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Message-Id: <1180978368.4404.29.camel@chaos>
Date: Mon, 04 Jun 2007 19:32:48 +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 09:59 -0700, Stephen Hemminger wrote:
> > > gettimeofday({1180973726, 982754}, NULL) = 0
> > > recv(4, "\0\0\0\0\0\0\0\1\0\0\23\211\0\0\0\0\0\0\0\0\377\377\364"..., 8192, 0) = 8192
> > > gettimeofday({1180973726, 983790}, NULL) = 0
> >
> > Well, gettimeofday() is not affected by the highres code, but
> >
> > > nanosleep({0, 0}, NULL) = 0
> > > nanosleep({0, 0}, NULL) = 0
> >
> > is. The nanosleep call with a relative timeout of 0 returns immediately
> > with highres enabled, while it sleeps at least until the next tick
> > arrives when highres is off. Are there more of those stupid sleeps in
> > the code ?
>
> GLIBC pthread_mutex does it, YES it is a problem!
> Looks like the old behavior is required for ABI compatibility.
>
> iperf server has several threads. One thread is using pthread_mutex_lock
> to wait for the other thread. It looks like pthread_mutex_lock is using
> nanosleep as yield().
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
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