Subject: Re: iperf: performance regression (was b44 driver problem?)
From: Thomas Gleixner <tglx@linutronix.de>
To: Stephen Hemminger <shemminger@linux-foundation.org>
Cc: Ulrich Drepper <drepper@gmail.com>,
	Maximilian Engelhardt <maxi@daemonizer.de>,
	Michael Buesch <mb@bu3sch.de>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-wireless <linux-wireless@vger.kernel.org>,
	Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
	Jeff Garzik <jgarzik@pobox.com>,
	Gary Zambrano <zambrano@broadcom.com>, netdev@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Ingo Molnar <mingo@elte.hu>
In-Reply-To: <20070604105158.31ede1f5@freepuppy>
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Date: Mon, 04 Jun 2007 21:00:47 +0200
Message-Id: <1180983647.4404.38.camel@chaos>
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Sender: linux-wireless-owner@vger.kernel.org

On Mon, 2007-06-04 at 10:51 -0700, Stephen Hemminger wrote:
> > I doubt that. This is in the iperf code itself.
> > 
> > void thread_rest ( void ) {
> > #if defined( HAVE_THREAD )
> > #if defined( HAVE_POSIX_THREAD )
> >     // TODO add checks for sched_yield or pthread_yield and call that
> >     // if available
> >     usleep( 0 );
> > 
> > ----------^^^^
> > 
> > It results in a nanosleep({0,0}, NULL)
> > 
> > 	tglx
> > 
> 
> Yes, the following patch makes iperf work better than ever.
> But are other broken applications going to have same problem.
> Sounds like the old "who runs first" fork() problems.

Not really. The fork() "who runs first" problem is nowhere specified.

usleep(0) is well defined:

.... If the value of useconds is 0, then the call has no effect.

So the call into the kernel has been wrong for quite a time.

	tglx