Re: Hyperthreading/SMT and NetBSD; how well does it work?

[Andrew Doran <ad%netbsd.org@localhost>]

On Sun, Feb 08, 2009 at 09:37:12AM +0000, Matthias Scheler wrote:

> As far as I know NetBSD's kernel doesn't know anything about HT/SMT.
> So if you have a machine with four logical CPUs backed by two physical
> CPUs (or CPU cores) there is a risk that the scheduler will use two
> logical CPUs on the same physical CPU to handle to two jobs. And in
> that case HT/SMT will slow down your system.

This can happen if the system is not loaded, but once the load crosses a
threshold, HT/SMT will be relied upon to provide a benefit.

The ongoing NUMA work will help with this.

Andrew