Author: Gerd Isenberg
Date: 12:40:07 07/16/03
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On July 16, 2003 at 14:41:45, Dieter Buerssner wrote: >Just few comments about the thread. > >An interesting test would be, to do lmbench type linked list test with Vincent's >idea of real random access. I may try it out later. No PRNG calls will be >needed. The linked list will be initialized "pseudo randomly". In this case, it >would mean, that it will not be too close to real random, because in one cycle >every memory adress will be read once. (This could easily happen anyway, with >not so decent PRNGs). > >An perhaps interesting comment from lmbench source: > > > /* > * First create a list of pointers. > * > * This used to go forwards, we want to go backwards to try and defeat > * HP's fetch ahead. > * > * We really need to do a random pattern once we are doing one hit per > * page. > */ > >So, the authors did not seem too confident with the sequential like access? Or >did I misunderstand. Dieter, sorry for ignoring this in my post below. Yes i see, but to do exactly Vincent's sequence, calling RanrotA 100 million times in a loop, you need a rather huge list ;-) Gerd > >The PRNG Vincent uses is fine. I will do some tests on it. Lagged Fibonacci type >generators don't have problems with mod (often rand() uses a linear congruential >generator, which can have severe problem, especially when used with mod. Anyway, >for this sort of test, I think even very bad PRNGs would do well. There is no >way, the hardware can guess the access pattern. > >Regards, >Dieter
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