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Latest GNU version -- CPU % & multithreading

Posted By: Michael Petch
Date: Saturday, 23 May 2009, at 5:52 p.m.

In Response To: Latest GNU version -- CPU % & multithreading (Jason Lee)

The windows builds have been cleaned up and built properly compared to earlier releases. Most of the windows specific anomalies have disappeared over the past couple of months. In many cases "how" the windows product was built (optimization settings etc) lead to varying results.

The GnuBG team is *considering* removing the single threaded code base to simpify things overall. You will still be able to run on single processor systems by selecting one thread but there would be a bit of overhead since some threading specific code will still be executed. This is a future consideration, but it underscores that the developers believe that GnuBG's multithreaded implementation is mature enough for this type of consideration.

With regards to the 60% usage with 1 Eval thread (I assume you have 2 processors) - this is possible. In general the single threaded version of Gnubg uses multiple threads. On Windows there are generally 3-4 "non-eval threads" created by Gnubg (directly or indirectly). Underneath the GUI usually creates its own thread for better user interface performance. GnuBG doesn't consider this when you select "Eval Threads". "Eval Threads" only applies to the threads used to do an evaluation, not those created for GUI or other low level windows tasks.

One other possibility is that your processor is also taking advantage of some capabilities to parallelize instructions in a single thread on the fly, and run them on separate cores. So a single threaded applications can run slightly faster on a multi core system by vitue of the processors internal multicore and parallel processing features.

If you have multiple cores I recommend (for maximum performance) that one try to set the number of Eval Threads to the number of cores on the system. This allows Gnubg to split up the evaluation tasks across multiple threads which can then be run on different cores.

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