Date: Wed, 6 Mar 2002 04:16:47 -0600 From: "Mike Meyer" <mwm-dated-1015841808.406799@mired.org> To: Stephen Montgomery-Smith <stephen@math.missouri.edu> Cc: questions@freebsd.org Subject: Re: Which processor? Message-ID: <15493.60559.729973.900130@guru.mired.org> In-Reply-To: <82550640@toto.iv>
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Stephen Montgomery-Smith <stephen@math.missouri.edu> types: > I would like to get a computer to do my processor intensive math > calculations under the FreeBSD operating system. Today I went to my > local computer store, and they offered me a couple of possibilities: > > Asus A7V266-E Motherboard > with 2GHz AMD Athlon XP > or > Tyan S2460 Dual MP Socket A > with dual AMD 1.8 GHz Athlon MP. > > 1. If I run one program, will it only use one of the MP processors? Unless it does something to generate multiple threads of control, it will only use one at a time. It may move back and forth between them. > 2. If I run two seperate programs, will they each use one of the MP > processors, and each go with the speed of 1.8GHz, in effect running the > programs as if they are on two seperate 1.8GHz computers. Right. Except, as noted, that they sometimes move between processors. FreeBSD tries to keep processes on the same CPU, but if it's been waiting long enough and the only free processor is the one it wasn't on before, it'll move. > 3. The salesperson I was speaking two said that these processors were > designed to talk to each other in some way - I think he used the phrase > "sharing threads." What does this mean? A thread is an OS concept. Basically, it encapsulates the runtime state of a program. There are calls to create new threads in the same process, and they can both run at the same time on an SMP system. If your program doesn't create multiple threads, then it will only use one processor. There are lots of things that go into how well the program performs; marketroids have focused on the speed of the processor because it's a single number that can be directly compared, never mind that 200MH PPeo with 512K of cash will run rings around a Celeron with no cache for most applications. The only way to tell how fast a specific program will run on a specific computer is to benchmark it. Can you create a suitable behncharmk? It should use the same memory, but use less time. If so, ask if you can run the benchmark on the machines to see which is faster. <mike -- Mike Meyer <mwm@mired.org> http://www.mired.org/home/mwm/ Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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