linux-kernel - Re: [PATCH] cpufreq: schedutil: Don't consider freq reduction to busy CPU if need_freq

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Date:   Fri, 19 Feb 2021 13:12:49 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Yue Hu <zbestahu@...il.com>
Cc:     rjw@...ysocki.net, mingo@...hat.com, peterz@...radead.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        huyue2@...ong.com, zbestahu@....com
Subject: Re: [PATCH] cpufreq: schedutil: Don't consider freq reduction to
 busy CPU if need_freq_update is set

On 19-02-21, 14:41, Yue Hu wrote:
> On Fri, 19 Feb 2021 09:39:33 +0530
> Viresh Kumar <viresh.kumar@...aro.org> wrote:
> 
> > On 19-02-21, 11:38, Yue Hu wrote:
> > > There's a possibility: we will use the previous freq to update if
> > > next_f is reduced for busy CPU if need_freq_update is set in
> > > sugov_update_next_freq().  
> > 
> > Right.
> > 
> > > This possibility would happen now? And this
> > > update is what we want if it happens?  
> > 
> > This is exactly what we want here, don't reduce speed for busy CPU,
> 
> I understand it should not skip this update but set the same freq as
> previous one again for the special case if need_freq_update is set. Am
> i rt?

The special check, about not reducing freq if CPU had been busy
recently, doesn't have anything to do with need_freq_update.

Though previously we added the need_freq_update check there to make
sure we account for any recent policy min/max change and don't skip
freq update anymore. That won't happen anymore and so we don't need
any check here related to need_freq_update.

If you still have doubt, please explain your concern in detail with an
example as I am failing to understand it.

-- 
viresh