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

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Date:   Thu, 24 Jun 2021 11:17:55 -0400
From:   Qian Cai <quic_qiancai@...cinc.com>
To:     Ionela Voinescu <ionela.voinescu@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>
CC:     Viresh Kumar <viresh.kumar@...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 6/24/2021 6:48 AM, Ionela Voinescu wrote:
> Not if the counters are implemented properly. The kernel considers that
> both reference and delivered performance counters should stop or reset
> during idle. The kernel would not account for idle itself.
> 
> If the reference performance counter does not stop during idle, while
> the core performance counter (delivered) does stop, the behavior above
> should be seen very often.
> 
> Qian, do you see these small delivered performance values often or
> seldom?

Ionela, so I managed to upgrade the kernel on the system to today's linux-next which suppose to include this series. The delivered perf is now 280. However, scaling_min_freq (200 MHz) is not equal to lowest_perf (100).

scaling_driver: acpi_cppc
scaling_governor: schedutil

Is that normal because lowest_nonlinear_perf is 200? 

Also, on this pretty idle system, 158 of 160 CPUs are always running in max freq (280 MHz). The other 2 are running in 243 and 213 MHz according to scaling_cur_freq. Apparently, "schedutil" does not work proper on this system. I am going to try other governors to narrow down the issue a bit.

FYI, here is the acpi_cppc registers reading:

/sys/devices/system/cpu/cpu0/acpi_cppc/feedback_ctrs
ref:160705801 del:449594095
/sys/devices/system/cpu/cpu0/acpi_cppc/highest_perf
300
/sys/devices/system/cpu/cpu0/acpi_cppc/lowest_freq
1000
/sys/devices/system/cpu/cpu0/acpi_cppc/lowest_nonlinear_perf
200
/sys/devices/system/cpu/cpu0/acpi_cppc/lowest_perf
100
/sys/devices/system/cpu/cpu0/acpi_cppc/nominal_freq
2800
/sys/devices/system/cpu/cpu0/acpi_cppc/nominal_perf
280
/sys/devices/system/cpu/cpu0/acpi_cppc/reference_perf
100
/sys/devices/system/cpu/cpu0/acpi_cppc/wraparound_time
18446744073709551615