linux-kernel - Re: [Patch] numa:x86_64: Cacheline aliasing makes for_each_populated

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Message-ID: <20100819220214.GI3043@sgi.com>
Date:	Thu, 19 Aug 2010 17:02:14 -0500
From:	Robin Holt <holt@....com>
To:	"Roedel, Joerg" <Joerg.Roedel@....com>
Cc:	Robin Holt <holt@....com>, Jack Steiner <steiner@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>, Yinghai Lu <yinghai@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Stable Maintainers <stable@...nel.org>
Subject: Re: [Patch] numa:x86_64: Cacheline aliasing makes
 for_each_populated_zone extremely expensive -V2.

> > I don't think this is stable material. It improves performance and does
> > not fix a bug. But I am not the one to decide this :-)
> 
> The only reason I think it qualifies is we are talking about 0.8% of each
> cpus time.  That means that on the 4096 cpu system, we are dedicating
> the equivalent of 32 cpus to just vmstat_update.  That feels like it

Wrong!  0.08%, not 0.8% and therefore 3.2 cpus, not 32.

Sorry for the confusion,
Robin
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