linux-kernel - Re: [PATCH] x86: eliminate redundant/contradicting cache line size config options

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Date:	Wed, 18 Nov 2009 20:52:40 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Nick Piggin <npiggin@...e.de>, Jan Beulich <JBeulich@...ell.com>,
	tglx@...utronix.de, linux-kernel@...r.kernel.org, hpa@...or.com,
	Ravikiran Thirumalai <kiran@...lex86.org>,
	Shai Fultheim <shai@...lemp.com>
Subject: Re: [PATCH] x86: eliminate redundant/contradicting cache line size
 config options

On Thu, 19 Nov 2009 04:56:40 +0100
Ingo Molnar <mingo@...e.hu> wrote:

> 
> * Nick Piggin <npiggin@...e.de> wrote:
> 
> > The only other use for L1 cache size macro is to pack objects to 
> > cachelines better (so they always use the fewest number of lines).
> > But this case is more rare nowadays people don't really count
> > cachelines anymore, but I think even then it makes sense for it to
> > be the largest line size in the system because we don't know how
> > big L1s are, and if you want opimal L1 packing, you likely also
> > want optimal Ln packing.
> 
> We could do that - but then this default of X86_INTERNODE_CACHE_SHIFT:
> 
> +       default "7" if NUMA
> 
> will bite us and turns the 64 bytes L1_CACHE_BYTES into an effective
> 128 bytes value.
> 
> So ... are you arguing for an increase of the default x86 linesize to 
> 128 bytes?

128 is basically always wrong.
(unless you have a P4... but for default really we should not care
about those anymore)


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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