Author: Robert Hyatt
Date: 15:26:09 09/03/02
Go up one level in this thread
On September 03, 2002 at 17:44:26, martin fierz wrote: >On September 03, 2002 at 16:26:33, Robert Hyatt wrote: > >>On September 03, 2002 at 15:50:45, Matthew Hull wrote: >> >>>On September 03, 2002 at 15:42:08, Gian-Carlo Pascutto wrote: >>> >>>>http://sjeng.sourceforge.net/ftp/hyatt1.png >>>> >>>>I will try to upload the full article as soon as I can. >>>> >>>>-- >>>>GCP >>> >>>You've got to be kidding. When Vincent posts the numbers, he's got all these >>>trailing zeros. What's with that? >>> >>>It is Vincent that's faking numbers here, not Bob. Bob's numbers are just >>>rounded off. >>> >>>Vincent is the one emitting bogons here. >> >> >>If you didn't see my response elsewhere, this output was produced by a program >>I wrote to "eat" Cray Blitz log files. I did this for my dissertation as I >>produced tens of thousands of test position logs for that. >> >>I believe that it does something similar to what I do today, which means that >>anything between 1.71 and 1.8 is treated as 1.8, 1.81 to 1.9 is 1.9. > >that sure sounds like a bad thing to do! you should retain 2 digits, since >the interesting number is not the speedup (1.8, 1.9, whatever), but rather the >difference to 2. I don't use a "log eater" today. I generally run a set of positions, and get a time for one processor, then a time for 2 processors and divide the two by hand. I do round to one dec. place as the numbers are already very unstable, and going to more accuracy is really pointless... > so if you measure 1.91 or 1.99, you really measure 0.09 or >0.01, and obviously these two numbers are quite different. >also, if you really feel like rounding, you should do it in the normal sense, >like 1.750 - 1.849 -> 1.8. i don't believe a word of vincent's post, but always >rounding upwards is definitely making your data look better than it is, and >should be rejected by any reviewer or thesis advisor - if he knew you were doing >that :-). not that it makes a big difference of course - but for the 2-processor >case we are talking about a potential >10% error, which where it starts getting >significant. > >aloha > martin > or really 5% max? ie 1.9 to 1.99 is only 5% difference... >> I am >>not _certain_ as I don't have any of the old files left, they were all lost >>somewhere around 96-97. And I might be wrong. But something tells me that >>all this was integer values in Cray Blitz's logs, which means that it would >>be convenient to compute speedup = something + roundup and truncate it as it >>was all done in integers. >> >>however, I won't bet my life that I did that as the "log eater" was written in >>1987 while working on my dissertation. that is a _long_ time ago to remember >>some tiny detail inside the thing...
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