GSoC: Add SMT/HT awareness to DragonFlyBSD scheduler

Francois Tigeot ftigeot at
Sat Jul 28 23:35:53 PDT 2012


On Sun, Jul 29, 2012 at 01:13:04AM +0300, Mihai Carabas wrote:
> > This machine is an old-school dual-Opteron 252 system and doesn't have
> > any hyperthreading support at all.
> > Having an hyperthreading-aware scheduler shouldn't make any difference;
> > what could explain the above performance differences ?
> >
> The heuristics I tested are about SMT (cache hotness heuristic - always
> tries to schedule on the last CPU that had run on. If we can't schedule on
> it and we are an cpu-bound process, we can wait for a tick to be ellected
> by our home CPU. If we aren't pulled after that, we are eligible and ready
> to be pulled on no matter what cpu). So, this heuristic doesn't have
> anything to do with HT (hyper threading).

Not wanting to nitpick, but for me SMT = Simultaneous Multi Threading, of
which Hyper Threading is a particular implementation.

Nothing to do with cache-hotness heuristics per se :)

Francois Tigeot

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