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

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Message-ID: <20090114144115.GF10720@gambetta>
Date:	Wed, 14 Jan 2009 15:41:15 +0100
From:	Frederik Deweerdt <frederik.deweerdt@...og.eu>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Ravikiran G Thirumalai <kiran@...lex86.org>,
	tglx@...utronix.de, hpa@...or.com, linux-kernel@...r.kernel.org
Subject: Re: [patch] tlb flush_data: replace per_cpu with an array

On Wed, Jan 14, 2009 at 10:08:11AM +0100, Andi Kleen wrote:
> 
> > > It also would save some memory
> > > on most distros out there (Ubuntu x86_64 has NR_CPUS=64 by default).
> 
> As pointed out several times this claim in the changelog is incorrect.
> Please fix it.
> 
> A correct description would be:
> 
> - This patch wastes memory of one configured cache line for each CPU 
> on systems with less than 8 cores (e.g. 896 bytes on a 1 core system
> with CONFIG_GENERIC_CPU/ cache line size 128)
> It saves some memory on systems with more than 8 cores (one cache
> line size for each core above 8)
To be fair, it also depends on whenever HOTPLUG_CPU is on or not (if it
is we allocate NR_CPUS percpu sections). In that case, which is Ubuntu's
and Fedora's, we do save memory.
This would make for a fairly long changelog, how about a link to this
thread, and removing the NR_CPUS bit?

Regards,
Frederik
> 
> -Andi
> 
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