Date: Sat, 4 Apr 1998 23:38:22 -0500 (EST) From: "John S. Dyson" <dyson@FreeBSD.ORG> To: wyma0012@tc.umn.edu (Michael Wyman) Cc: freebsd-questions@FreeBSD.ORG Subject: Re: Multi-processor systems. Message-ID: <199804050438.XAA00486@dyson.iquest.net> In-Reply-To: <Pine.SOL.3.96.980404222242.20427A-100000@garnet.tc.umn.edu> from Michael Wyman at "Apr 4, 98 10:26:43 pm"
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Michael Wyman said: > I have a Dual-P166 machine, and am looking into getting a Unix system (as > Win95 and NT are having problems). I wasn't able to find anything in the > FAQs about multi-processor systems... > > Does FreeBSD support dual processors, and if so, what kind of efficiency > does the second processor get? > FreeBSD-current runs on SMP machines nicely, taking advantage of additional processors. If you are doing compiles, and are not memory limited, you'll notice very close to a 2X speed-up on a P6. On a P5, I would expect less improvement, due to the shared 2nd level cache. FreeBSD tries to allocate memory cache space intelligently, but cannot make up for the typical P5 MB sharing the 2nd level cache. If you are running X windows, the SMP kernels help alot also (due to the client server model of the X environment.) For realtime or fast fork/exec type performance (LL performance), the SMP kernels are slower. Most processes take significantly more time than the fork/exec, and in that case, the SMP kernels will outperform the UP kernels. Note, that the biggest minus about running FreeBSD-current SMP, is that we don't work with all motherboards, but try to. When configuring your system, whether using SMP or UP, the biggest caveat, if you are doing everything right, is to allocate enough swap space. FreeBSD optimizes performance at the expense of swap space. The bottom line, is if you are running a medium loaded workstation, it is very plausible that you'll need 100MB of swap space (or at least 2X your physical memory.) There are ways that you can get by with less, but please don't try (it just ends up being problematical for the users, and a time waste for everyone trying to explain that more swap space is needed.) Be generous with it. Since disks are dirt cheap, consider the $20 worth of disk that FreeBSD needs for swap space as a part of the cost of using the OS. -- John | Never try to teach a pig to sing, dyson@freebsd.org | it just makes you look stupid, jdyson@nc.com | and it irritates the pig. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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