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Use CPUID leaf 0x15 to get TSC frequency when the calibration is

Description

Use CPUID leaf 0x15 to get TSC frequency when the calibration is
disabled.

Intel finally added this information, which allows us to not parse CPU
identification string looking for the nominal frequency. The leaf is
present e.g. on Appolo Lake Atom CPUs. It is only used if the TSC
calibration is disabled by user.

Also, report the TSC frequency in bootverbose mode always, regardless
of the way it was obtained.

Sponsored by: The FreeBSD Foundation
MFC after: 1 week

Details

Provenance
kibAuthored on
Parents
rS333001: bsdgrep(1): Sneak in some man page updates
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