linux-kernel - Re: [patch 00/10] [RFC] SLUB patches for more functionality, performance and maintenance

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Message-Id: <20070709.124359.38710002.davem@davemloft.net>
Date:	Mon, 09 Jul 2007 12:43:59 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	clameter@....com
Cc:	linux-kernel@...r.kernel.org, linux-mm@...r.kernel.org,
	suresh.b.siddha@...el.com, corey.d.gough@...el.com,
	penberg@...helsinki.fi, akpm@...ux-foundation.org
Subject: Re: [patch 00/10] [RFC] SLUB patches for more functionality,
 performance and maintenance

From: Christoph Lameter <clameter@....com>
Date: Mon, 9 Jul 2007 08:45:42 -0700 (PDT)

> On Sat, 7 Jul 2007, David Miller wrote:
> 
> > From: Christoph Lameter <clameter@....com>
> > Date: Sat, 07 Jul 2007 20:49:52 -0700
> > 
> > > A cmpxchg is less costly than interrupt enabe/disable
> > 
> > This is cpu dependant, and in fact not true at all on Niagara
> > and several of the cpus in the UltraSPARC family.
> 
> Hmmm... So have alternate aloc/free paths depending on the cpu?

As Andi seemed to imply I don't even think cmpxchg is faster than
interrupt enable/disable on current generation AMD x86_64 chips, so
are you targetting this optimization solely at Intel x86 Core Duo
32-bit chips?  That's the only one I can see which will benefit from
this.  Are you going to probe the cpu sub-type and patch SLUB?

I really don't think this optimization is wise as even if you
could decide at build time, it's going to be a maintainence and
debugging nightmare to have to field bug reports given two different
locking schemes.

Please reconsider this change, thanks.

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