Re: GSoC: Add SMT/HT awareness to DragonFlyBSD scheduler

[Alex Hornung <ahornung@xxxxxxxxx>]

On 28/07/12 23:13, Mihai Carabas wrote:
>     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).

The newer heuristics Mihai implemented are not specific to SMT/HT, but
affect any multi-core machine, pretty much. It takes topology in general
into account; that is: sockets, cores on the socket, and if available,
threads in a core (SMT/HT).

In other words, his scheduling changes affect any SMP machine.

HTH,
Alex