On Sun, Jan 16, 2000 at 10:18:56PM -0700, Wes Peters wrote:
> Michael Bacarella wrote:
> >
> > > Program, when killed with SIGINT, prints all counters and exits.
> > >
> > > Now, as I understand, userspace threads in FreeBSD are preemptive.
> > > So, though my 11 threads are all computational and do not do
> > > any syscalls, sleeps, sched_yield, whatever -- newertheless,
> > > the program should not be stuck in one thread. And it seems to
> > > be sometimes true. But only sometimes!
> >
> > Hmmm, my prior response was pretty much bullshit. It doesn't work
> > for me with 'volatile' at all.
> >
> > [...]
> >
> > Putting a sched_yield(); in the loop body makes sure that they get their
> > fair share, so, other than guessing FreeBSD is at fault, I'm out of ideas. :)
>
> Yup, that does it, but it makes the program several orders of magnitude slower,
> too. Be careful about how much you use sched_yield, you're pushing the system
> into behavior that is outside its normal operating design. FreeBSD wasn't
> designed to re-run the scheduler after 2 or 3 instructions.
In the case of libc_r, a call to sched_yield doesn't result in the system
call sched_yield. Rather, it causes the userland threads scheduler to be
run. There is still plenty of overhead, but running the kernel scheduler
isn't necessarily part of that overhead.
Jason
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