run time with new quad-core

[deeppow]

Have a code that has been parallelized using Openmp. Compiling with auto-parallelization on plus using multi-thread library. Baselined a typical calculation as a reference prior to changing from my E6600 to a new Q6600. The run time has ~ doubled with my change from the dual-core to the quad. I'm using calls to CPU_TIME to do timing. While I understand that a change from 2 cores to 4 cores might hurt performance (instead of improving it), the ~doubling of the displayed run time is suspicious.

Any suggestions? Am I missing something obvious?

Thanks for any assistance!

[Steven_L_Intel1]

You're not measuring run time, you're measuring all the CPU time in the four threads together. Try measuring elapsed time (using SYSTEM_CLOCK perhaps) and see if things look better.

It could be you have a lot of contention across the threads. Intel Thread Profiler can show you that.

[deeppow]

Yes, timing using system_clock makes much better sense. Thanks