linux-kernel - Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier

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Date:	Fri, 8 Jan 2010 16:20:43 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	akpm@...ux-foundation.org, josh@...htriplett.org,
	tglx@...utronix.de, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	laijs@...fujitsu.com, dipankar@...ibm.com
Subject: Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory
	barrier

On Fri, Jan 08, 2010 at 06:53:38PM -0500, Mathieu Desnoyers wrote:
> * Steven Rostedt (rostedt@...dmis.org) wrote:
> > Well, if we just grab the task_rq(task)->lock here, then we should be
> > OK? We would guarantee that curr is either the task we want or not.
> 
> Hrm, I just tested it, and there seems to be a significant performance
> penality involved with taking these locks for each CPU, even with just 8
> cores. So if we can do without the locks, that would be preferred.

How significant?  Factor of two?  Two orders of magnitude?

							Thanx, Paul
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