Author: Robert Hyatt
Date: 07:29:07 07/16/03
Go up one level in this thread
On July 16, 2003 at 00:44:34, Keith Evans wrote: >On July 16, 2003 at 00:29:43, Robert Hyatt wrote: > >>On July 16, 2003 at 00:05:29, Keith Evans wrote: >> >>>On July 15, 2003 at 23:35:30, Robert Hyatt wrote: >>> >>>>On July 15, 2003 at 23:05:37, Vincent Diepeveen wrote: >>>> >>>>> >>>>> >>>>>Now i can disproof again the 130ns figure that Bob keeps giving here for dual >>>>>machines and something even faster than that for single cpu (up to 60ns or >>>>>something). Then i'm sure he'll be modifying soon his statement something like >>>>>to "that it is not interesting to know the time of a hashtable lookup, because >>>>>that is not interesting to know; instead the only scientific intersting thing is >>>>>to know is how much bandwidth a machine can actually achieve". >>>>> >>>> >>>> >>>>What is _interesting_ is the fact that you are incapable of even recalling >>>>the numbers I posted. >>>> >>>>to wit: >>>> >>>>dual xeon 2.8ghz, 400mhz FSB. 149ns latency >>>> >>>>PIII/750 laptop, SDRAM. 125ns. >>>> >>>>Aaron posted the 60+ ns numbers for his overclocked athlon. I assume his >>>>numbers are as accurate as mine since he _did_ run lm_bench, rather than >>>>something with potential bugs. >>>> >>>>I can post bandwidth numbers if you want, but that has nothing to do with >>>>latency, as those of us understanding architecture already know. >>>> >>> >>>Can you run lmbench and give the latency numbers for different stride sizes? >>>Then you could quote numbers from cache,... >>> >> >>Here's my laptop data. L1 seems to be 4 clocks. L2 9 clocks, memory >>at 130ns. This is a PIII/750mhs machine with SDRAM. I just ran it again >>to produce these numbers. >> >> >> >>Host OS Mhz L1 $ L2 $ Main mem Guesses >>--------- ------------- --- ---- ---- -------- ------- >>scrappy Linux 2.4.20 744 4.0370 9.4300 130.2 >> >>>In the lmbench paper they have a nice graph like this. >> >> >>Is the above what you want? > >I think that it's as close as you're going to get. The most important thing is >that 130 [ns] is the largest number. And wouldn't that be a little bit >pessimistic even for chess hash tables? I don't think so, although, in the case of crafty, the actual latency is about 1/3 of that, since I read three positions and you would ammortize the latency over those three positions rather than just over one.
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