Author: Robert Hyatt
Date: 11:54:03 09/29/01
Go up one level in this thread
On September 29, 2001 at 10:41:37, Miguel A. Ballicora wrote: >On September 29, 2001 at 10:01:11, Robert Hyatt wrote: > >>On September 28, 2001 at 00:00:43, Miguel A. Ballicora wrote: >> >>>On September 27, 2001 at 18:06:34, Olaf Jenkner wrote: >>> >>>>>If you can consistently produce a speedup of 3.0, then I can time- >>>>>slice that same algorithm on one cpu and get a speedup of 1.5. And I can do it >>>>>for _any_ alpha/beta algorithm you do in parallel. Every time. And using your >>>>>code, it will be easy for me to do it. >>>>> >>>>It's a good explanation. Some people seem to believe to perpetuum mobiles. >>> >>>Some believe that objects heavier than air will never fly. >>>Everybody knows, that's against physics. >>> >>>Regards, >>>Miguel >> >> >>I think you worded that wrong. Airplanes are heavier than air and have been >>flying for 100 years now. I think you meant the bumble-bee, because no one >>believed they could move their wings rapidly enough to produce the lift required >>to get them off the ground. > >I worded right, I was sarcastic to answer a sarcastic message. > >>There is a difference between "believed to be impossible" and "known to be >>impossible." > >Exactly my point. > >>super-linear speedups are provably impossible. I've already given the simple >>proof. > >Then, I missed it. If you refer to doing two threads "slicing the time" this >requires an overhead, and that means that using two processors are > 2.0 or ><2.0, who knows. (it could be 2.0001, or more, we do not know how future cpus >will behave). Still, that was not the interesting part of the discussion. The >interesting part was if an algorithm with two threads could be better than one. > It requires no overhead to mention. Every N milliseconds the processor handle a timer interrupt. I choose that point to switch to the other thread. The cost is minimal. You overlook the fact that the parallel search _also_ has its own kind of overhead problems... that would be eliminated in the approach needed for a serial version (ie no atomic locks that are very slow... etc.) >Super-linear speedups are "probably" impossible but so far I did not see that >they are "provably" impossible. I would settle with "They are believed to be >impossible". > >Regards, >Miguel They simply _are_ impossible. Unless you believe in perpetual motion, infinite compression, a fire that will burn forever, etc.
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