linux-kernel - Re: [RFC patch] introduce sys_membarrier(): process-wide memory barrier (v9)

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Date:	Thu, 25 Feb 2010 13:08:51 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	Nick Piggin <npiggin@...e.de>, Chris Friesen <cfriesen@...tel.com>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Nicholas Miell <nmiell@...cast.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>, mingo@...e.hu,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, josh@...htriplett.org,
	dvhltc@...ibm.com, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, Valdis.Kletnieks@...edu, dhowells@...hat.com
Subject: Re: [RFC patch] introduce sys_membarrier(): process-wide memory
 barrier (v9)

On Thu, 2010-02-25 at 12:51 -0500, Mathieu Desnoyers wrote:

> But... either way we chose, we can extend the system call flags and parameters
> as needed, so I think it really should not be part of this initial
> implementation.

I agree here too.

If you have two different tasks doing lockless RCU or what not on shared
memory, it's best to stick with the mb() on the reader side. Yeah, it
makes the performance go down, but heck, I'm really worried about the
crazy complexity that wound need to go into the kernel to prevent this.

-- Steve


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