Beta 3 Crash with machdep.hlt_logical_cpus

Scott Long scottl at
Tue Sep 7 09:39:53 PDT 2004

Rusty Nejdl wrote:
> I am running on a Dual 1.8 Ghz Xeon box and I have hyperthreading turned
> on in the BIOS such that it appears that I have 4 processors.  I am not
> physically at the machine right now but wanted to report a problem I had
> today.  I changed machdep.hlt_logical_cpus from 0 to 1 while running and
> the system completely froze up.  I don't know what error occurred as I
> wasn't at the machine and have rebooted since then.  I do know that using
> 5.2 I was able to do this and the sytstem would move all the processes to
> the correct CPU's.  Not sure if anyone else has seen this.
> Rusty Nejdl

This is a known problem with the SCHED_ULE scheduler.  Fixing it doesn't
appear to be trivial, so we are considering other alternatives for
RELENG_5 and 5.3, including switching back to the 4BSD scheduler.  The
4BSD scheduler also appears to be much more stable than ULE, especially
with kernel preemption enabled.


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