[markh83]

Hi.. I've just recently got access to a quite big cluster.. Containing a total of about 1440 cores.. But I've noticed, that more cores do not always increase the calculation speed.. As an example.. I have a grid, containing 106250 cells.. I've tried three different runs, one on 100 cores, one on 20 cores and one on an other workstation with just 1 core.. The estimated calculation speeds is:
1 core: 163 hours
20 cores: 10 hours
100 cores: 18 hours


I've also noticed, that the seems to be an acceleration in simulation speed from the start, eg if you make an estimate just when the calculations have begun, it will be higher than an estimate after an hour.
The simulations is to simulate 500 seconds, and the the simulations has so far reached (They were not started at the same time):
1 core: 450 secs simulated
20 cores: 19 secs simulated
100 cores: 23 secs simulated

So my conclussion is, that since the 20 cores seems to be faster than both 100 cores and 1 core, there must be an optimum number of cores to use..

Is there any literature available on this subject, or does any of you guys have a rule of thumb to use, as to how many cores should be utilized?