Re: sched_yield() on "SCHED_FIFO"

NIIBE Yutaka (gniibe@chroot.org)
Fri, 30 Jul 1999 17:54:16 +0900

Kuniyasu SUZAKI writes:
> The supposed action of my program depended on the Round Robin
> scheduling on 1 CPU. The program produced two processes and they would
> be executed alternately, because it yielded each other on 1 CPU. The
> main problem is one process monopolied a CPU even if it executed
> sched_yield().

Oops, I had not understood the code you provided. Now, I see your
point.

I think that I've found the cause of the problem.

--------------------------- kernel/sched.c
asmlinkage int sys_sched_yield(void)
{
spin_lock_irq(&runqueue_lock);
if (current->policy == SCHED_OTHER) <---------- This line.
current->policy |= SCHED_YIELD;
current->need_resched = 1;
move_last_runqueue(current);
spin_unlock_irq(&runqueue_lock);
return 0;
}
---------------------------

This line was introduced on November 1998 in the patch-2.1.127.
Without this conditional (set SCHED_YIELD flag regardless of policy),
I guess it works fine.

Could someone try? I don't have single CPU machine at hand.

-- 
Niibe Yutaka


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