Function tsc_frequency_khz 

pub fn tsc_frequency_khz() -> Option<u64>

Return the host’s default XCR0 mask (all supported features). Safe to call before init() : returns XCR0_X87 | XCR0_SSE if not yet initialized.

Try to read the TSC frequency from CPUID leaf 0x15 (Time Stamp Counter and Core Crystal Clock Information). Returns kHz, or None if not available.

This is the preferred method on Intel/AMD CPUs that support invariant TSC. Linux uses this as its primary TSC calibration source.