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

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Message-ID: <CA+55aFycTaZjKg1SGujkMrOX5WmUyWHvy2ujzaV8jefOfDPy_Q@mail.gmail.com>
Date:   Fri, 10 Nov 2017 11:11:16 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     WANG Chao <chao.wang@...oud.cn>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        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 Thu, Nov 9, 2017 at 2:30 PM, Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> c_start() can run aperfmperf_snapshot_khz() on all CPUs upfront (say
> in parallel), then wait for a while (say 5 ms; the current 20 ms wait
> is overkill) and then aperfmperf_snapshot_khz() can be run once on
> each CPU in show_cpuinfo() without taking the "stale cache" threshold
> into account.

Yeah, that won't work.

What could work is to do that "smp_call_function_many()" at open time,
and *not* set the "wait" flag, but do it entirely asynchronously.

But I don't think that's an option for 4.14 ;(

So I guess I'll have to revert.

            Linus