linux-kernel - Re: um: this_cpu_cmpxchg16b

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Message-Id: <201104122227.03688.richard@nod.at>
Date:	Tue, 12 Apr 2011 22:27:03 +0200
From:	Richard Weinberger <richard@....at>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
	linux-kernel@...r.kernel.org,
	user-mode-linux-devel@...ts.sourceforge.net, hpa@...or.com
Subject: Re: um: this_cpu_cmpxchg16b_emu

Am Dienstag 12 April 2011, 21:22:47 schrieb Pekka Enberg:
> On Tue, Apr 12, 2011 at 08:41:11PM +0200, Richard Weinberger wrote:
> >> Am Dienstag 12 April 2011, 20:10:37 schrieb Christoph Lameter:
> >> > On Tue, 12 Apr 2011, Richard Weinberger wrote:
> >> > > This patch implements this_cpu_cmpxchg16b_emu() for UML.
> >> > 
> >> > Is this really necessary? Just undefine CONFIG_CMPXCHG_LOCAL for UML
> >> > and the asm code will not be used.
> >> 
> >> UML includes arch/x86/Kconfig.cpu which defines CONFIG_CMPXCHG_LOCAL
> >> automatically. Just disabling CONFIG_CMPXCHG_LOCAL for UML is IMHO not
> >> very nice. When chpxchg is available also UML should use it...
> 
> On Tue, Apr 12, 2011 at 10:20 PM, Tejun Heo <tj@...nel.org> wrote:
> > Ugh... I'd really like to avoid things like this for UML.  Is there
> > any SLUB performance sensitive workload running on UML?  I've never
> > seen any UML in production environment.  Wouldn't it be better to keep
> > things simple?
> 
> Yes, it would be. :-)

Okay. Then let's keep it simple. :-)
I'll disable CONFIG_CMPXCHG_LOCAL for UML.

Has someone looked at my this_cpu_cmpxchg16b_emu() implementation,
is it correct? Especially the call to C stuff.
I've tested it, it works fine.

Thanks,
//richard
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