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

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Date:   Fri, 25 Jun 2021 09:31:58 -0400
From:   Qian Cai <quic_qiancai@...cinc.com>
To:     Ionela Voinescu <ionela.voinescu@....com>
CC:     Vincent Guittot <vincent.guittot@...aro.org>,
        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 6/25/2021 6:21 AM, Ionela Voinescu wrote:
>> scaling_driver: acpi_cppc
>                   ^^^^^^^^^
> I suppose you mean "cppc-cpufreq"?
> 
> "acpi_cppc" is not a scaling driver option.

Ionela, yes. Sorry about that.

> So your CPUs run at frequencies between 200MHz and 280MHz?

2000 to 2800 MHz.

> Based on your acpi_cppc information below I would have assumed 2GHz as
> lowest nonlinear and 2.8GHz as nominal. The reason for this is that
> according to the ACPI spec the frequency values in the _CPC objects are
> supposed to be in MHz, so 2800 MHz for nominal frequency would be
> 2.8GHz.
> 
> When you try more governors, make sure to check out the difference
> between scaling_cur_freq and cpuinfo_cur_freq at [2]. The first gives
> you the frequency that the governor (schedutil) is asking for, while the
> second is giving you the current frequency obtained from the counters.
> 
> So to check the actual frequency the cores are running at, please check
> cpuinfo_cur_freq.

The problem is that all CPUs are never scaling down. "cpuinfo_cur_freq" and "scaling_cur_freq" are always the 2800 MHz on all CPUs on this idle system. This looks like a regression somewhere as in 5.4-based kernel, I can see "cpuinfo_cur_freq" can go down to 2000 MHz in the same scenario. I'll bisect a bit unless you have better ideas?