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

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Date:	Tue, 15 Feb 2011 13:27:02 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	simoneau@....uri.edu
Cc:	will.newton@...il.com, hpa@...or.com, matt@...sole-pimps.org,
	rostedt@...dmis.org, peterz@...radead.org, jbaron@...hat.com,
	mathieu.desnoyers@...ymtl.ca, 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, sam@...nborg.org, ddaney@...iumnetworks.com,
	michael@...erman.id.au, linux-kernel@...r.kernel.org,
	vapier@...too.org, cmetcalf@...era.com, dhowells@...hat.com,
	schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
	benh@...nel.crashing.org
Subject: Re: [PATCH 0/2] jump label: 2.6.38 updates

From: Will Simoneau <simoneau@....uri.edu>
Date: Tue, 15 Feb 2011 16:11:23 -0500

> Note how the cache and cache coherence protocol are fundamental parts of this
> operation; if these instructions simply bypassed the cache, they *could not*
> work correctly - how do you detect when the underlying memory has been
> modified?

The issue here isn't L2 cache bypassing, it's local L1 cache bypassing.

The chips in question aparently do not consult the local L1 cache on
"ll" instructions.

Therefore you must only ever access such atomic data using "ll"
instructions.
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