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: <1180983647.4404.38.camel@chaos>
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Date: Mon, 04 Jun 2007 21:26:18 +0200
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On Mon, 2007-06-04 at 21:00 +0200, Thomas Gleixner wrote:
> > 
> > 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.
> 

Just for clarification: I'm not saying that we should break the (broken)
user space ABI. I'm going to work out a patch which prints out a warning
(limited number per boot) and emulating the old behavior by a call to
yield() along with an entry into (mis)feature-removal.txt.

	tglx