CHA latency conversion #5
Description
- run/colloid/tpp/colloid-mon/colloid-mon.c converts TOR_OCC/TOR_INSERT into latency via (cha_delta_tsc * 1000 / frequency) / cha_clockticks, but frequency is hard-coded to 2200 MHz.
- In our setup we change uncore clocks through run/bc-urand/modify-uncore-freq.sh (/sys/devices/system/cpu/intel_uncore_frequency/...), so CHA0/CHA1 no longer run at 2.2 GHz and the latency comparison becomes wrong. Besides, the control mechanism for the uncore frequency on skylake inherently has some latency, and it's impossible to truly fix the Uncore frequency (see https://arxiv.org/abs/1905.12468).
Fix idea: rewrite the logic to use relative speed between CHA0 and CHA1 (so the decision depends only on ratios, not an absolute MHz constant).