linux-kernel - Re: [PATCH -tip/core/rcu 1/6] Cleanups and fixes for RCU in face of heavy CPU-hotplug stress

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Date:	Fri, 21 Aug 2009 16:17:21 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Josh Triplett <josht@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org, dvhltc@...ibm.com,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, hugh.dickins@...cali.co.uk,
	benh@...nel.crashing.org
Subject: Re: [PATCH -tip/core/rcu 1/6] Cleanups and fixes for RCU in face
	of heavy CPU-hotplug stress


* Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:

> I would not trust this architecture for synchronization tests. 
> There has been reports of a hardware bug affecting the cmpxchg 
> instruction in the field. The load fence normally implied by the 
> semantic seems to be missing. AFAIK, AMD never acknowledged the 
> problem.

If cmpxchg was broken i'd be having far worse problems and very 
widely so.

FYI, this was the same box i prototyped/developed -rt on, which uses 
cmpxchg for _everything_.

That's not a proof of course (it's near impossible to prove the lack 
of a bug), but it's sure a strong indicator and you'll need to 
provide far more proof of misbehavior before i discount a bona fide 
regression on this box.

	Ingo
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