[Bug-gnubg] Fwd: Optimizing thread settings

[Ian Shaw]

Hi,

I'd like to understand how to optimize the "set threads n" setting for multi-processor computers.

I've run the gnubg calibration speed test on a system with 2 x Xeon X3450 2.67 GHz CPUs. The CPU is listed as 4 cores, 8 threads.

Threads   eval/sec
 1          70k
 2         150k
 4         218k
 8         266k (as recommended by the tooltip)
16         326k
24         342k
32         355k
40         362k
48         366k (the maximum configurable)

For comparison, my P4 2 GHz single core desktop gives 25k eval/sec for any number of threads.

My Core2 Duo T8100 2.1 GHz laptop gives:

Threads   eval/sec
 1          51k
 2          98k (as recommended by the tooltip)
 4          98k

So, whereas the older PCs get no benefit from configuring more threads than physically available, the new processor can get improved performance by using more cores than physically present. If I'd just entered the recommended setting, I'd have chucked away a 37% performance benefit.

Some questions:

1) How is it possible to get extra performance by using more threads than the computer has?
2) Is there a reason for the 48-thread limit? My performance gain was tailing off, but there might have been more available. I notice that 6-core, 12-thread processors are now available.
3) Should the tooltip be changed?


Cheers,
Ian Shaw