Software Tuning, Performance Optimization & Platform Monitoring
Discussion around monitoring and software tuning methodologies, Performance Monitoring Unit (PMU) of Intel microprocessors, and platform monitoring

TSC frequency variations with temperature

Corey_R_
Beginner
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Given an invariant TSC on a relatively recent (Ivy Bridge+) chip, to what extent is the frequency the TSC is incremented at influenced by temperature? Does anyone have any measurements of this?
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McCalpinJohn
Black Belt
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The invariant TSC should only change frequency if the 100 MHz reference clock changes frequency.  Since this is generated outside the processor, the processor temperature should not have a direct impact.  (There will be an indirect impact if the processor heats up the entire motherboard, of course.)

The amount of temperature-induced drift of this reference clock will depend on the quality of the implementation.    For a clock that is going to be used for the PCIe interface, the PCIe standard specifies that the clock must be accurate to within 300ppm, so the worst case allowable would be +/- 0.03%.

If I am reading the datasheets correctly, clock generators for Intel processors are typically specified to have an accuracy of no worse than 100 ppm, or +/- 0.01%.

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McCalpinJohn
Black Belt
356 Views

The invariant TSC should only change frequency if the 100 MHz reference clock changes frequency.  Since this is generated outside the processor, the processor temperature should not have a direct impact.  (There will be an indirect impact if the processor heats up the entire motherboard, of course.)

The amount of temperature-induced drift of this reference clock will depend on the quality of the implementation.    For a clock that is going to be used for the PCIe interface, the PCIe standard specifies that the clock must be accurate to within 300ppm, so the worst case allowable would be +/- 0.03%.

If I am reading the datasheets correctly, clock generators for Intel processors are typically specified to have an accuracy of no worse than 100 ppm, or +/- 0.01%.

Corey_R_
Beginner
355 Views

Ok, thanks John!

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