Date: Sun, 27 Mar 2005 21:51:05 +0100 From: RW <list-freebsd-2004@morbius.sent.com> To: freebsd-questions@freebsd.org Subject: Re: hyper threading. Message-ID: <200503272151.06216.list-freebsd-2004@morbius.sent.com> In-Reply-To: <49251524.20050326234521@wanadoo.fr> References: <c6ef380c050326061976f164b@mail.gmail.com> <8C7006AE7E80573-FAC-3B652@mblk-r28.sysops.aol.com> <49251524.20050326234521@wanadoo.fr>
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On Saturday 26 March 2005 22:45, Anthony Atkielski wrote: > em1897@aol.com writes: > > Yes, the theory is very nice; you've done a nice > > job reading Intel's marketing garb. > > I haven't read their marketing materials. I'm simply going by the > technical descriptions I've read of the architecture. > > > However if you don't have a specific hyperthreading-aware scheduler > > and particularly well-written, threaded applications, you'll lose more > > than you'll gain. > > If that were true, then it would be equally true of systems with actual > multiple physical processors. In practice, multiple processors provide > an obvious performance gain, and hyperthreading does, too, although it's > much more modest than the gain obtained from physically independent > processors. The situation is very different. Multiple processors can run multiple processes at the same time. A HT processor can only run two threads from the same process. And most software isn't multithreaded.
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