linux-kernel - Re: [PATCH] "volatile considered harmful" document

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Message-ID: <20070513235341.GA4270@havoc.gtf.org>
Date:	Sun, 13 May 2007 19:53:41 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Bill Davidsen <davidsen@....com>
Cc:	Krzysztof Halasa <khc@...waw.pl>,
	Robert Hancock <hancockr@...w.ca>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH] "volatile considered harmful" document

On Sun, May 13, 2007 at 07:26:13PM -0400, Bill Davidsen wrote:
> Krzysztof Halasa wrote:
> >Robert Hancock <hancockr@...w.ca> writes:
> >>You don't need volatile in that case, rmb() can be used.

> >rmb() invalidates all compiler assumptions, it can be much slower.

It does not invalidate /all/ assumptions.


> Yes, why would you use rmb() when a read of a volatile generates optimal 
> code?

Read of a volatile is guaranteed to generate the least optimal code.
That's what volatile does, guarantee no optimization of that particular
access.

	Jeff



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