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

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Message-ID: <1262853136.4049.81.camel@laptop>
Date:	Thu, 07 Jan 2010 09:32:16 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	akpm@...ux-foundation.org, josh@...htriplett.org,
	tglx@...utronix.de, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, laijs@...fujitsu.com, dipankar@...ibm.com
Subject: Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory
 barrier

On Wed, 2010-01-06 at 21:02 -0800, Paul E. McKenney wrote:
> 
> Beats the heck out of user-mode signal handlers!!!  And it is hard
> to imagine groveling through runqueues ever being a win, even on very
> large systems.  The only reasonable optimization I can imagine is to
> turn this into a no-op for a single-threaded process, but there are
> other ways to do that optimization.
> 
> Reviewed-by: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>

Then imagine someone doing:

 while (1)
  sys_membarrier();

on your multi node machine, see how happy you are then.

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