Re: [PATCH] cpufreq: schedutil: Don't use the limits_changed flag any more

[Yue Hu]

On Mon, 15 Feb 2021 12:00:08 +0530
Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:

> On 14-02-21, 11:44, Yue Hu wrote:
> > On Fri, 12 Feb 2021 17:14:03 +0100
> > "Rafael J. Wysocki" <rafael@xxxxxxxxxx> wrote:  
> > > This may be running in parallel with sugov_update_next_freq() on a
> > > different CPU, so the latter may clear need_freq_update right
> > > after it has been set here unless I'm overlooking something.  
> > 
> > Whether this logic is also happening for limits_changed in
> > sugo_should_update_freq() or not?  
> 
> It is but it shouldn't have any side effects as we calculate the next
> frequency after cleaning the limits_changed flag. Your patch would
> have been fine, but it is not anymore because of commit 23a881852f3e
> ("cpufreq: schedutil: Don't skip freq update if need_freq_update is
> set").
> 
> It made a considerable change after which your patch adds a bug. With
> 23a881852f3e, need_freq_update is updated/cleared after the next
> frequency is calculated, while earlier it was cleared before it. And
> so even with the race condition taking place, there were no issues.
> 

Okay, clear.