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

[Matthias Scheler <tron%zhadum.org.uk@localhost>]

On Mon, Feb 09, 2009 at 08:40:10AM +0000, Andrew Doran 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.

Yes, I completely agree. I only wanted to point out that support for
HT/SMT isn't optimal at the moment.

> The ongoing NUMA work will help with this.

That's good news.

        Kind regards

-- 
Matthias Scheler                                  http://zhadum.org.uk/