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

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Message-ID: <alpine.DEB.2.00.1011261109500.13524@router.home>
Date:	Fri, 26 Nov 2010 11:11:22 -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:

> I guess you read the changelog too fast ;)

No I only read the code.... ;-)

> I posted this patch after noticing printk_needs_cpu() was always used
> for the current cpu.

Ok.

> We have other functions around, that always work for the current cpu.

Ok.

> We pass cpu as a parameter, mostly because smp_processor_id() was a bit
> expensive in old kernels, and is still expensive because of sanity
> tests.

I thought sanity tests do not apply for performance testing scenarios?

smp_processor_id() is usually a simple per cpu data access and very fast.

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