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Both AMD and Intel CPUs support the RDTSCP instruction.
'cpuctl indentify 0'
prints it in the features3 line.
The differences between RDTSC and RDTSCP are:
- RDTSCP is a serializing instruction
- RDTSCP additionally loads the lower 32bits
of MSR_TSC_AUX into ecx register.
The MSR_TSC_AUX (0xc0000103) is read-write
for the OS and can be filled with anything
meaningful to the OS (i.e. processor ID).
The upper 32bits are reserved.
The MSR exists for each CPU-core.
The question is: What useful information
can NetBSD store into MSR_TSC_AUX ?
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