4 ms·

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

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/kpc.c 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 https://github.com/dougallj/applecpu/tree/main/timer-hacks )

kragen 6y ago
Interesting! Do you need Apple's permission to write a kernel module? Have you tried running this kind of instrumentation on Linux on M1?
- dougall 6y ago
  I don't really understand the kernel module process/policy - it was a lot of trying random things and seeing what worked. But I think you shouldn't need permission, as long as you're building it and running it on your own machine. But I do have an Apple developer account that costs money to let you develop on iOS, so that might have been a factor. You do need to disable some security features to run kernel modules. I'd rather be running this kind of instrumentation on Linux (or without a kernel, e.g. using m1n1), but I haven't set that up yet. (It'd be nice to lock the CPU to a frequency, and pin threads to cores, etc.)
  - kragen 6y ago
    Thank you!