FreeBSD 6-STABLE and HyperThreading

[Kris Kennaway]

On Sat, Dec 31, 2005 at 03:30:29PM +0100, Niek Bouman wrote:
> Hi,
> 
> I have a pc with a pentium4 cpu with HT support running FreeBSD 6-STABLE.
> 
> In the GENERIC kernel, SMP is turned off by default. I am wondering 
> whether it is useful to enable HT-support.
> 
> In the usenet discussions, I have seen a lot about the HT security flaw 
> that was detected a while ago. Also I read about some rumours saying 
> that the system performance decreases with HT enabled in freebsd, 
> because freebsd thinks that there are 2 physical cpu's and adapts the 
> workload over them in a way that is not suitable for just one physical 
> HT processor.
> 
> Could someone give advice on whether it's wise to enable HT-support in 
> 6-STABLE?
> 
> And, is the following correct: enabling SMP (=HT in this case?) is 
> nothing more than adding "options SMP" to the kernel config file and 
> then do a kernel rebuild & reinstall ?
> 
> And what about the scheduler? Is the usage of ULE recommended, or should 
> i stick the old one?

These questions are answered all the time, but the answer is that HT
usually hurts performance, and so does ULE.

Kris
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