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

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Date:   Tue, 29 Jun 2021 10:22:36 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Qian Cai <quic_qiancai@...cinc.com>
Cc:     Ionela Voinescu <ionela.voinescu@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        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 25-06-21, 22:29, Qian Cai wrote:
> Ionela, I found that set ACPI_PROCESSOR=y instead of
> ACPI_PROCESSOR=m will fix the previous mentioned issues here (any
> explanations of that?) even though the scaling down is not perfect.

Not sure how this affects it.

> Now, we have the following on this idle system:
> 
> # cat /sys/devices/system/cpu/*/cpufreq/cpuinfo_cur_freq | sort | uniq  -c
>  	79 1000000
>   	1 1160000
>  	73 1400000
>   	1 2000000
>   	4 2010000
>   	1 2800000
>   	1 860000
> 
> Even if I rerun a few times, there could still have a few CPUs
> running lower than lowest_perf (1GHz).

(Please wrap your lines at 80 columns, it makes it harder to read
otherwise).

I think only the counters stopping on idle can get us that.

> Also, even though I set all CPUs to use "userspace" governor and set
> freq to the lowest. A few CPUs keep changing at will.
> 
> # cat /sys/devices/system/cpu/*/cpufreq/cpuinfo_cur_freq | sort | uniq  -c
> 	156 1000000
>   	3 2000000
>   	1 760000

I think this is expected since the hardware is in control of frequency
here. The software can only request it to run at X frequency, the
hardware may choose to do something else nevertheless.

-- 
viresh