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From: "Bryan O'Sullivan" <bos@pathscale.com>
To: linux-kernel@vger.kernel.org, discuss@x86-64.org,
	Andi Kleen <ak@suse.de>
Subject: Why is wmb() a no-op on x86_64?
Date: Wed, 18 Jan 2006 08:23:37 -0800	[thread overview]
Message-ID: <1137601417.4757.38.camel@serpentine.pathscale.com> (raw)

Hi, Andi -

I notice that wmb() is a no-op on x86_64 kernels unless
CONFIG_UNORDERED_IO is set.  Is there any particular reason for this?
It's not similarly conditional on other platforms, and as a consequence,
in our driver (which requires a write barrier in some situations for
correctness), I have to add the following piece of ugliness:

#if defined(CONFIG_X86_64) && !defined(CONFIG_UNORDERED_IO)
#define ipath_wmb() asm volatile("sfence" ::: "memory")
#else
#define ipath_wmb() wmb()
#endif

	<b


             reply	other threads:[~2006-01-18 16:23 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2006-01-18 16:23 Bryan O'Sullivan [this message]
2006-01-18 16:29 ` Why is wmb() a no-op on x86_64? Andi Kleen
2006-01-18 16:52   ` Bryan O'Sullivan
2006-01-18 17:06     ` Jes Sorensen
2006-01-18 17:23       ` Bryan O'Sullivan
2006-01-18 17:31       ` [discuss] " Andi Kleen
2006-01-19 10:03         ` Jes Sorensen
2006-01-18 20:07       ` Roland Dreier

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