linux-kernel - Re: MMIO and gcc re-ordering issue

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Date:	Tue, 27 May 2008 09:24:30 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	David Miller <davem@...emloft.net>
Cc:	benh@...nel.crashing.org, linux-arch@...r.kernel.org,
	scottwood@...escale.com, linuxppc-dev@...abs.org,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	tpiepho@...escale.com
Subject: Re: MMIO and gcc re-ordering issue

> It's just another complicated thing for driver authors to get wrong.
> The other side of the coin is of course the cost.
> 
> The only thing I am absolutely sure of is that we should make a
> decision fast, document it, and just stick to it.

It's unfortunate that the __read/___write versions have other different
semantics. The default should definitely be ordered but having un-ordered
ones as an option would be good for zapping the hot paths that matter.

Most I/O paths aren't even worth the thinking time for non-ordered I/O.

Alan
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