From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sun, 28 Dec 2003 20:47:16 -0500 From: William Josephson To: 9fans@cse.psu.edu Subject: Re: [9fans] hyperthreading Message-ID: <20031229014716.GB90937@mero.morphisms.net> References: <1684.67.31.64.75.1072649552.squirrel@wish.cooper.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1684.67.31.64.75.1072649552.squirrel@wish.cooper.edu> User-Agent: Mutt/1.4.1i Topicbox-Message-UUID: b06568c0-eacc-11e9-9e20-41e7f4b1d025 On Sun, Dec 28, 2003 at 05:12:32PM -0500, Joel Salomon wrote: > ron minnich said: > > hyperthreading: don't waste your time. > > > > hype-r-threading. > > I'm to assume then that hyperthreading is distinct from having multiple > "cores" on a single die (what IBM is doing with some of their machines), > or is this the "hype" you are referring to? Multiple CPUs on one silicon > chip sounds cool to me. Look up the literature on SMT (symetric multithreading). In the case of Intel, the two virtual CPUs do not have the full set of resources available to a single real CPU. The result is a modest improvement in performance for a few specific workloads and has little or negative performance impact on many others (cf. the P4 core generally -- it is a good example of microbenchmarking gone awry in my experience). I have found that with some Unix variants, typically those with underwhelming schedulers for interactive workloads, it helps a bit with keeping the shell and windowing system zippy under load. -WJ