[Beowulf] Opinions of Hyper-threading?
gdjacobs at gmail.com
Wed Feb 27 09:50:02 EST 2008
Ashley Pittman wrote:
> I saw a talk which said SMT was worth a maximum of 20% on power5 and
> often performed worse than if it had been tured off. This correlates
> well with my experience of it on Intel CPUs.
> It seems most people, myself included, benchmark(ed) with hyperthreading
> disabled in the bois/at boot time and again with hyperthreading enabled
> and jobs scheduled to the meta-cpu's. Not surprisingly the performance
> often isn't all that different despite having twice as many cpu's
> however the variance is much higher when it's enabled.
> I believe there should be a third way whereby the virtual cpu's are
> enabled and running but not used to run parallel jobs, more to run any
> background tasks the OS should happen to throw at them, if we were to go
> down this road I could use the reclaimed cycles to do something sensible
> with marshaling data for non-blocking MPI operations. At least part of
> the reason this wasn't tested before is scheduler support for
> hyperthreading and CPU binding, by the time kernel support was good
> enough to do the tests I'd have liked to have done the window was closed
> and hardware technology had moved on.
I was wondering about the Power 6 because it is an in order design. To
me, hyperthreading and OoOE are optimizing in the same area, and I
wanted to know if SMT is more beneficial where there is no OoOE.
Geoffrey D. Jacobs
Beowulf mailing list, Beowulf at beowulf.org
To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
More information about the Beowulf