Date: Thu, 12 Apr 2007 11:05:14 -0700 From: Julian Elischer <julian@elischer.org> To: Robert Watson <rwatson@FreeBSD.org> Cc: Ivan Voras <ivoras@fer.hr>, Randall Stewart <rrs@cisco.com>, freebsd-current@freebsd.org, Janardhan Iyengar <iyengar@conncoll.edu>, =?ISO-8859-1?Q?Dag-Erling_Sm=F8rgrav?= <des@des.no>, Brad Penoff <penoff@cs.ubc.ca> Subject: Re: CPU utilization Message-ID: <461E74DA.3020402@elischer.org> In-Reply-To: <20070412153930.A99718@fledge.watson.org> References: <461E0078.3050001@cisco.com> <evl00c$89j$1@sea.gmane.org> <461E092B.4080001@cisco.com> <86d529zxci.fsf@dwp.des.no> <20070412153930.A99718@fledge.watson.org>
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Robert Watson wrote: > > On Thu, 12 Apr 2007, Dag-Erling Smørgrav wrote: > >> Randall Stewart <rrs@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@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-current > To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org"
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