On Thu, Aug 9, 2012 at 11:14 AM, Petr Baudis <pa...@ucw.cz> wrote: > On Wed, Aug 08, 2012 at 09:08:47PM +0200, ds wrote: > > Hyperthreading does the trick, I have the experience it increases the > > performance by about 10%. I think this is due to waiting for RAM I/O or > > things like that.... > > Yes. With hyperthreading, performance per thread goes down > significantly, but total performance goes up by about 15%. In the > Pentium 4 era, hyperthreading did not usually pay off, but with i7, > its performance is much better. The basic idea is that there are two > instruction pipelines that share the same ALU and other processor units; > if one of the pipelines stalls (usually due to memory fetch), the other > can use the ALU in the meantime, or the two threads may use different > parts of the CPU altogether based on what the instructions do. > > 10-15%, really, that low? For my program (on an i7-3930K, going from 6 to 12 threads) it is more in the order of 40% extra simulations per second.
Erik
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