Author: Tom Kerrigan
Date: 01:08:16 05/23/00
Go up one level in this thread
On May 23, 2000 at 03:08:52, Bruce Moreland wrote: >On May 23, 2000 at 02:39:30, Tom Kerrigan wrote: > >>For some reason, people seem to believe that unless you're using 100% of your >>processor all the time, you could make do with a slower processor. >> >>Okay, maybe your processor spends the VAST majority of its time waiting on you. >>But that's not what matters. What matters is how much time you spend waiting on >>the processor. >> >>I have an 800MHz Pentium III at work. It is very noticably faster than my 400MHz >>Celeron at home. Even if I'm just browsing the web, I definitely prefer using my >>work computer because I have to wait on it half as long. > >I'm all for faster computers, I just don't see what the benefit is of having two >processors in a computer that's used by the typical home or business user. I >may have to add "yet" to the previous sentence, but maybe not. > >People need more processors if: > >1) They do two CPU-intensive things at once. The typical user doesn't do this >very much. > > or > >2) The application they are using can divide work. The typical application does >not divide work. There are lots of reasons for this. We have a chicken and egg >problem due to most computers being single processor. Another reason is that >many tasks are inherently sequential. Another reason is that many tasks take >very little time to execute, so multiprocessor overhead doesn't make a lot of >sense. Another reason is that many tasks that take a lot of time take a lot of >time due to bottlenecks other than the processor. And finally, if you have a >task that is significant enough that you could notice time saved due to an >additional processor, and it is able to be broken down into parts that can be >done concurrently, multiprocessor code is often difficult to design, build, >debug, document, and maintain. Adding multiprocessor features to most programs >is a poor design decision. > >I am not a Luddite. If you have your normal single-threaded compute-bound app, >and you double processor speed, the improvement is immediate, and I approve of >this kind of improvement, most definitely. But take one of the many commercial >chess apps and put it on a quad processor machine and see what happens -- >nothing. This is also true of essentially *any* current app you can buy that >does anything. > >Chess is actually a great case for multiprocessor computers, so for us, they are >cool. > >But it will be a while until the typical user sees much advantage to adding >another processor, I think. > >I see that multiple processor machines are becoming more common, but I can't >understand why, and I can't understand why this trend would continue. > >bruce Sorry, I didn't read your post carefully and didn't realize you were talking specifically about multiple processors. "Multiprocessing" will hopefully become widespread soon thanks to multi-threading processors. This is an idea that [mainly] Compaq/Alpha has been promoting. The idea is that if you have a processor with 2 execution units, you can do one of two things: 1) Use both units to execute a single thread; unfortunately, one of the units will probably be idle a lot of the time. This is what most chips do now. 2) Use one unit per thread, in the case that two threads are running. That way, neither unit spins. The chip real-estate overhead for multithreading is evidently pretty small. Hopefully it will be incorperated in mainstream chips soon. -Tom
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