Date: Wed, 1 Mar 2006 15:26:34 -0500
From: Benjamin LaHaise <bcrl@kvack.org>
To: "Bryan O'Sullivan" <bos@pathscale.com>
Cc: Andi Kleen <ak@suse.de>, linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] Define wc_wmb, a write barrier for PCI write combining
Message-ID: <20060301202634.GC4081@kvack.org>
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On Wed, Mar 01, 2006 at 12:05:07PM -0800, Bryan O'Sullivan wrote:
> This section also makes it clear yet again that wmb() is absolutely not
> sufficient to get program store order semantics in the presence of WC;
> you *have* to use an explicit synchronising instruction of some kind.

The semantics your code seems to care about are not those of a memory 
barrier (which deals with ordering), but of a flush of the write combining 
buffers.  That's an important high level distinction as they are implemented 
differently across architectures.  Please rename the macro something like 
flush_wc() and document it as such, at which point I remove my objection.

		-ben
-- 
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