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- Apr 24, 2020
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How would each of the different cpu scheduling governors in Linux treat this?? Wonder how different each acts in ryzen vs intel of the same gen
OS doesn't care about anything discussed here. From the OS perspective, a hyperthreaded (or SMT) core looks like two cores (Core#1 and Core#2). The CPU "lies" to the operating system, but in a way that's well documented, so the OS can still figure out some details.
The decoder, the portion of the CPU that performs instruction scheduling, cares about the SMT vs Hyperthread vs (whatever) details.
Note that POWER9 is SMT-4 (4-threads per core) and SMT-8 (8-threads per core), depending on model. GPUs tend to be extremely SMT as well. The gist is that memory is so slow today that any memory-throttled multithreaded application will prefer SMT (ie: let all those pipelines and execution units operate on a 2nd thread entirely, while waiting on RAM).