Messages in this thread | | | Date | Sun, 31 Aug 2003 15:53:23 -0700 | From | Dan Kegel <> | Subject | Re: LMbench as gcc performance regression test? |
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Larry McVoy wrote: > Here is some background, pick a benchmark and play with it and see if > you can convince yourself of anything. The basic idea is to run the > benchmark TRIES times for $ENOUGH milliseconds. TRIES is set to an odd > number in bench.h because we sort the results and take the midpoint and > print that as the result.
It seems lat_pipe never does any median smoothing; it always sets TRIES to 1. However, at least on the fairly quiet embedded system I'm testing on, smoothing samples taken within a single run wouldn't make a huge difference. Any smoothing you get with that would be swamped by the fact that lat_pipe's result has a bimodal distribution only one of whose peaks shows up in any one run. This sure sounds like the kind of thing page coloring is supposed to solve; has anyone observed page coloring improving the repeatability of the lat_pipe benchmark?
(There's no median smoothing in lat_pipe.c, I think, because it passes a value >= 1000000 as the 2nd arg of BENCH: BENCH(doit(p2[0], p1[1]), SHORT); BENCH computes the number of samples to take the median of as __N = (get_enough(1000000) <= 100000) ? TRIES : 1; get_enough() will always return at least what it is passed, thus __N will always be 1. It sure was whenever I printed it out, too. This seems to be the case for the following tests: bw_pipe bw_tcp bw_unix lat_fcntl lat_fifo lat_pipe lat_rpc lat_tcp lat_udp lat_unix) - Dan
-- Dan Kegel http://www.kegel.com http://counter.li.org/cgi-bin/runscript/display-person.cgi?user=78045
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