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Date: Mon, 3 Mar 2008 15:53:15 +0200
From: "Pekka Enberg" <penberg@...helsinki.fi>
To: "Nick Piggin" <npiggin@...e.de>
Cc: "Eric Dumazet" <dada1@...mosbay.com>, netdev@...r.kernel.org,
"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
yanmin_zhang@...ux.intel.com, "David Miller" <davem@...emloft.net>,
"Christoph Lameter" <clameter@...r.sgi.com>
Subject: Re: [rfc][patch 3/3] use SLAB_ALIGN_SMP
Hi,
On Mon, Mar 3, 2008 at 3:46 PM, Nick Piggin <npiggin@...e.de> wrote:
> > Maybe we need to use three flags to separate the meanings ?
> >
> > SLAB_HINT_SMP_ALIGN
> > SLAB_HINT_HWCACHE_ALIGN
> > SLAB_HWCACHE_ALIGN /* strong requirement that two objects dont share a
> > cache line */
>
> Possibly, but I'm beginning to prefer that strong requirements should
> request the explicit alignment (they can even use cache_line_size() after
> Pekka's patch to make it generic). I don't like how the name implies
> that you get a guarantee, however I guess in practice people are using it
> more as a hint (or because they vaguely hope it makes their code run
> faster :))
At least historically SLAB_HWCACHE_ALIGN has been just a hint,
although slab tries very hard to satisfy it (see the comments in
mm/slab.c). Why do we need stronger guarantees than that, btw?
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