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SubjectRe: [Lse-tech] Re: multi-queue scheduler update
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. I changed actthreads to be an atomic and
used atomic operations to manipulate it. With this change, I was
able to complete one round of testing which I had not been able to
do in the past.

Does anyone maintain this benchmark code? The changes I indicate
above should be made. If you need more specifics I can provide
them.

--
Mike Kravetz mkravetz@sequent.com
IBM Linux Technology Center
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