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

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Date:	Mon, 4 Jun 2007 21:47:59 +0200
From:	Maximilian Engelhardt <maxi@...monizer.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Stephen Hemminger <shemminger@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ulrich Drepper <drepper@...il.com>,
	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>
Subject: Re: iperf: performance regression (was b44 driver problem?)

On Monday 04 June 2007, Ingo Molnar wrote:
> * Stephen Hemminger <shemminger@...ux-foundation.org> 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.
>
> this is the first such app and really, and even for this app: i've been
> frequently running iperf on -rt kernels for _years_ and never noticed
> how buggy its 'locking' code was, and that it would under some
> circumstances use up the whole CPU on high-res timers.

I must admit I don't know much about that topic, but there is one thing I 
don't understand. Why is iperf (even if it's buggy) able to use up the whole 
cpu? I didn't run it as root but as my normal user so it should have limited 
rights. Shouldn't the linux scheduler distribute cpu time among all running 
processes?

Maxi

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