On Mon, 22 Feb 2021 15:30:34 +0100 "Rafael J. Wysocki" <[email protected]> wrote:
> On Mon, Feb 22, 2021 at 2:57 PM Yue Hu <[email protected]> wrote: > > > > On Mon, 22 Feb 2021 11:00:14 +0530 > > Viresh Kumar <[email protected]> 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). Thank you.
