linux-kernel - Re: [RFC 4/4] cputime: remove scaling

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Date:	Thu, 11 Apr 2013 17:06:39 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Stanislaw Gruszka <sgruszka@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>, hpa@...or.com,
	rostedt@...dmis.org, akpm@...ux-foundation.org, tglx@...utronix.de,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC 4/4] cputime: remove scaling

On Thu, Apr 11, 2013 at 10:36:35AM +0200, Stanislaw Gruszka wrote:
> > I really prefer robust kernel side accounting/instrumentation.
> 
> We have CONFIG_IRQ_TIME_ACCOUNTING and CONFIG_VIRT_CPU_ACCOUNTING_GEN.
> Perhaps we can change to use one of those options by default. I wonder
> if the additional performance cost related with them is really something
> that we should care about. Are there any measurement that show those
> will make performance worse ?

CONFIG_IRQ_TIME_ACCOUNTING also make use of scaling. And CONFIG_VIRT_CPU_ACCOUNTING_GEN
involves too much overhead on IO-bound workloads. It's mostly good for
undisturbed userspace bound workloads (few IRQs, few exceptions, few syscalls).
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