only one logical CPU used in Xeon

Oliver Fromme olli at
Tue Mar 10 14:31:39 PDT 2009

Julian Elischer wrote:
 > Robert Heron wrote:
 > > Hyperthreading is enabled in BIOS, but the variable:
 > > 
 > > machdep.hyperthreading_allowed
 > > 
 > > is '0' by default in FreeBSD 6.2R :(((
 > > I just changed it now to '1' and all cores in all CPUs started to work :)))
 > > 
 > > Very simple change and so much power more :)
 > well certainly more power used..

That's true.

 > It would be a good idea to do benchmarks on your workload
 > to check if it actually helps. This is is because
 > Hyperthreading on some cpu models actually reduces throughput
 > on some workloads because it thrashes the shared cache more.

No need for benchmarks here, because Robert's processors
don't do hyperthreading at all.  FreeBSD 6.2 recognized
the *cores* as logical HT processors, so he needs to
set hyperthreading_allowed in order to enable the cores.

Of course, the better solution is to update to a more
recent release, such as 6.4 or even 7.1.  His 6.2 is
more than 2 years old and contains lots of known bugs,
of which the wrong recognition of cores is a relatively
harmless one.

Best regards

Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing b. M.
Handelsregister: Registergericht Muenchen, HRA 74606,  Geschäftsfuehrung:
secnetix Verwaltungsgesellsch. mbH, Handelsregister: Registergericht Mün-
chen, HRB 125758,  Geschäftsführer: Maik Bachmann, Olaf Erb, Ralf Gebhart

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