Re: [Lse-tech] Re: multi-queue scheduler update

[Davide Libenzi <davidel@xmail.virusscreen.com>]

On Friday 19 January 2001 13:59, Mike Kravetz wrote:
> On Fri, Jan 19, 2001 at 12:49:21PM -0800, Mike Kravetz showed his lack
>
> of internet slang understanding and wrote:
> > It was my intention to post IIRC numbers for small thread counts today.
> > However, the benchmark (not the system) seems to hang on occasion.  This
> > occurs on both the unmodified 2.4.0 kernel and the one which contains
> > my multi-queue patch.  Therefore, I'm pretty sure it is not something
> > I did. :)
> >
> > Anyone else see anything like this before?  I'll look into the reason
> > for the hang, but it will delay my posting of these numbers.
>
> I think I have found the problem.  Here is a code snippet from the
> benchmark Andrea posted.
>
> void            oneatwork(int thr)
> {
>     int             i;
>     while (!start)              /* don't disturb pthread_create() */
>         usleep(10000);
>
>     actthreads++;
>     while (!stop)
>     {
>         if (count)
>             totalwork[thr]++;
>
>         syscall(158); /* sys_sched_yield() */
>     }
>     actthreads--;
>     pthread_exit(0);
> }
>
> Note that actthreads is a global variable which is being updated
> by multiple threads without any form of synchronization.  Because
> of this actthreads sometimes never goes to zero after all worker
> threads have finished. 

If all threads complete successfully actthreads has to be zero.
If some thread dies, this won't be true.



- Davide
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