Author: Vincent Diepeveen
Date: 16:31:34 05/07/04
Go up one level in this thread
On May 07, 2004 at 12:02:28, Robert Hyatt wrote: >On May 07, 2004 at 11:53:29, Andreas Guettinger wrote: > >>On May 07, 2004 at 04:38:00, Vincent Diepeveen wrote: >> >>>On May 06, 2004 at 19:03:48, martin fierz wrote: >>> >>>>aloha! >>>> >>>>bob posted some crafty logfiles running a 24-position test set on his ftp site >>>>(for anyone else crazy enough to repeat what i did: >>>>ftp.cis.uab.edu/pub/hyatt/smpdata) >>>> >>>>these are logfiles of crafty running as single CPU, dual, or quad; on opterons. >>>>i took the last completed ply on the single CPU set for each position (marked by >>>>-> in the logfile, i hope...), wrote down the time to complete this ply, and did >>>>this for all logfiles. there are 9 of these, 4 repeats for 2 and 4 CPUs. i >>>>computed the speedup for time-to-finish-ply-X for each of the multi-CPU runs >>>>with the following results: >>>> >>>>2 CPUs: >>>>1.961 +- 0.093 >>>>1.888 +- 0.074 >>>>1.846 +- 0.078 >>>>1.763 +- 0.084 >>>> >>>>4 CPUs: >>>>3.15 +- 0.15 >>>>3.29 +- 0.20 >>>>3.06 +- 0.12 >>>>3.19 +- 0.13 >>>> >>>>now, is there any meaning to this, and if yes, what? >>>> >>>>point #1 to make is that the numbers here are mutually consistent with each >>>>other, given the error margins quoted. which should show those skeptical of this >>>>statistical approach that it makes sense to do it this way, rather than to just >>>>write "i measured speedup 3.1". >>>> >>>>point #2 is that the speedup on 4 CPUs on average is 3.17 in this test, which >>>>might be one point for bob in the duel with vincent; although i suspect that the >>>>speedup depends on the hardware architecture - i will leave this question to the >>>>parallel computing experts though... >>> >>>Bob has tested the SMP version 1 cpu versus SMP version 2 or 4 cpus. The single >>>cpu version of crafty is just hardly existing because of a stupid thread pointer >>>which is a constant. Optimizing that crafty is 5% faster for sure in time single >>>cpu at opteron. >> >>I don't understand that. What does that mean? >> >>regards >>Andy > >Ever heard of "the fog of war"? This is "the fog of vincent". > >In crafty, I pass a pointer to a "TREE struct" around so that each thread can >use a different struct for their local tree state. This is done even with mt=0 >or when Crafty is compiled with no SMP support. Vincent claims it would speed >Crafty up by 5% if the pointer were removed. That would be neat as it didn't >slow me down 5% when I added the pointer. > >But that's irrelevant because Vincent has said so... > >IE everywhere that I now say tree->something such as: > >tree->node_count++; > >could be replaced by a non-pointer: > >node_count++; > >It doesn't cost 5%... I have spoken to several commercial programmers and we all had similar results. Such an optimization (just for single cpu) will save 5-10%. Most claim 10%. Whether it's 4 or 5 or 6% is irrelevant. You just compare apples to petatoes.
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