Author: Tom Kerrigan
Date: 01:14:42 04/04/00
Go up one level in this thread
On April 03, 2000 at 22:48:46, Christophe Theron wrote: >On April 03, 2000 at 22:08:49, Tom Kerrigan wrote: > >>On April 03, 2000 at 20:10:00, Christophe Theron wrote: >> >>>I would suggest to go for the Athlon. The PIII really sucks, for my program at >>>least. I don't know why, but the PIII-450 is slower than the K6-2 400 for Chess >>>Tiger (close to 10% slower!). >> >>The K6-2 has much shorter pipelines than the PIII. That makes it significantly >>faster, but also keeps the clock speeds relatively low. > > >I suppose this explains why the K6-2 can execute more instruction per cycle than >the PIII: each pipeline "step" in the K6-2 does more work. On the other hand, >all this work to do means that the clock speed cannot be pushed too far. Is this >what you mean? Exactly. I think the main problem is with branch mispredictions. If you start speculatively executing instructions after a branch, and you guessed wrong, you have to flush the pipes and start over. Restarting a 12-stage pipeline really kills you because you have to wait 12 cycles for the first instruction to finish. I've heard that the PIII wastes 30% of its time due to mispredictions. >>The reason the Athlon may be better than the PIII for computer chess is the huge >>L1 caches. I suspect the integer core of the Athlon is pretty much equivalent to >>the PIII's. > > >Athlon or K6-2, it is the same thing for Tiger (at the same clock speed I mean). >So I'm not sure the L1 cache makes a difference here. And, at least for my >program, it seems that the Athlon integer core is better than the PIII's. I can't remember how much L1 cache the K6-2 has, but the Athlon has much more (128k). The Athlon also has a much faster L2 cache. So the K6-2 might be inherently faster than an Athlon, but once in a while it gets stuck waiting on memory, so they end up the same. -Tom
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