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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Thu, 5 Oct 2023 13:35:13 +0200
Message-ID: <CAJZ5v0j8T0KUjLzS=MCF1M33KMhf-EVrT1W5Tncr6wnOXUMgwQ@mail.gmail.com>
Subject: Re: [PATCH] cpufreq: schedutil: next_freq need update when
 cpufreq_limits changed
To:     Ingo Molnar <mingo@kernel.org>
Cc:     Xuewen Yan <xuewen.yan@unisoc.com>, rafael@kernel.org,
        viresh.kumar@linaro.org, mingo@redhat.com, peterz@infradead.org,
        vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
        bristot@redhat.com, vschneid@redhat.com, guohua.yan@unisoc.com,
        qyousef@layalina.io, linux-pm@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Thu, Oct 5, 2023 at 1:26 PM Ingo Molnar <mingo@kernel.org> wrote:
>
>
> * Xuewen Yan <xuewen.yan@unisoc.com> wrote:
>
> > When cpufreq's policy is single, there is a scenario that will
> > cause sg_policy's next_freq to be unable to update.
> >
> > When the cpu's util is always max, the cpufreq will be max,
> > and then if we change the policy's scaling_max_freq to be a
> > lower freq, indeed, the sg_policy's next_freq need change to
> > be the lower freq, however, because the cpu_is_busy, the next_freq
> > would keep the max_freq.
> >
> > For example:
> > The cpu7 is single cpu:
> >
> > unisoc:/sys/devices/system/cpu/cpufreq/policy7 # while true;do done&
> > [1] 4737
> > unisoc:/sys/devices/system/cpu/cpufreq/policy7 # taskset -p 80 4737
> > pid 4737's current affinity mask: ff
> > pid 4737's new affinity mask: 80
> > unisoc:/sys/devices/system/cpu/cpufreq/policy7 # cat scaling_max_freq
> > 2301000
> > unisoc:/sys/devices/system/cpu/cpufreq/policy7 # cat scaling_cur_freq
> > 2301000
> > unisoc:/sys/devices/system/cpu/cpufreq/policy7 # echo 2171000 > scaling_max_freq
> > unisoc:/sys/devices/system/cpu/cpufreq/policy7 # cat scaling_max_freq
> > 2171000
> >
> > At this time, the sg_policy's next_freq would keep 2301000.
> >
> > To prevent the case happen, add the judgment of the need_freq_update flag.
> >
> > Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com>
> > Co-developed-by: Guohua Yan <guohua.yan@unisoc.com>
> > Signed-off-by: Guohua Yan <guohua.yan@unisoc.com>
> > ---
> >  kernel/sched/cpufreq_schedutil.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> > index 4492608b7d7f..458d359f5991 100644
> > --- a/kernel/sched/cpufreq_schedutil.c
> > +++ b/kernel/sched/cpufreq_schedutil.c
> > @@ -350,7 +350,8 @@ static void sugov_update_single_freq(struct update_util_data *hook, u64 time,
> >        * Except when the rq is capped by uclamp_max.
> >        */
> >       if (!uclamp_rq_is_capped(cpu_rq(sg_cpu->cpu)) &&
> > -         sugov_cpu_is_busy(sg_cpu) && next_f < sg_policy->next_freq) {
> > +         sugov_cpu_is_busy(sg_cpu) && next_f < sg_policy->next_freq &&
> > +         !sg_policy->need_freq_update) {
> >               next_f = sg_policy->next_freq;
> >
> >               /* Restore cached freq as next_freq has changed */
>
> Just wondering about the status of this fix - is it pending in
> some tree, or should we apply it to the scheduler tree?

I have not queued it up yet, so it can be applied to the scheduler tree.

Thanks!