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

[Con Kolivas <kernel@kolivas.org>]

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. 

Cheers,
Con