[Ukfreebsd] Disabling hyperthreading on Intel CPUs

andy thomas andy at time-domain.co.uk
Wed Jan 26 08:34:17 GMT 2011

Dos anyone know what happned to the machdep.hyperthreading_allowed 
tunable? It was definitely there in (I think) 5.x but in 8.1 it's not:

 	andy at dell380:~ $ sysctl machdep.hyperthreading_allowed=0
 	sysctl: unknown oid 'machdep.hyperthreading_allowed'

There are some new CPU sysctls in 8.x but they seem to disable cores 
rather than hyperthreading, which is enabled by default in the kernel. I 
would like to be able to turn off hyperthreading at runtime on a large 
number of HP PCs that are fitted with single quad-core CPUs without 
touching the BIO settings.


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