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Oh, I get it! I'm not alone on a machine. The workaround would be to require 16 threads for the full test to keep the other threads idle (still no guarantee since the grid engine could give me 8 proc. on one core + 8 proc. on another...).So if you use 5 threads on 16 CPU machine, and 11 other CPUs are idle, you will be twice faster than when you use 5 CPUs and 11 other CPUs are used by someone else for other calculations. That's because Intel has very slow RAM access (contrary to AMD).
Did you try the "big cache" option? It allows you to skip RAM access and use the internal memory attached to the node. Remi said it can speed up "some" jobs a lot.Therefore making benchmarks on cluster makes little sense, you will get random results. (Unless you talk with everyone else to stop doing their calculations ;). I was doing calculations for several months, and I had 'htop' running of every node and I was noting down whether I am calculating alone, or if others are also using CPU. And those above were my observations.
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