On a hyperthreaded system, top and gnome system monitor only report one processor

Jeremie Le Hen jeremie at le-hen.org
Thu Aug 25 13:49:20 GMT 2005


> Speaking of which, is hyperthreading in 6.0 with ULE to the point
> where it actually increases performance for multi-threaded processes
> or parallel compilations (make -j N)? Obviously this is situation
> dependent. I guess the better question is whether HT is able to
> provide a performance increase in 6.0 like it purports to do?
> 
> I've heard that it's not quite "there yet", so I'm cautious about
> enabled SMP support and HT support on a P4-HT system.

It is commonly accepted that HyperThreading decreases performances
on FreeBSD systems.  Both 4BSD and ULE consider dual-core processors
as two separates processors.  This is a problem because dual-core
processors use the same L2 cache for their logical processors (IIRC)
and therefore we cannot schedule whatever threads on them without
taking care of not invalidating the cache too much.

Regards,
-- 
Jeremie Le Hen
< jeremie at le-hen dot org >< ttz at chchile dot org >


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