linux-kernel - Re: iperf: performance regression (was b44 driver problem?)

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Date:	Mon, 04 Jun 2007 21:26:18 +0200
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
Cc:	Ulrich Drepper <drepper@...il.com>,
	Maximilian Engelhardt <maxi@...monizer.de>,
	Michael Buesch <mb@...sch.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Jeff Garzik <jgarzik@...ox.com>,
	Gary Zambrano <zambrano@...adcom.com>, netdev@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: iperf: performance regression (was b44 driver problem?)

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


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