linux-kernel - Re: [PATCH 3/3] WorkStruct: Use direct assignment rather than cmpxchg()

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Message-Id: <1165525597.4698.46.camel@mulgrave.il.steeleye.com>
Date:	Thu, 07 Dec 2006 15:06:37 -0600
From:	James Bottomley <James.Bottomley@...elEye.com>
To:	David Howells <dhowells@...hat.com>
Cc:	Andrew Morton <akpm@...l.org>, torvalds@...l.org,
	davem@...emloft.com, wli@...omorphy.com, matthew@....cx,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH 3/3] WorkStruct: Use direct assignment rather than
	cmpxchg()

On Thu, 2006-12-07 at 20:06 +0000, David Howells wrote:
> Remember: if you have to put a conditional jump in there, it's going to fail
> one way or the other a certain percentage of the time, and that's going to
> cause a pipeline stall, and these ops are used quite a lot.

That we'd have to put a conditional jump in there is an incorrect
assumption on risc machines.  At least on parisc we can do conditional
nullifies in the executing instruction pipeline, so we'd read, nullify
the following write if the bit were set.  We do this a lot in our page
interruption handlers.

James


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