Author: Keith Evans
Date: 09:58:33 07/16/03
Go up one level in this thread
On July 16, 2003 at 10:29:07, Robert Hyatt wrote: >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. That's what I meant - the 130 [ns] number is pessimistic given that you really have an average latency 1/3 of that.
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