linux-kernel - Re: [PATCH] x86: use cpufreq_quick_get() for /proc/cpuinfo "cpu MHz" again

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Date:   Tue, 14 Nov 2017 16:06:12 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        WANG Chao <chao.wang@...oud.cn>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Len Brown <len.brown@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Mathias Krause <minipli@...glemail.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH] x86: use cpufreq_quick_get() for /proc/cpuinfo "cpu MHz" again

On Tue, Nov 14, 2017 at 4:04 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Tue, Nov 14, 2017 at 3:53 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
>> Current head + Raphaels patch:
>>
>> real    0m0.029s
>> user    0m0.000s
>> sys     0m0.010s
>>
>> So that patch is actually slower.
>
> Oh it definitely is expected to be slower, because it does the IPI to
> all the cores and actually gets their frequency right.
>
> It was the old one that we had to revert (because it did so
> sequentially) that was really bad, and took something like 2+ seconds
> on Ingo's 160-core thing, iirc.

Looked it up. Ingo's machine "only" had 120 cores, and he said

    fomalhaut:~> time cat /proc/cpuinfo  >/dev/null
    real    0m2.689s

for the bad serial case, so yeah, it looks "a bit" better than it was ;)

             Linus