From mboxrd@z Thu Jan  1 00:00:00 1970
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH] x86: use cpufreq_quick_get() for /proc/cpuinfo "cpu MHz"
 again
Date: Wed, 15 Nov 2017 08:54:26 +0100
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To: Ingo Molnar <mingo@kernel.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>, Linus Torvalds <torvalds@linux-foundation.org>, Thomas Gleixner <tglx@linutronix.de>, 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>, 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 Wed, Nov 15, 2017 at 08:43:58AM +0100, Ingo Molnar wrote:
> 
> * Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> 
> > On Wednesday, November 15, 2017 1:06:12 AM CET Linus Torvalds wrote:
> > > On Tue, Nov 14, 2017 at 4:04 PM, Linus Torvalds
> > > <torvalds@linux-foundation.org> 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.
> > > 
> > > 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 ;)
> > 
> > OK, so may I queue it up?
> > 
> > I don't think I can get that to work substantially faster anyway ...
> 
> The new version is OK I suppose:
> 
>   Acked-by: Ingo Molnar <mingo@kernel.org>
> 
> I also think that /proc/cpuinfo is a pretty bad interface for many uses - I 
> personally only very rarely need the cpuinfo of _all_ CPUs.
> 
> We we should eventually have /proc/cpu/N/info or so, so that 99% of the times 
> cpuinfo is needed to report bugs we can do:
> 
> 	cat /proc/cpu/0/info
> 
> With maybe also the following variants:
> 
> 	/proc/cpu/first/
> 	/proc/cpu/last/
> 	/proc/cpu/current/
> 
> ... to the first/last/current CPUs.

We started to move this info into /sys/devices/cpu/ in individual files,
but that got stalled due to a lack of review and general "freak out" by
the ARM maintainers :)

Hopefully that patch set will come back soon so people can review it
properly.

thanks,

greg k-h