Time each CPU core spends in C0 power state

Any help figuring out how to do this would be great: How muc开发者_如何学JAVAh time each CPU core spent in the C0 power state over the past second.

This is for a mac app so Objective-C, cocoa and c are needed.

OS X doesn't have any APIs that expose the c-state of the CPU. However, it seems like you can do this using the MWAIT/MONITOR instructions on intel CPUs. Intel mentions that you can track C-state residency using this technique in section 14.4 of the reference manual:

Software should use CPUID to discover if a target processor supports the enumeration of MWAIT extensions. If CPUID.05H.ECX[Bit 0] = 1, the target processor supports MWAIT extensions and their enumeration (see Chapter 3, “Instruction Set Reference, A-M,” of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 2A).

If CPUID.05H.ECX[Bit 1] = 1, the target processor supports using interrupts as break-events for MWAIT, even when interrupts are disabled. Use this feature to measure C-state residency as follows:

Software can write to bit 0 in the MWAIT Extensions register (ECX) when issuing an MWAIT to enter into a processor-specific C-state or sub C-state.

When a processor comes out of an inactive C-state or sub C-state, software can read a timestamp before an interrupt service routine (ISR) is potentially executed.

You can find more info about the MWAIT instruction in the same manual. Good luck!

Intel's Reference Manual

For getting C0 percentage you should do the following:

Read following MSRs at start and end points of the period you measure:

0x3FC (core c3), 0x3FD (core c6), 0x3FE (core c7), 0x10 (tsc)

Then do the following calculation:

Cx_ticks = (c3_after - c3_before) + (c6_after - c6_before) + (c7_after - c7_before)
total_ticks = (tsc_after - tsc_before)
Cx_percentage = Cx_ticks/total_ticks
C0_percentage = 100% - Cx_percentage

You can find more information in this document (go to Vol. 3C 35-95)