linux-kernel - Re: [patch] x86_64: Avoid too many remote cpu references due to /proc/stat

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Message-ID: <20070713100329.GE16304@infradead.org>
Date:	Fri, 13 Jul 2007 11:03:29 +0100
From:	Christoph Hellwig <hch@...radead.org>
To:	Ravikiran G Thirumalai <kiran@...lex86.org>
Cc:	Andi Kleen <ak@...e.de>, Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	"Shai Fultheim (Shai@...lex86.org)" <shai@...lex86.org>
Subject: Re: [patch] x86_64: Avoid too many remote cpu references due to /proc/stat

On Thu, Jul 12, 2007 at 05:06:16PM -0700, Ravikiran G Thirumalai wrote:
> Too many remote cpu references due to /proc/stat.
> 
> On x86_64, with newer kernel versions, kstat_irqs is a bit of a problem.
> On every call to kstat_irqs, the process brings in per-cpu data from all
> online cpus.  Doing this for NR_IRQS, which is now 256 + 32 * NR_CPUS
> results in (256+32*63) * 63 remote cpu references on a 64 cpu config.
> /proc/stat is parsed by common commands like top, who etc, causing
> lots of cacheline transfers
> 
> This statistic seems useless. Other 'big iron' arches disable this.
> Can we disable computing/reporting this statistic?  This piece of
> statistic is not human readable on x86_64 anymore,

At which point we might just remove it completely..

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