applecpu

Great post - glad some of that code has been useful! If it's of interest, these performance events (and the whitelist for this API), are described by Apple at https://github.com/apple/darwin-xnu/blob/main/osfmk/arm64/kp... Instruments.app is the official way to access performance counters. I believe it can use a few more (non-whitelisted) events, which are described in /usr/share/kpep/a14.plist - I couldn't figure out how to hijack the single-consumer API that I think it's using. (Edit: it seems it just shows non-whitelisted events in the GUI, but doesn't let me use them.) (And, for my own measurements, I use a kernel module to bypass the whitelist, which is even more likely to blow up the computer, and definitely not recommended: https://github.com/dougallj/applecpu/tree/main/timer-hacks )

There has been an update: >… The M1 seems to use something other than an entirely conventional reorder buffer, which complicates measurements a bit. So these may or may not be accurate. (This paragraph previously said "it seems to use something along the lines of a validation buffer". I think the VB hypothesis has since been disproven. Various attempts to measure ROB size have yielded values 623, 853, and 2295 (see the previous link). My uninformed hypothesis is that this may imply a kind of distributed reorder buffer, where only structures that need to know about a given operation track them, and/or some kind of out-of-order retirement.) https://github.com/dougallj/applecpu/commit/dc3c220f58f428b5...