[erlang-questions] VM not able to use available cores

Paul Brown <>
Sun Jan 20 06:32:45 CET 2008


EQ --

On a somewhat random lark, I decided to fire up the "big.erl"  
exerciser on a new box (8 cores, Xeon, Mac OS 10.5, R12B) that  
replaced an old box (4 cores, PPC G5, Mac OS 10.4, R11B), and the  
initial returns were surprising -- the 8-core box exhibited more or  
less equivalent performance to the 4-core...  (Pretty graphs, links to  
big.erl source I used, etc., are here - http://mult.ifario.us/p/use-the-cores-erl

A little more digging, and it turned out that the VM was only able to  
use the equivalent of 3 cores worth of CPU cycles, no matter how many  
schedulers I ran from the command line.  Two VMs does a reasonable job  
of using all 8 cores worth of cycles, but I'm left with the question  
of why a single VM couldn't use more cores.

Any thoughts?

-- Paul



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