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

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Date:   Wed, 15 Nov 2017 19:05:22 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
cc:     Ingo Molnar <mingo@...nel.org>,
        "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 Wed, 15 Nov 2017, Linus Torvalds wrote:
> On Tue, Nov 14, 2017 at 11:43 PM, Ingo Molnar <mingo@...nel.org> wrote:
> Again, try that "cat" example again, and time it.
> 
> (And yes, I also know that "cpu*/cpufreq" is a symlink, but the direct
> names are illogical, and no faster for me. Try it if you like:
> 
>   time cat /sys/devices/system/cpu/cpufreq/policy*/scaling_cur_freq > /dev/null

Just for the fun of it I tried. It's exactly the same time as /proc/cpuinfo
with the reverted patch which did the full IPI thing, i.e. >4 seconds on
that machine.

Not a surprise because those files do the full IPI thing as well.

Thanks,

	tglx