linux-kernel - Re: [PATCH] printk: use this_cpu_{read|write} api on printk

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Message-ID: <alpine.DEB.2.00.1011261125270.13524@router.home>
Date:	Fri, 26 Nov 2010 11:27:00 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	a.p.zijlstra@...llo.nl, heiko.carstens@...ibm.com,
	tglx@...utronix.de, mingo@...e.hu
Subject: Re: [PATCH] printk: use this_cpu_{read|write} api on
 printk_pending

On Fri, 26 Nov 2010, Eric Dumazet wrote:

> Le vendredi 26 novembre 2010 à 11:11 -0600, Christoph Lameter a écrit :
>
> > I thought sanity tests do not apply for performance testing scenarios?
> >
>
> CONFIG_DEBUG_PREEMPT

You really enable that option for performance testing?

> > smp_processor_id() is usually a simple per cpu data access and very fast.
> >
>
> Sure, but when its already in a register, its better to use the
> register ;)

Well that increases register pressure in the caller. There may be no need
to handle the current processor number in the caller.