Author: Gerd Isenberg
Date: 14:14:45 07/15/03
Go up one level in this thread
On July 15, 2003 at 09:33:39, Robert Hyatt wrote: >On July 15, 2003 at 06:24:58, Vincent Diepeveen wrote: > >>On July 14, 2003 at 16:07:27, Robert Hyatt wrote: >> >>You measure the latency with those benches of sequential reads. > >No. lm-bench does _random_ reads and computes the _random-access_ >latency. > >Don't know why you have a problem grasping that. > > >>So already opened cache lines you can get data faster from than >>random reads to memory. > >That also makes no sense. Perhaps you mean "already opened memory >rows"? > > >> >>Random reads to memory are about 280 ns at single cpu P4 and about 400ns at dual >>P4s. > >No they aren't. > Bob, i found nothing wrong with Vincent's code. He does N-random hashreads and aggregates the time used. I thought about some factor 2 error - but found no one so far. Random Hashreads, like chess programs do. 1e9 random hash reads take 265 seconds (including ~60 seconds overhead) on my athlon-pc, however latency is defined. Any explanation? Any systematical error or assumption? What does lm-bench do, to measure latency? Regards, Gerd
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