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

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Date:   Fri, 25 Jun 2021 22:29:26 -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 10:37 AM, Ionela Voinescu wrote:
> Quick questions for you:
> 
> 1. When you say you tried a 5.4 kernel, did you try it with these
> patches backported? They also have some dependencies with the recent
> changes in the arch topology driver and cpufreq so they would not be
> straight forward to backport.
> 
> If the 5.4 kernel you tried did not have these patches, it might be best
> to try next/master that has these patches, but with
> CONFIG_ACPI_CPPC_CPUFREQ_FIE=n, just to eliminate the possibility that
> an incorrect frequency scale factor here would affect utilization that
> would then affect the schedutil frequency selection. I would not expect
> this behavior even if the scale factor was wrong, but it would be good
> to rule out.
> 
> 2. Is your platform booting with all CPUs? Are any hotplug operations
> done in your scenario?

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. 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). 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