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By default OpenMP directive:
opm_get_num_threads gives number of threads equivalent to processors/cores.
I have an 8 core machine, so it gives me 8 threads. Is that the maximum? Can I get more threads than 8, if I deliberately specify more than 8?
Thanks
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Threads typically wait until the os allows them to run. OSs typically have a scheduler that schedules various threads to run as resources are available. Also, it must be taken into account that in a modern operating system, there are many, many threads running, way more than cores.
Cores increase the amount of work accomplished at a time, whereas threads improve throughput, computational speed-up. Cores is an actual hardware component whereas thread is a virtual component that manages the tasks. Cores use content switching while threads use multiple CPUs for operating numerous processes.
Threads refer to the highest level of code executed by a processor, so with many threads, your CPU can handle several tasks at the same time. All CPUs have active threads, and every process performed on your computer has at least a single thread.
First of all,you can't run more than 8 threads. Second,resort to nested parallelism if nothing else works as openmp has to improve a lot in this aspect.
You can set as many threads as you want with:
int threads = 16;
omp_set_num_threads(threads);
http://msdn.microsoft.com/en-US/library/e16bady3%28v=vs.80%29
But be sure you are aware of the drawbacks of using more threads than there are logical cores in the system.
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