8.1-PRERELEASE: CPU packages not detected correctly
jhb at freebsd.org
Thu Jul 15 18:45:54 UTC 2010
On Thursday, July 15, 2010 1:56:11 pm Andriy Gapon wrote:
> on 15/07/2010 19:57 Oliver Fromme said the following:
> > In topo_probe(), cpu_high is 0xd, so topo_probe_0xb() is
> > called. But the cpuid 0xb instruction doesn't seem to
> > return useful data: All values are zero already in the
> > first level, so cpu_cores remains 0.
> > Back in topo_probe(), there is a fallback if cpu_cores is
> > stil 0: It assigns mp_ncpu to cpu_cores, so it gets 8
> > which is wrong.
> > I patched topo_probe() so it calls topo_probe_0x4() after
> > topo_probe_0xb() if cpu_cores is still 0. I think this
> > is a better fallback procedure. With this patch, cpu_cores
> > gets the value 4 which is the correct one, finally:
> > FreeBSD/SMP: Multiprocessor System Detected: 8 CPUs
> > FreeBSD/SMP: 2 package(s) x 4 core(s)
> Thank you for debugging this issue!
> Not sure if this is the best patch that there can be, but its direction is
> definitely correct.
> As the Intel document says (translated to our x86 mp_machdep.c terms):
> if cpu_high >= 0xb then we should execute cpuid_count(0xb, 0, p) and examine EBX
> value (p), only if it's non-zero should we proceed with topo_probe_0xb(),
> otherwise we should fall back to topo_probe_0x4, etc.
> I think that your addition achieves this effect, perhaps just not as explicitly as
> I would preferred.
Maybe have topo_probe_0xb() explicitly call topo_probe_0x4() if EBX is 0?
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