Benchmark code is in the post! The trick is to limit the number of SHLX instructions before you re-initialize RCX. Doing it every 10,000 keeps it fresh enough

Benchmark code is in the post! The trick is to limit the number of SHLX instructions before you re-initialize RCX. Doing it every 10,000 keeps it fresh enough. I didn't have to disable preemption or anything, perf shows 0 context switches and only ~50 page faults (probably all at startup).