different behavior when using different number of multicoring workers

Question

I am playing around a bit with my program (trying to multicore a few parts) and I\'ve noticed the \"CPU history\" looks a bit different, depend on how many workers I start.

Answer 1

This is classic behaviour on a quad-core with hyperthreading. R doesn't gain with hyperthreading, as it uses often the complete core for the calculations. Thus, if one physical processor makes 2 logical ones, the processor has to switch continuously between both threads, which explains the patterns.

For R, I put off the hyperthreading on my computer. It just doesn't help, in contrary. When working with only one thread as R does normally, you lose capacity (max is 12.5% instead of 25%).