Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Wed, 24 Feb 2021 13:46:11 +0100 | Subject | Re: [PATCH] cpufreq: schedutil: Don't consider freq reduction to busy CPU if need_freq_update is set |
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On Wed, Feb 24, 2021 at 3:24 AM Yue Hu <zbestahu@gmail.com> wrote: > > On Mon, 22 Feb 2021 15:30:34 +0100 > "Rafael J. Wysocki" <rafael@kernel.org> wrote: > > > On Mon, Feb 22, 2021 at 2:57 PM Yue Hu <zbestahu@163.com> wrote: > > > > > > On Mon, 22 Feb 2021 11:00:14 +0530 > > > Viresh Kumar <viresh.kumar@linaro.org> wrote: > > > > > > > On 19-02-21, 19:45, Yue Hu wrote: > > > > > We will set next_f to next_freq(previous freq) if next_f is > > > > > reduced for busy CPU. Then the next sugov_update_next_freq() will check > > > > > if next_freq matches next_f if need_freq_update is not set. > > > > > Obviously, we will do nothing for the case. And The related check to > > > > > fast_switch_enabled and raw_spin_{lock,unlock} operations are > > > > > unnecessary. > > > > > > > > Right, but we will still need sugov_update_next_freq() to have the > > > > same implementation regardless and so I am not sure if we should add > > > > > > Yes, sugov_update_next_freq() should be keeping current logic for corner case. > > > > > > > this change: > > > > > > > > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c > > > > index 41e498b0008a..7289e1adab73 100644 > > > > --- a/kernel/sched/cpufreq_schedutil.c > > > > +++ b/kernel/sched/cpufreq_schedutil.c > > > > @@ -362,6 +362,9 @@ static void sugov_update_single_freq(struct update_util_data *hook, u64 time, > > > > * recently, as the reduction is likely to be premature then. > > > > */ > > > > if (sugov_cpu_is_busy(sg_cpu) && next_f < sg_policy->next_freq) { > > > > + if (!sg_policy->need_freq_update) > > > > > > The initial purpose about code of `next_f = sg_policy->next_freq` here (for special CPU busy > > > case) should be skipping the freq update. > > > > > > Since commit 600f5badb78c ("cpufreq: schedutil: Don't skip freq update when limits change"), > > > we add the check to busy CPU for not skipping the update, we need to update the freq using > > > computed one because limits change. > > > > > > After commit 23a881852f3e ("cpufreq: schedutil: Don't skip freq update if need_freq_update > > > is set"), we removed the need_freq_update check(no issue of commit 600f5badb78c anymore?) > > > and introduce to always do an update in sugov_update_next_freq() if need_freq_update is set > > > even though current freq == sg_policy->next_freq because of corner case issue. But that is > > > conflict with original purpose of the freq skip code (next_f = sg_policy->next_freq) of > > > busy CPU. > > > > That's because we realized that it was not always a good idea to skip > > the update even if next_f == sg_policy->next_freq. > > > > That's why CPUFREQ_NEED_UPDATE_LIMITS has been introduced and the > > current flow is a result of subsequent code rearrangements. > > ok, care about unnecessary(should be) behaviors(fast_switch_enabled and raw_spin_{lock,unlock}) > if need_freq_update is unset? > > If we care, i will send another patch (which is different from above change for busy CPU).
Please send a patch and we'll see (this is how things go).
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