Bill Moran <wmoran@potentialtech.com> writes:
> Just for an additional viewpoint. I'm finishing up a project based on FreeBSD
> and PostgreSQL. The target server is a Dual 2.4G Intel machine. I have tested
> the application with hyperthreading enabled and disabled. To all appearances,
> enabling hyperthreading makes the box act like a quad, with the expected increase
> in processing capability - _for_this_application_.
>
> I have also heard the claims and seen the tests that show hyperthreading
> occasionally decreasing performance. I think in the end, you just have to
> test your particular application to see how it reacts.
My understanding is that the case where HT hurts is precisely your case. When
you have two real processors with HT the kernel will sometimes schedule two
jobs on the two virtual processors on the same real processor leaving the two
virtual processors on the other real processor idle.
As far as I know a single processor machine with HT does not benefit from
disabling HT.
--
greg