"Invariant RDTSC" has been the norm for a long time now (identifiable by a CPUID feature bit) and it doesn't vary with power states or dynamic frequency. Which means it's just a lightweight, high precision timer at this point. In the Pentium 4 era you had a weaker guarantee called "Constant RDTSC" which could stop ticking in certain low power states.
Anyway, invariant RDTSC's tick rate is completely separate from the core clock. So the main issue you have to worry about with invariant RDTSC is having your process unscheduled or having ticks "stolen" by interrupts (which includes firmware invisible to the kernel or hypervisor).
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"Invariant RDTSC" has been the norm for a long time now (identifiable by a CPUID feature bit) and it doesn't vary with power states or dynamic frequency. Which means it's just a lightweight, high precision timer at this point. In the Pentium 4 era you had a weaker guarantee called "Constant RDTSC" which could stop ticking in certain low power states.
Anyway, invariant RDTSC's tick rate is completely separate from the core clock. So the main issue you have to worry about with invariant RDTSC is having your process unscheduled or having ticks "stolen" by interrupts (which includes firmware invisible to the kernel or hypervisor).