Robert Watson wrote: > > On Thu, 12 Apr 2007, Dag-Erling Smørgrav wrote: > >> Randall Stewart <rrs_at_cisco.com> writes: >>> machdep.hyperthreading_allowed: 0 >> >> Note that enabling hyperthreading is more likely to harm performance >> than to help it. You should just disable it in the BIOS, and run a UP >> kernel. > > Historically this has been true, but some more recent results I've seen > suggest that both hyperthreading hardware has improved, and the > efficiency of our SMP implementation and scheduler has lead to it being > more effective used. I would reevaluate this on more modern hardware and > using a more recent kernel before assuming this remains true for your > application. In addition to this, to answer the original question, I remember a commit so that if you disable a cpu (or HT cpu) it doesn't get counted in the CPU % so if you have 2 cpus and disable one hten prior to that commit it was not possible to get > 50% busy but after that commit you could get 100% "of the available CPUs". That fix is not (I believe) in 6.2. I have had applications where HT was useful. They had a mix of integer and floating point work, and were long running, using all of their quanta. Usually with normal work it was a was or a loss. > > Robert N M Watson > Computer Laboratory > University of Cambridge > > > ------------------------------------------------------------------------ > > _______________________________________________ > freebsd-current_at_freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-current > To unsubscribe, send any mail to "freebsd-current-unsubscribe_at_freebsd.org"Received on Thu Apr 12 2007 - 16:05:15 UTC
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