linux-kernel - Re: [PATCH V3 0/4] cpufreq: cppc: Add support for frequency invariance

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Date:   Thu, 24 Jun 2021 11:49:53 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Qian Cai <quic_qiancai@...cinc.com>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Ionela Voinescu <ionela.voinescu@....com>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Mel Gorman <mgorman@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Will Deacon <will@...nel.org>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH V3 0/4] cpufreq: cppc: Add support for frequency invariance

On Thu, 24 Jun 2021 at 04:54, Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 23-06-21, 08:57, Qian Cai wrote:
> > Viresh, I am afraid I don't feel comfortable yet. I have a few new tests in
> > development, and will provide an update once ready.
>
> Oh sure, np.
>
> > Also, I noticed the delivered perf is even smaller than lowest_perf (100).
>
> > # cat /sys/devices/system/cpu/cpu8/acpi_cppc/feedback_ctrs
> >  ref:103377547901 del:54540736873
> > # cat /sys/devices/system/cpu/cpu8/acpi_cppc/feedback_ctrs
> >  ref:103379170101 del:54541599117
> >
> > 100 * (54541599117 - 54540736873) / (103379170101 - 103377547901) = 53

I'm not sure that I understand your point. The formula above says that
cpu8 run @ 53% of nominal performance

> >
> > My understanding is that the delivered perf should fail into the range between
> > lowest_perf and highest_perf. Is that assumption correct? This happens on
> > 5.4-based kernel, so I am in process running your series on that system to see
> > if there is any differences. In any case, if it is a bug it is pre-existing,
> > but I'd like to understand a bit better in that front first.
>
> Vincent:
>
> Can that happen because of CPU idle ?
>
> --
> viresh