted again, freq_qos_update_request() will
> > do nothing because the old value is the same as the new one. This causes
> > the CPU stay on the base frequency. Update max_freq_req (and
> > min_freq_req of course) in cpufreq_online() will solve this problem.
> >
> > Signed-off-by: Lifeng Zheng <zhenglifeng1@...wei.com>
> > ---
> >  drivers/cpufreq/cpufreq.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index 1a4cae54a01b..03ae879d50b9 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -1475,6 +1475,13 @@ static int cpufreq_online(unsigned int cpu)
> >
> >               blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
> >                               CPUFREQ_CREATE_POLICY, policy);
> > +     } else {
> > +             ret = freq_qos_update_request(policy->min_freq_req, policy->min);
>
> This may not be required, as min-freq-req is never updated.

It gets updated via scaling_min_freq AFAICS.  Doesn't this matter?

> > +             if (ret < 0)
> > +                     goto out_destroy_policy;
> > +             ret = freq_qos_update_request(policy->max_freq_req, policy->max);
> > +             if (ret < 0)
> > +                     goto out_destroy_policy;
> >       }
> >
> >       if (cpufreq_driver->get && has_target()) {
> > --