netdev - Re: [rfc][patch 1/3] slub: fix small HWCACHE

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Message-ID: <20080307023223.GD21185@wotan.suse.de>
Date:	Fri, 7 Mar 2008 03:32:23 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Christoph Lameter <clameter@....com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, yanmin_zhang@...ux.intel.com,
	dada1@...mosbay.com
Subject: Re: [rfc][patch 1/3] slub: fix small HWCACHE_ALIGN alignment

On Thu, Mar 06, 2008 at 06:26:49PM -0800, Christoph Lameter wrote:
> On Fri, 7 Mar 2008, Nick Piggin wrote:
> 
> > That's just because you (apparently still) have a misconception about what
> > the flag is supposed to be for. It is not for aligning things to the start
> > of a cacheline boundary. It is not for avoiding false sharing on SMP. It
> 
> The alignment of the object to the start of a cacheline is the obvious 
> meaning and that is also reflected in the comment in slab.h.

It doesn't say start of cache line. It says align them *on* cachelines.
2 32 byte objects on a 64 byte cacheline are aligned on the cacheline.
2.67 24 bytes objects on a 64 byte cacheline are not aligned on the
cacheline.

Anyway, if you want to be myopic about it, then good luck with that.

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