Subj : Re: threads do not get cpa
To   : comp.programming.threads,comp.sys.sgi.misc
From : Joe Seigh
Date : Sun Aug 07 2005 01:10 pm

azb123@planet.nl wrote:
> Joe,
> thanks for the suggestion!
> I've added the following lines to my code:
> 
> if ((r=pthread_setconcurrency(nthreads)))
>       fprintf(stderr,"Could not set concurrency: %d!\n",r);
> 
> The results are a little bit erratic, sometimes I get the expected
> behavior, i.e. activity_in_top = nthreads*100, and sometimes I get less
> than the expected activity. All this is on a SGI Octane with IRIX
> 6.5.24m (16cpus), no other applications running. I am little bit
> puzzled now, could that be a strange effect of the IRIX scheduler?
> 
> I also noticed another oddity: When I run my program with more threads
> it's slower than with just a single one, e.g.:
> 
> nthreads cpu-time wall-clock time
> 1             30         30
> 2            140         70
> 3            452        154
> 
> Do you have further suggestions?
> 
Could be lock contention from either the locks in your program or ones
in a routine you are calling.  Also if you were running Linux I'd
suspect Linux's brain damaged signaling but you're using IRIX which
I don't know if it has the same problem.


-- 
Joe Seigh

When you get lemons, you make lemonade.
When you get hardware, you make software.

.