Author: Slater Wold
Date: 14:44:54 11/21/01
Go up one level in this thread
On November 21, 2001 at 15:30:25, Robert Hyatt wrote: >On November 21, 2001 at 14:04:57, Slater Wold wrote: > >>On November 21, 2001 at 13:33:14, Robert Hyatt wrote: >> >>>On November 21, 2001 at 11:52:09, Slater Wold wrote: >>> >>>>On November 21, 2001 at 11:19:08, Robert Hyatt wrote: >>>> >>>>>On November 21, 2001 at 11:05:00, Slater Wold wrote: >>>>> >>>>>> >>>>>>As I have found positions where the NPS search is 2.5x faster, but it solves the >>>>>>solution in 4x faster than a single cpu. >>>>>> >>>>>>Dann and I had this "super" linear discussion before. >>>>>> >>>>>>Seems like it would even out, eventually. But like I said, I believe you. And >>>>>>I'll do it to solution now. (But of course, I'll still look at the NPS!) :) >>>>>> >>>>> >>>>> >>>>>First, two cpus is going to have a _hard_ time searching 2.5x the raw >>>>>nodes per second. I have no idea how that might happen, unless there is a >>>>>bug in the node-counting that sometimes counts nodes twice. >>>> >>>>Sorry. I've seen positions where it will search 1.8x the NPS and solve it 4x >>>>faster. >>> >>>That is not uncommon at all... >>> >>> >>> >>>> >>>>I was just reversing your comment. >>>> >>>>>Second, "super-linear" can happen on occasional positions. But as you said, >>>>>it will average out over multiple positions so that the speedup simply can not >>>>>be >2.0 for two processors on average. I was in the middle of the super-linear >>>>>speedup discussion. I hope it stays "at rest" now. :) >>>> >>>>I've seen it happen a time or two. I've found a solution one go, and can never >>>>get it again. (Happened more than once with DJ7.) >>>> >>>>>I have seen several cases of spectacular speedups, but then I have also seen >>>>>an equal number of horrible speedups. Bruce once sent me one that produced >>>>>a particularly ugly result on Crafty, But I can't seem to locate the thing >>>>>at present... >>>> >>>>I think I've only seen 1 or 2. But I have seen a LOT that are greater than the >>>>speedup of the NPS speedup. In other words, it takes the SMP less nodes to find >>>>the solutions, that the 1 CPU. >>>> >>> >>>That is the classic super-linear speedup situation. bad move ordering >>>corrected by the parallel search taking 'em two at a time. >>> >>> >>> >>>>>In any case, NPS is kind of like engine RPM. It should increase linearly with >>>>>the number of processors, assuming the parallel algorithm is good at keeping >>>>>both cpus busy all the time and doesn't have one (or more) sitting around >>>>>waiting excessively. But RPM has nothing to do with vehicle speed, because >>>>>of losses along the drive train. The MPH value (time to solution) is the thing >>>>>that wins races (or games). >>>> >>>>HUM. Now you're picking a subject I am _very_ familiar with. RPM's and and MPH >>>>aren't _DIRECTLY_ related. >>>> >>>>IE: >>>> >>>>If you have a car that has a 4.11 gear ratio with 351c.i. motor, that is getting >>>>400 HP at 5750RPM, it SHOULD go 12's in the 1/4 mile. (Depending on weight.) >>>>Let's just say, it goes 12.5 @ 119MPH. >>>> >>>>Now, let's say you install an aluminum driveshaft. Your RPM's are going to >>>>increase. Same setup, same everything, it will probably get 400HP at 5900 RPM. >>>>And if you run the 1/4 mile again, I would guarantee 12.3's at the SAME MPH. >>>>Maybe, you'll get 1 or 2 more MPH. You're going .2 seconds faster, but the MPH >>>>isn't changing. RPM doesn't = MPH, but the faster you can rev, the faster you >>>>can get to that top MPH. Unless your gears are wacky. >>> >>>You do better than I do there. I've never seen an alum drive shaft increase >>>RPM. I have seen it decrease the time to reach a particular RPM, but I don't >>>see why it would increase the actual RPM since it doesn't take much energy to >>>keep a driveshaft rotating, it just takes energy to accelerate it down the >>>track, and energy to accelerate the RPM level of the shaft itself. >> >>On a fox body Mustang, an aluminum driveshaft over the stock driveshaft will >>improve the cars 1/4 mile times by around .2 seconds. I've seen it done more >>than a dozen times. I never meant to imply that the RPM's would go higher, but >>that the time to get to X RPM would get shorter. And I know a lighter >>driveshaft will put the powerband of the car slightly higher. I also know it >>will not help your cars top speed. Only off the line accleration. >> >>>Your above example can't work however, as you didn't change the rear end ratio, >>>and if you reach a higher rpm you will _definitely_ reach a higher top speed as >>>well. RPM and MPH are exactly proportional if everything else (tire diameter >>>and final drive ratio) remains constant. >> >>You're correct. If you're in 4th gear at 3k RPM, you will always be going X >>MPH. It's only if you change gears that will change. However, the off the line >>accleration is what's going to get you those better times. You're getting to X >>RPM faster, and therefore X MPH faster, which means you're going to gain SOME >>ground. > > >That's actually what we are racing, in fact. :) 1990 coupe. > >Goes like the blazes... I've had several. Namely a 351 '92. It flew. You'll have to e-mail me about yours. There are a few video's of mine on the internet.
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