linux-kernel - Re: [patch] tlb flush_data: replace per

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Message-ID: <20090113123317.GA29926@elte.hu>
Date:	Tue, 13 Jan 2009 13:33:17 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ravikiran G Thirumalai <kiran@...lex86.org>,
	Frederik Deweerdt <frederik.deweerdt@...og.eu>,
	andi@...stfloor.org, tglx@...utronix.de, hpa@...or.com,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] tlb flush_data: replace per_cpu with an array


* Peter Zijlstra <peterz@...radead.org> wrote:

> > -	char pad[SMP_CACHE_BYTES];
> > -} ____cacheline_aligned;
> > +	char pad[X86_INTERNODE_CACHE_BYTES];
> > +} ____cacheline_internodealigned_in_smp;
> 
> That will make the below array 8*4096 bytes for VSMP, which pushes the 
> limit for memory savings up to 256 cpus.

VSMP is a clustering solution (default-disabled) that pushes 
L1_CACHE_BYTES to 4096 bytes (4K). That is an extremely large alignment 
that pushes up the BSS size ten-fold (!), so no generic Linux distribution 
enables it. 32K compared to 9MB bloat caused by 4K cachelines is a drop in 
the ocean.

	Ingo
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