linux-kernel - Re: perf events ring buffer memory barrier on powerpc

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Message-ID: <1383512261.4776.21.camel@pasglop>
Date:	Mon, 04 Nov 2013 07:57:41 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Victor Kaplansky <VICTORK@...ibm.com>
Cc:	David Laight <David.Laight@...lab.com>,
	Michael Neuling <mikey@...ling.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Linux PPC dev <linuxppc-dev@...abs.org>,
	Anton Blanchard <anton@...ba.org>, paulmck@...ux.vnet.ibm.com
Subject: Re: perf events ring buffer memory barrier on powerpc

On Fri, 2013-11-01 at 18:30 +0200, Victor Kaplansky wrote:
> "David Laight" <David.Laight@...lab.com> wrote on 11/01/2013 06:25:29 PM:
> > gcc will do unexpected memory accesses for bit fields that are
> > adjacent to volatile data.
> > In particular it may generate 64bit sized (and aligned) RMW cycles
> > when accessing bit fields.
> > And yes, this has caused real problems.
> 
> Thanks, I am aware about this bug/feature in gcc.

AFAIK, this has been fixed in 4.8 and 4.7.3 ... 

Cheers,
Ben.

> -- Victor
> 
> _______________________________________________
> Linuxppc-dev mailing list
> Linuxppc-dev@...ts.ozlabs.org
> https://lists.ozlabs.org/listinfo/linuxppc-dev


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