I can force it to use both CPUs now, but even with 200% utilization it is 2s slower to run this stupid ubenchmark than on 1 CPU without threads.
Just a vague guess, but the multiprocessor GIMP pixel work scheduler might* farm alternating tiles to alternating CPUs. These are reasonably likely to have been allocated together and thus sit close together in memory, causing memory contention between CPUs.
--Adam * I haven't looked at it. -- Adam D. Moss - adam@xxxxxxxx
