NetBSD identifies then shuns cpu core

[Torbjorn Granlund <tg%gmplib.org@localhost>]

I am migrating several systems from FreeBSD to NetBSD in an effort to
consolidate my testing environment.  (NetBSD's Xen support and
up-to-date GNU stuff are the main reasons for this move.)

One system is an "Asrock ION 330", and it behaves quite strange with
NetBSD.

The CPU in this system, an Atom 330 has 2 real cores, but with SMT it
presents 4.  I have however disabled SMT in BIOS, leaving just two CPUs.

NetBSD correctly identifies the two CPUs during boot, and sysctl later
agrees on the number of CPUs.

But it is hard to make cpu0 be used.

With two cpu-bound processes, both seem to be scheduled to cpu1, while
cpu0 is 100% (or close to 100%) idle.

With three cpu-bound processes, both cores become used.

I use /usr/bin/top as the main tool for making these conclusions.  But
timing tests confirm the conclusions; the n seconds of cpu time need 2n
seconds of waal clock time when running two cpu-bound processes.

BIOS bugs?  NetBSD bugs?  Solutions?


Torbjörn