Date: Sun, 16 Jan 2000 23:41:09 -0500 (EST) From: Michael Bacarella <mbac@nyct.net> To: Alexander Litvin <archer@lucky.net> Cc: hackers@FreeBSD.ORG Subject: Re: Preemptiveness of FreeBSD threads Message-ID: <Pine.BSF.4.05.10001162336110.179-100000@bsd1.nyct.net> In-Reply-To: <20000116225044.C601@unknown.nowhere.org>
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> 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.
If I put: printf ("running %d\n", pthread_self());
right before the counter loop, I only get one thread telling me about
itself.
Seems like a scheduler problem. Perhaps it is treating all threads as a
logical unit and assigning them a global priority, and selecting the same
thread to suck up all of it's time, each time.
A "successful" run probably happens on busier systems where other factors
mess with scheduling -- but I haven't verified this.
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. :)
-MB
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