linux-kernel - Re: [RFC PATCH 02/33] Add sync bitops

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Message-Id: <200607191454.41019.ak@suse.de>
Date:	Wed, 19 Jul 2006 14:54:40 +0200
From:	Andi Kleen <ak@...e.de>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Chris Wright <chrisw@...s-sol.org>, linux-kernel@...r.kernel.org,
	virtualization@...ts.osdl.org, xen-devel@...ts.xensource.com,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Andrew Morton <akpm@...l.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Zachary Amsden <zach@...are.com>,
	Ian Pratt <ian.pratt@...source.com>,
	Christian Limpach <Christian.Limpach@...cam.ac.uk>,
	Christoph Lameter <clameter@....com>
Subject: Re: [RFC PATCH 02/33] Add sync bitops

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
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