From mboxrd@z Thu Jan  1 00:00:00 1970
From: Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] x86: use cpufreq_quick_get() for /proc/cpuinfo "cpu MHz"
 again
Date: Wed, 15 Nov 2017 09:47:11 +0100 (CET)
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>, WANG Chao <chao.wang@ucloud.cn>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, Vikas Shivappa <vikas.shivappa@linux.intel.com>, Kate Stewart <kstewart@linuxfoundation.org>, Len Brown <len.brown@intel.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Philippe Ombredanne <pombredanne@nexb.com>, Mathias Krause <minipli@googlemail.com>, the arch/x86 maintainers <x86@kernel.org>, Linux PM <linux-pm@vger.kernel.org>, "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>

On Tue, 14 Nov 2017, Linus Torvalds wrote:
> On Tue, Nov 14, 2017 at 3:53 PM, Thomas Gleixner <tglx@linutronix.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.
> 

Tired brain did not connect it to the revert.

On that machine with ea0ee3398877: Revert "x86: CPU: Fix up "cpu MHz" in
/proc/cpuinfo" reverted it takes:

real	0m4.497s
user	0m0.012s
sys	0m0.000s

> It sounds like the current patch is slower, but likely acceptable
> considering that you get the right results now ..

Correct and the factor 10, i.e. 30ms vs. 3ms is not horrible, while the 4.5
seconds are.

Thanks,

	tglx