linux-kernel - Re: [PATCH 00/10] vtime: Delay cputime accounting to tick

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Date:   Tue, 6 Dec 2016 15:20:55 +1100
From:   Paul Mackerras <paulus@...abs.org>
To:     Frederic Weisbecker <fweisbec@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Tony Luck <tony.luck@...el.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Rik van Riel <riel@...hat.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Stanislaw Gruszka <sgruszka@...hat.com>
Subject: Re: [PATCH 00/10] vtime: Delay cputime accounting to tick

On Tue, Dec 06, 2016 at 03:32:13AM +0100, Frederic Weisbecker wrote:
> This follows up Martin Schwidefsky's patch which propose to delay
> cputime accounting to the tick in order to minimize the calls to
> account_system_time() and alikes as these functions can carry quite some
> overhead:
> 
> 	http://lkml.kernel.org/r/20161121111728.13a0a3db@mschwide
> 
> The set includes Martin's patch, rebased on top of tip:sched/core and
> latest s390 changes, and extends it to the other implementations of
> CONFIG_VIRT_CPU_ACCOUNTING_NATIVE (powerpc and ia64) along with a few
> core changes to adapt the whole.
> 
> Only built-tested though as I don't have access to any of these archs.

The patches look reasonable at a quick look.  I assume that to test
them, we would want to run a guest in an overcommitted system, so as
to get some steal time.  Do you have any more specific suggestions as
to what to run as a test?  Just run some benchmark and see if the
user/system/irq times look reasonable?  Or do you have something more
quantitative?

Paul.