Hyperthreading in 6.x ... still frowned upon?

[Jonathan Noack]

Marc G. Fournier wrote:
> In 4.x, it was a 'shut it off' sort of deal .. my new amd64 don't appear 
> to have it enabled, but my older i386 server that I just upgraded to 6.x 
> does:
> 
> user     pid %cpu %mem   vsz   rss   tt state start        time command
> root      14 104.0  0.0     0     8  ??  RL    11:38AM   0:55.02 [idle: 
> cpu0]
> root      11 99.1  0.0     0     8  ??  RL    11:38AM   0:00.00 [idle: 
> cpu3]
> root      13 99.1  0.0     0     8  ??  RL    11:38AM   0:00.00 [idle: 
> cpu1]
> root      12 98.0  0.0     0     8  ??  RL    11:38AM   0:54.54 [idle: 
> cpu2]
> 
> Is it still something that I should disable, and, if so, how in 6.x?

According to the 6.0 i386 Release Notes, you should use the 
machdep.hyperthreading_allowed sysctl to disable Hyper-Threading.

If you are concerned with security, you should disable it.  If you are 
more concerned with performance, you should test your workload 
with/without Hyper-Threading and choose the configuration which performs 
best.

-Jonathan