linux-kernel - Re: [PATCH tip/tracing/markers] new probes manager

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Message-ID: <20081027182655.GA11494@elte.hu>
Date:	Mon, 27 Oct 2008 19:26:55 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH tip/tracing/markers] new probes manager


* Mathieu Desnoyers <compudj@...stal.dyndns.org> wrote:

> * Mathieu Desnoyers (mathieu.desnoyers@...ymtl.ca) wrote:
> > * Lai Jiangshan (laijs@...fujitsu.com) wrote:
> > > 
> > > this patch use a new probes manager for marker.
> > > 
> > > the most important benefit of this patch is:
> > > 	1) smp_rmb() is removed from the critical path. as we know rmb()
> > > 	   is very expensive.
> > > 
> > 
> > Do you have performance measurements for this ? On x86 it's a nop,
> > AFAIK.
> 
> My statement above is inexact : x86_64 uses lfence for rmb(). But
> numbers would still be welcome.

yes, the statement that rmb() is very expensive looks dubious. It is 
absolutely cheap everywhere.

	Ingo
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