Date: Sun, 18 Sep 2005 12:47:54 -0700 From: Colin Percival <cperciva@freebsd.org> To: "Roger O. Svenning" <roger@audioweb.no> Cc: freebsd-current@freebsd.org Subject: Re: A question about Intel HyperThreading Message-ID: <432DC46A.1000904@freebsd.org> In-Reply-To: <000c01c5bc85$445b3ef0$6401a8c0@aw001> References: <000c01c5bc85$445b3ef0$6401a8c0@aw001>
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Roger O. Svenning wrote: > Due to a fatal hardware failure we replaced one of our AMD based > NeverWinter Nights game -servers with an Intel Pentium 4 one running > 6.0-beta4 > > Look at the top extract below and notice the 50% idle value. > No matter what, it sits at 50% idle all the time when the nwserver > process is running. > > Neither have I ever seen top reporting any process using the other > logical cpu, so basically it sits at 50% idle no matter how much load I > throw at it. Due to a widely-reported security problem, recent versions of FreeBSD disable hyperthreading unless you set the machdep.hyperthreading_allowed tunable in /boot/loader.conf. What you're seeing is a consequence of the mechanism which disables hyperthreading -- the "second thread" is present but is forced to remain idle. > The nwserver service is not multithreaded and I'm guessing it's using > only one of the logical cpus, but are there actually processing power > sitting idle here or is it just a top-weirdness? There is a logical cpu sitting idle, but (due to the way hyperthreading works) there isn't really any processing power sitting idle. > Needless to say I want the nwserver process to be able to use all > processing power available in the cpu. If you want to maximize system performance, you should take SMP out of your kernel configuration; it adds overhead without providing any benefit on a single-processor system. Colin Percival
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