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

Thomas Gleixner
2007-06-04T19:01:44Z

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