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

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Message-ID: <20080307031044.GF21185@wotan.suse.de>
Date:	Fri, 7 Mar 2008 04:10:44 +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 06:54:19PM -0800, Christoph Lameter wrote:
> > 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.
> 
> 2 32 byte objects means only one is aligned on a cache line.
> 
> Certainly cacheline contention is reduced and performance potentially 
> increased if there are less objects in a cacheline.
> 
> The same argument can be made of aligning 8 byte objects on 32 byte 
> boundaries. Instead of 8 objects per cacheline you only have two. Why 8?
> 
> Isnt all of this a bit arbitrary and contrary to the intend of avoiding 
> cacheline contention?

No, it *is not about avoiding cacheline contention*. As such, the rest
of what you wrote below about smp_align etc is rubbish.

Can you actually read what I posted?

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