Hyperthreading slowdown

[Ian Dowse]

In message <20031004200435.GA60432 at rot13.obsecurity.org>, Kris Kennaway writes:
>Yes, that's because (as discussed in the archives) the kernel treats
>it like an extra, completely decoupled physical CPU and schedules
>processes on it without further consideration.  This is presumably the
>cause of the slowdown, because it's only efficient to use the virtual
>CPU under certain workload patterns.  HTT is not magic performance
>beans.

Try also setting the sysctl variable "machdep.cpu_idle_hlt" to 1, as
it doesn't help to have the idle logical CPUs spinning.

Ian