linux-kernel - Re: [PATCH 0/2] jump label: 2.6.38 updates

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Message-ID: <1297705095.5226.136.camel@laptop>
Date:	Mon, 14 Feb 2011 18:38:15 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mike Frysinger <vapier@...too.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Jason Baron <jbaron@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	hpa@...or.com, mingo@...e.hu, tglx@...utronix.de,
	andi@...stfloor.org, roland@...hat.com, rth@...hat.com,
	masami.hiramatsu.pt@...achi.com, fweisbec@...il.com,
	avi@...hat.com, davem@...emloft.net, sam@...nborg.org,
	ddaney@...iumnetworks.com, michael@...erman.id.au,
	linux-kernel@...r.kernel.org, Chris Metcalf <cmetcalf@...era.com>,
	dhowells <dhowells@...hat.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	"heiko.carstens" <heiko.carstens@...ibm.com>,
	benh <benh@...nel.crashing.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH 0/2] jump label: 2.6.38 updates

On Mon, 2011-02-14 at 12:29 -0500, Mike Frysinger wrote:
> On Mon, Feb 14, 2011 at 12:27, Peter Zijlstra wrote:
> > On Mon, 2011-02-14 at 12:18 -0500, Steven Rostedt wrote:
> >> blackfin, seems to be doing quite a lot. Not sure if it is required, but
> >> that may need a bit of investigating to understand why it does the
> >> raw_uncached thing.
> >
> > From what I can tell its flushing its write cache, invalidating its
> > d-cache and then issue the read, something which is _way_ overboard.
> 
> not when the cores in a SMP system lack cache coherency

But atomic_read() is completely unordered, so even on a non-coherent
system a regular read should suffice, any old value is correct.

The only problem would be when you could get cache aliasing and read
something totally unrelated.

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