- If the max CPUID leaf is >= 0x15, take TSC value from CPUID. Some processors
can take TSC/core crystal clock ratio but core crystal clock frequency
can't be taken. Intel SDM give us the values for some processors.
- It also required to change lapic_per_second to make LAPIC timer correctly.
- Add new file x86/x86/identcpu_subr.c to share common subroutines between
kernel and userland. Some code in x86/x86/identcpu.c and cpuctl/arch/i386.c
will be moved to this file in future.
- Add comment to clarify.
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