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From: Andi Kleen <ak@suse.de>
To: Arjan van de Ven <arjan@infradead.org>
Subject: Re: [RFC PATCH 02/33] Add sync bitops
Date: Wed, 19 Jul 2006 14:54:40 +0200
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Cc: Chris Wright <chrisw@sous-sol.org>, linux-kernel@vger.kernel.org,
       virtualization@lists.osdl.org, xen-devel@lists.xensource.com,
       Jeremy Fitzhardinge <jeremy@goop.org>, Andrew Morton <akpm@osdl.org>,
       Rusty Russell <rusty@rustcorp.com.au>, Zachary Amsden <zach@vmware.com>,
       Ian Pratt <ian.pratt@xensource.com>,
       Christian Limpach <Christian.Limpach@cl.cam.ac.uk>,
       Christoph Lameter <clameter@sgi.com>
References: <20060718091807.467468000@sous-sol.org> <20060718091948.747619000@sous-sol.org> <1153216601.3038.16.camel@laptopd505.fenrus.org>
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On Tuesday 18 July 2006 11:56, Arjan van de Ven wrote:
> On Tue, 2006-07-18 at 00:00 -0700, Chris Wright wrote:
> > plain text document attachment (synch-ops)
> > Add "always lock'd" implementations of set_bit, clear_bit and
> > change_bit and the corresponding test_and_ functions.  Also add
> > "always lock'd" implementation of cmpxchg.  These give guaranteed
> > strong synchronisation and are required for non-SMP kernels running on
> > an SMP hypervisor.
>
> Hi,
>
> this sounds really like the wrong approach; you know you're compiling
> for xen, so why not just make set_bit() and the others use the lock'd
> instructions at compile time?

I guess because they only need it for a small subset of set_bits.

-Andi