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

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Date:   Thu, 24 Jun 2021 08:24:14 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Qian Cai <quic_qiancai@...cinc.com>
Cc:     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>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Will Deacon <will@...nel.org>, linux-pm@...r.kernel.org,
        linux-acpi@...r.kernel.org, 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 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
> 
> 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