linux-kernel - Re: [PATCH 3/4] cputime: Consolidate vtime handling on context switch

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Message-ID: <20120815172219.4e4d5ef5@de.ibm.com>
Date:	Wed, 15 Aug 2012 17:22:19 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Tony Luck <tony.luck@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 3/4] cputime: Consolidate vtime handling on context
 switch

On Tue, 14 Aug 2012 16:16:49 +0200
Frederic Weisbecker <fweisbec@...il.com> wrote:

> The archs that implement virtual cputime accounting all
> flush the cputime of a task when it gets descheduled
> and sometimes set up some ground initialization for the
> next task to account its cputime.
> 
> These archs all put their own hooks in their context
> switch callbacks and handle the off-case themselves.
> 
> Consolidate this by creating a new account_switch_vtime()
> callback called in generic code right after a context switch
> and that these archs must implement to flush the prev task
> cputime and initialize the next task cputime related state.

That change requires that the accounting for the previous process
can be done before finish_arch_switch() completed. With the old
code the architecture could to the accounting call in the middle
of finish_arch_switch, that is not possible anymore. Dunno if this
is relevant or not. For s390 the new code should work fine.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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