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

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Date:   Wed, 15 Nov 2017 08:54:26 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        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>,
        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, Nov 15, 2017 at 08:43:58AM +0100, Ingo Molnar wrote:
> 
> * Rafael J. Wysocki <rjw@...ysocki.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@...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 ;)
> > 
> > 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@...nel.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