Author: Miguel A. Ballicora
Date: 07:41:37 09/29/01
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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. 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
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