Confused about HyperThreading and Performance

[Christopher Vance]

On Wed, Nov 12, 2003 at 06:07:58PM -0500, John Baldwin wrote:
>APIC is not on by default for 4.9, it will be for 5.2.  4.9 does have
>HTT on by default when you build an SMP kernel though.  Did you include
>'options HTT' in your 4.8 SMP kernel?  If not, you aren't actually
>using your second CPU.  Also, as someone else mentioned, setting
>'machdep.cpu_idle_hlt=1' can be useful on some HTT systems.  However,
>p4's have a problem with their interrupt routing that can leave the
>second CPU halted for a long time if you do that.

Just because you have a cpu with HTT doesn't mean you can use it.
Your motherboard and BIOS also need to be aware of it, and enable it.

-- 
Christopher Vance