hw.cpufrequency does not exist on Apple Silicon (M1/M2)

[michaelsproul]

sysinfo currently uses the sysctl call hw.cpufrequency to get the CPU frequency on macOS.

sysinfo/src/apple/cpu.rs

Lines 128 to 134 in 463a88c

	libc::sysctlbyname(
	b"hw.cpufrequency\0".as_ptr() as *const c_char,
	&mut speed as *mut _ as _,
	&mut len,
	std::ptr::null_mut(),
	0,
	);

Due to trickery on Apple's part, this call returns nothing on new Apple Silicon parts like the M1.

This can be confirmed by trying to call sysinfo::Cpu::frequency on an Apple Silicon device, or by running sysctl in a terminal:

$ sysctl hw.cpufrequency
# no output
$ sudo sysctl hw.cpufrequency
# no output

It seems that Apple Silicon broke a lot of sysinfo-like libraries in other languages, and there are long threads discussing potential solutions, e.g. here: giampaolo/psutil#1892

The upshot of that thread seems to be that parsing the voltage-states1-sram value from ioreg -l is the most promising way of determining something vaguely like the CPU's nominal frequency. I haven't dug into how to call ioreg via a syscall, or how to parse its output.

[GuillaumeGomez]

Interesting, thanks for the information! I'd prefer to not run external binaries (because it's very slow) so I'll wait for a solution to appear before checking how this solution actually gets the information.

[GuillaumeGomez]

Seems like there is a PR open which gets this information: giampaolo/psutil#2222.