linux-kernel - Re: [PATCH] cpufreq: schedutil: Optimize operations with single max CPU capacity

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Date:   Tue, 6 Dec 2022 12:00:07 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        rafael@...nel.org, dietmar.eggemann@....com,
        vincent.guittot@...aro.org, saravanak@...gle.com,
        wusamuel@...gle.com, isaacmanjarres@...gle.com,
        kernel-team@...roid.com, juri.lelli@...hat.com,
        peterz@...radead.org, mingo@...hat.com, rostedt@...dmis.org,
        bsegall@...gle.com, mgorman@...e.de
Subject: Re: [PATCH] cpufreq: schedutil: Optimize operations with single max
 CPU capacity

On Tue, Dec 6, 2022 at 11:30 AM Lukasz Luba <lukasz.luba@....com> wrote:
>
>
>
> On 12/6/22 10:16, Viresh Kumar wrote:
> > On 06-12-22, 10:10, Lukasz Luba wrote:
> >> The max CPU capacity is the same for all CPUs sharing frequency domain
> >> and thus 'policy' object. There is a way to avoid heavy operations
> >> in a loop for each CPU by leveraging this knowledge. Thus, simplify
> >> the looping code in the sugov_next_freq_shared() and drop heavy
> >> multiplications. Instead, use simple max() to get the highest utilization
> >> from these CPUs. This is useful for platforms with many (4 or 6) little
> >> CPUs.
> >>
> >> The max CPU capacity must be fetched every time we are called, due to
> >> difficulties during the policy setup, where we are not able to get the
> >> normalized CPU capacity at the right time.
> >>
> >> The stored value in sugov_policy::max is also than used in
> >> sugov_iowait_apply() to calculate the right boost. Thus, that field is
> >> useful to have in that sugov_policy struct.
> >>
> >> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
> >
> > Can you please divide this into two patches, one for just moving max
> > and one for looping optimization ? Else we may end up reverting
> > everything once again.
> >
>
> OK, I can do that. Thanks for having a look!

Also, please note that this material is unlikely to go into 6.2, so
I'd prefer going back to it after 6.2-rc1 is out.