Synchronizing time domain signals in computing system using phase frequency slope value of cross power spectral density

1. A method for accurately synchronizing time-domain signals related to the operation of a computer system, comprising:

receiving a first time-domain signal associated with a first system variable and a second time-domain signal associated with a second system variable from the computer system, wherein the first and second time-domain signals include signals associated with physical parameters gathered from physical sensors in the computer system;

transforming the first and the second time-domain signals into a first frequency-domain signal and a second frequency-domain signal, respectively;

computing a cross-power-spectral-density (CPSD) between the first and second frequency-domain signals to obtain a phase angle versus frequency graph between the two frequency-domain signals;

extracting the slope of the phase angle versus frequency graph; and

using the value of the slope to synchronize the first time-domain signal and the second time-domain signal.

2. The method of claim 1 ,

wherein the value of the slope of the phase versus frequency graph is proportional to the phase difference between the first and the second time-domain signals; and

wherein the sign of the slope determines a lead or lag relationship between the first and the second time-domain signals.

3. The method of claim 1 ,

wherein the first time-domain signal is generated from a first sampled signal and the second time-domain signal is generated from a second sampled signal; and

wherein a sampling rate of the first sampled signal is different from a sampling rate of the second sampled signal.

4. The method of claim 1 , wherein prior to transforming the first and the second time-domain signals, the method further comprises re-sampling each of the time-domain signals so that a sampling rate of the first time-domain signal is substantially equal to a sampling rate of the second time-domain signal.

5. The method of claim 1 , wherein the first time-domain signal is measured by a first measurement system having a first clock and the second time-domain signal is measured by a second measurement system having a second clock.

6. The method of claim 1 , wherein using the value of the slope to synchronize the two time-domain signals involves iteratively adjusting a phase difference between the two time-domain signals until the slope of the phase angle versus frequency graph is substantially equal to zero.

7. The method of claim 1 , wherein:

the first system variable includes a physical sensor variable and a software performance variable; and

the second system variable includes a physical sensor variable and a software performance variable.

8. The method of claim 7 ,

wherein the physical sensor variable includes one of: a CPU power, and a CPU temperature; and

wherein the software performance variable includes one of: a utilization metric of the CPU, and a throughput of the computer system.

9. The method of claim 1 , wherein the first and the second time-domain signals are used to generate an accurate power-versus-utilization graph of the computer system.

10. A computer-readable storage medium storing instructions that when executed by a computer cause the computer to perform a method for accurately synchronizing time-domain signals related to the operation of a computer system, comprising:

receiving a first time-domain signal associated with a first system variable and a second time-domain signal associated with a second system variable from the computer system, wherein the first and second time-domain signals include signals associated with physical parameters gathered from physical sensors in the computer system;

transforming the first and the second time-domain signals into a first frequency-domain signal and a second frequency-domain signal, respectively;

computing a cross-power-spectral-density (CPSD) between the first and second frequency-domain signals to obtain a phase angle versus frequency graph between the two frequency-domain signals;

extracting the slope of the phase angle versus frequency graph; and

using the value of the slope to synchronize the first time-domain signal and the second time-domain signal.

11. The computer-readable storage medium of claim 10 ,

wherein the value of the slope of the phase versus frequency graph is proportional to the phase difference between the first and the second time-domain signals; and

wherein the sign of the slope determines a lead or lag relationship between the first and the second time-domain signals.

12. The computer-readable storage medium of claim 10 ,

wherein the first time-domain signal is generated from a first sampled signal and the second time-domain signal is generated from a second sampled signal; and

wherein a sampling rate of the first sampled signal is different from a sampling rate of the second sampled signal.

13. The computer-readable storage medium of claim 10 , wherein prior to transforming the first and the second time-domain signals, the method further comprises re-sampling each of the time-domain signals so that a sampling rate of the first time-domain signal is substantially equal to a sampling rate of the second time-domain signal.

14. The computer-readable storage medium of claim 10 , wherein the first time-domain signal is measured by a first measurement system having a first clock and the second time-domain signal is measured by a second measurement system having a second clock.

15. The computer-readable storage medium of claim 10 , wherein using the value of the slope to synchronize the two time-domain signals involves iteratively adjusting a phase difference between the two time-domain signals until the slope of the phase angle versus frequency graph is substantially equal to zero.

16. The computer-readable storage medium of claim 10 , wherein:

the first system variable includes a physical sensor variable and a software performance variable; and

the second system variable includes a physical sensor variable and a software performance variable.

17. The computer-readable storage medium of claim 16 ,

wherein the physical sensor variable includes one of: a CPU power, and a CPU temperature; and

wherein the software performance variable includes one of: a utilization metric of the CPU, and a throughput of the computer system.

18. The computer-readable storage medium of claim 10 , wherein the first and the second time-domain signals are used to generate an accurate power-versus-utilization graph of the computer system.

19. An apparatus that accurately synchronizes time-domain signals related to the operation of a computer system, comprising:

a receiving mechanism configured to receive a first time-domain signal associated with a first system variable and a second time-domain signal associated with a second system variable from the computer system, wherein the first and second time-domain signals include signals associated with physical parameters gathered from physical sensors in the computer system;

a transformation mechanism configured to transform the first and the second time-domain signals into a first frequency-domain signal and a second frequency-domain signal, respectively;

a computing mechanism configured to compute a cross-power-spectral-density (CPSD) between the first and second frequency-domain signals to obtain a phase angle versus frequency graph between the two frequency-domain signals;

an extraction mechanism configured to extract the slope of the phase angle versus frequency graph; and

a synchronization mechanism configured to use the value of the slope to synchronize the first time-domain signal and the second time-domain signal.

20. The apparatus of claim 19 ,

wherein the value of the slope of the phase versus frequency graph is proportional to the phase difference between the first and the second time-domain signals; and

wherein the sign of the slope determines a lead or lag relationship between the first and the second time-domain signals.