Re: [Bug-gnubg] How many threads can gnubg (reliably) handle?

[Philippe Michel]

On Tue, 8 Sep 2009, Michael Petch wrote:

> I use 8 cores on Linux with no real issues.

I have run a few 4-ply match analyses (no rollout yet) on a 16 cores 
machine (CentOS 5, x86_64) with no obvious problems.

> Time will tell on how well Gnubg scales on a large number of processors.

On the other hand, analysis doesn't seem to scale well above 8 threads. It 
looks like moves are analysed one by one and after the opening and early 
middle game, even with a large move filter, some, then most of the threads 
are starved. 8 threads was about 7 times faster than 1, but 16 threads was 
merely 9 times faster.

I guess this won't be a problem for rollouts.

I tried large cache sizes as well and saw no problems up to 1G cache 
entries. Trying to set cache size to 2G fails silently. "set cache" uses 
ParseNumber() that cannot handle it and there may be other int variable 
involved as well. "show cache" from the CLI doesn't seem to work either.

For these match analyses, cache size above 256M didn't improve speed 
anyway.