linux-kernel - Re: [PATCH] cpufreq: Report if CPU doesn't report boost technologies

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Date:   Wed, 20 Feb 2019 10:52:17 +0000
From:   Erwan Velu <e.velu@...teo.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Erwan Velu <erwanaliasr1@...il.com>
CC:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "open list:CPU FREQUENCY SCALING FRAMEWORK" 
        <linux-pm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: Report if CPU doesn't report boost technologies


Le 20/02/2019 à 11:41, Rafael J. Wysocki a écrit :
> On Wed, Feb 20, 2019 at 11:11 AM Erwan Velu <erwanaliasr1@...il.com> wrote:
>> There is some rare cases where CPB (and possibly IDA) are missing on processors.
>> This is the case fixed by commit f7f3dc00f612 ("x86/cpu/AMD: Fix erratum 1076 (CPB bit)") and following.
>>
>> In such context, the boost status isn't reported by /sys/devices/system/cpu/cpufreq/boost.
> So I'm not really sure why the extra message is needed.  It looks like
> this message will always be printed (with debug output enabled) if the
> current cpufreq driver is acpi-cpufreq and the boost attribute is not
> present in sysfs, which only is the case if CPB/IDA aren't there.
>
> Does it provide any additional information, then?

When you know and read the code, yes this patch is too obvious.

As a user when I was troubleshooting why the boost entry was _not_ 
populated on one CPU and was populated on another.

Running acpi-cpufreq with dyndbg, I would have found useful to get that 
hint.

So that could helps users that never read that part of the code and 
which are tricked into that configuration.

Erwan,