linux-kernel - Re: [patch 00/10] x86/cpu: Consolidate APERF/MPERF code

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Message-ID: <87bkwwvkwa.ffs@tglx>
Date:   Tue, 19 Apr 2022 23:11:17 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Doug Smythies <dsmythies@...us.net>
Cc:     the arch/x86 maintainers <x86@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch 00/10] x86/cpu: Consolidate APERF/MPERF code

On Tue, Apr 19 2022 at 20:49, Rafael J. Wysocki wrote:
> On Tue, Apr 19, 2022 at 7:32 PM Doug Smythies <dsmythies@...us.net> wrote:
>> For intel_pstate (active), both HWP enabled or disabled, the behaviour
>> of scaling_cur_freq is inconsistent with prior to this patch set and other
>> scaling driver governor combinations.
>>
>> Note there is no issue with " grep MHz /proc/cpuinfo" for any
>> combination.
>>
>> Examples:
>>
>> No-HWP:
>>
>> active/powersave:
>> doug@s19:~/freq-scalers/trace$ grep . /sys/devices/system/cpu/cpu*/cpufreq/scaling_cur_freq
>> /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq:2300418
>> /sys/devices/system/cpu/cpu10/cpufreq/scaling_cur_freq:0
>> /sys/devices/system/cpu/cpu11/cpufreq/scaling_cur_freq:0
>> /sys/devices/system/cpu/cpu1/cpufreq/scaling_cur_freq:0
>> /sys/devices/system/cpu/cpu2/cpufreq/scaling_cur_freq:0
>> /sys/devices/system/cpu/cpu3/cpufreq/scaling_cur_freq:0
>> /sys/devices/system/cpu/cpu4/cpufreq/scaling_cur_freq:0
>> /sys/devices/system/cpu/cpu5/cpufreq/scaling_cur_freq:0
>> /sys/devices/system/cpu/cpu6/cpufreq/scaling_cur_freq:0
>> /sys/devices/system/cpu/cpu7/cpufreq/scaling_cur_freq:2300006
>> /sys/devices/system/cpu/cpu8/cpufreq/scaling_cur_freq:2300005
>> /sys/devices/system/cpu/cpu9/cpufreq/scaling_cur_freq:0
>
> That's because after the changes in this series scaling_cur_freq
> returns 0 if the given CPU is idle.

Which is sensible IMO as there is really no point in waking an idle CPU
just to read those MSRs, then wait 20ms wake it up again to read those
MSRs again.

> I guess it could return the last known result, but that wouldn't be
> more meaningful.

Right.

Thanks,

        tglx