Re: Inconsistent timing results of multithreaded program on an SMP machine.

[Con Kolivas <kernel@kolivas.org>]

On Sun, 20 Nov 2005 21:50, Marcel Zalmanovici wrote:
> On Sun, 20 Nov 2005 21:35, Muli Ben-Yehuda wrote:
> > On Sun, Nov 20, 2005 at 09:28:13PM +1100, Con Kolivas wrote:
> > > Ok I've had a look at the actual program now ;) Are you timing the time
> > > it takes to completion of everything?
> > >
> > > This part of your program:
> > >          for (i= 0; i<8; i++)
> > >                      pthread_join(tid[i], NULL);
> > >
> > > Cares about the order the threads finish. Do you think this might be
> > > affecting your results?
> >
> > I don't see why it should matter. Depending on the order the threads
> > finish, we will always wait in pthread_join until the last one
> > finishes, and then do between 0 and 7 more pthread_joins that should
> > return immediately (since the last one has already finished).
>
> If it was instant it shouldn't matter. I'm aware of that in theory, but
> there
> have certainly been reports of pthread_join taking quite a while happening
> in
> a sort of lazy/sloppy way. I don't know why this is the case but I wondered
>
> if it was showing up here.
>
> I've looked through the detailed run results and found this:
>
> Thread DS 0, TID = 7646
> Thread DS 0, TID = 7645
> Thread DS 1, TID = 7648
> Thread DS 1, TID = 7650
> Thread DS 2, TID = 7651
> Thread DS 2, TID = 7652
> Thread DS 3, TID = 7653
> Thread DS 3, TID = 7654
> Main exit ...
> real 23.25
>
> As you can see except the first 2 threads all finished in order they were
> created. With the average being at about 16.5 this is a high result and
> thread order was almost ideal.

Ok, but how long does pthread_join actually take to complete?

Cheers,
Con

P.S. Lotus notes is terrible for a mailer isn't it?