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Subject: Re: [PATCH V3 0/4] cpufreq: cppc: Add support for frequency
 invariance
From:   Qian Cai <quic_qiancai@quicinc.com>
To:     Ionela Voinescu <ionela.voinescu@arm.com>
CC:     Vincent Guittot <vincent.guittot@linaro.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Rafael Wysocki <rjw@rjwysocki.net>,
        Ben Segall <bsegall@google.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Mel Gorman <mgorman@suse.de>,
        Peter Zijlstra <peterz@infradead.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Sudeep Holla <sudeep.holla@arm.com>,
        Will Deacon <will@kernel.org>,
        "open list:THERMAL" <linux-pm@vger.kernel.org>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
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Message-ID: <9096bdb2-2a38-6ba3-0315-f6e9bd5a4c0e@quicinc.com>
Date:   Sat, 26 Jun 2021 09:41:27 -0400
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On 6/25/2021 10:29 PM, 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. 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

Another date point is that set ACPI_CPPC_CPUFREQ_FIE=n fixed the issue that any CPU could run below the lowest freq.

schedutil:
# cat /sys/devices/system/cpu/*/cpufreq/cpuinfo_cur_freq | sort | uniq  -c
     80 1000000
     78 1400000
      1 2010000
      1 2800000

userspace:
# cat /sys/devices/system/cpu/*/cpufreq/cpuinfo_cur_freq | sort | uniq  -c
    158 1000000
      2 2000000