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

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Message-ID: <20070510230003.5861c4b9@the-village.bc.nu>
Date:	Thu, 10 May 2007 23:00:03 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, Randy Dunlap <randy.dunlap@...cle.com>
Subject: Re: [PATCH] "volatile considered harmful" document

> In Ethernet drivers, for example, it is common for the network card to
> maintain a pointer in host memory the the latest descriptor written; you
> will generally have a loop of the form:
> 
> 	while ((this_pointer = *pointer_ptr) > my_last_pointer) {
> 		for (pkt = my_last_pointer; pkt < this_pointer; pkt++)
> 			receeive_packet(pkt);
> 		my_last_pointer = this_pointer;
> 	}
> 
> pointer_p can then be a volatile pointer into said coherent memory.

True but you can happily use rmb/wmb for this which are clearer and fit
the rest of the Linux model better.

Alan
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