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Best Threads Per Core with Intel Xeon Phi

“When designing an application that contains many threads and less cores than threads, it is important to understand what is the optimal number of threads that should be assigned to a core. This value should be parameterized, in order to easily run tests to determine which is the optimum value for a given machine. One thread per core on the Intel Xeon Phi processor will give the highest performance per thread. When the number of threads per core is set at two or four, the individual thread performance may be lower, but the aggregate performance will be greater.”

Programming Many Tasks for Many Cores

“Tasks keep the CPUs busy. When a core is working, rather than waiting for work to be sent to it, the application progresses towards it conclusion. A caveat to all of this is to remember that tasking and threading models remain on the system it was created on. Tasks that use a shared memory space only work within the shared memory segment that the processing cores can get to. Shared memory on the CPU side of the system is separate from the shared memory on the coprocessor. The threads created will remain on the part of the system where it started.”

Application Performance & Power Consumption on Intel Xeon Phi

“While new technology will be developed that reduces the power per operation needed, in today’s environments it is important to understand how an application affects power usage. For modern applications that have been optimized to take advantage of both the Intel Xeon CPU and the Intel Xeon Phi coprocessor, the hardware mentioned does include various power states, which can minimize the power consumption when idle.”

OpenMP and SIMD Instructions on Intel Xeon Phi

“Vector instruction sets have progressed over time, and it important to use the most appropriate vector instruction set when running on specific hardware. The OpenMP SIMD directive allows the developer to explicitly tell the compiler to vectorize a loop. In this case, human intervention will override the compilers sense of dependencies, but that is OK if the developer knows their application well.”