Author: F. Huber
Date: 09:06:53 12/11/03
Hello! Since more than one week I´ve now a problem, which is really _strange_: Immediately after the release of my new ChestUCI version 3.0 I´ve got a response of some chess friends, that this new version is constantly slower than the last one (ver.2.8) by 8-10%. So I tested it myself on my new system (Pentium-IV 2.66), but I couldn´t confirm that - I got _absolutely identical_ solution times with this new version as with all previous ones! After some more tests we found out, that this 10% slowdown ONLY occurs on AMD-processors - NOT on Intel-CPUs !? And furthermore: the ´reason´ for this mysterious behaviour is not in my own ´ChestUCI´ (written in Borland Delphi), but in ´Chest´ itself (from Heiner Marxen), which is written in ANSI-C and modified by me (only some additional file output!) for better communication with my UCI-interface and compiled with MS-VC++ 6.0. So what has changed in ´Chest´ from 2.8 to 3.0? 1) I´ve included a few improvements and corrections from newer source files, which Heiner has sent me some time ago - but these were really _minor_ changes: absolut nothing that could explain a slowdown of Chest! (I´ve already emailed Heiner, but he also has no idea, how his small changes could have such an effect - and furthermore _only_ on AMD-CPUs) 2) I´ve added a few additional commands (file output) to Chest, but normally these are not even executed at all - only if you really request them by setting a special engine option. So also my own changes could not explain this slowdown. What has NOT changed? 1) I´ve _definitely_ NOT changed ANY compiler options! I tested this again and again, and I´m absolutely sure about this. Furthermore (since I´m not an expert in ´C´) I always compile(d) Chest with the compilers default settings (of course ´optimized for speed´, but that _is_ the default setting). 2) The size of the EXE-file (´WinChest.exe´) has NOT changed - not even a single byte! (no big surprise, since all changes were rather small) 3) And most important: as I mentioned above - the execution times on Intel-processors did NOT change at all !! Now, what have I tried? Within the last week I´ve exactly compared the new source code with the old one and searched for any possible errors - no success! Since I´ve no actual AMD-system I took my old one (AMD-K6/200MHz), which showed the same ´slowdown´ effect, made dozens of small changes in Chest (e.g. taking back some of the new changes) and recompiled it - no success! Once it seemed that I had found a solution (at least on my old K6 it was much faster again), but after having sent this new version to my friends, they said: "NOT faster, even slower!" - so this AMD-K6 seems not to be comparable with modern Athlons at all. And now I´ve really reached a point, where I have no further ideas, what else I could try. :-(( Since here are lots of experts, maybe someone will know a solution for this strange problem - or at least could give an explanation for this mysterious slowdown effect on AMD-CPUs. (What I´m really angry about is not this slowdown itself - because those AMD´s are anyway faster for chess than Intel´s - but the fact, that I don´t know ´WHY?´. And as long as this question is not answered, there´s still the bad feeling of ´maybe I´ve indeed made some error anywhere?´.) So hoping to get some ´good´ answers, ;-) my best regards, Franz.
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