Table of Contents

CPU Load Calculation

Note

This calculation is available in all main connector ranges:

  • Microsoft Platform connector range 1.1.3.x
  • Microsoft Platform connector range 6.0.0.x
  • Microsoft Platform connector range 7.0.0.x

Metrics

The following metrics are used to calculate the CPU load:

Timestamp_Sys100NS

The timestamp value in 100 nanoseconds units. Available in Win32_PerfRawData_PerfOS_Processor.

Percent Processor Time

The percentage of elapsed time that the processor spends executing a non-idle thread. This value is calculated by measuring the percentage of time the processor spends executing the idle thread and subtracting that value from 100%.

Key characteristics:

  • Each processor has an idle thread that consumes cycles when no other threads are ready to run.
  • This counter is the primary indicator of processor activity.
  • This displays the average percentage of busy time observed during the sample interval.
Important

The accounting calculation of whether the processor is idle is performed at an internal sampling interval of the system clock (10 ns). On modern fast processors, PercentProcessorTime can underestimate processor utilization because the processor may spend significant time servicing threads between system clock sampling intervals. Workload-based timer applications are more likely to be measured inaccurately, as timers are signaled just after the sample is taken.

The counting type for this property is PERF_100NSEC_TIMER_INV, which measures the percentage of time the counter is not in use, in 100 nanosecond units. This is essentially an inverse timer that tracks idle time rather than busy time.

WMI Query:

SELECT PercentProcessorTime, Timestamp_Sys100NS, Name FROM Win32_PerfRawData_PerfOS_Processor

This query returns the percent processor time for each logical processor available in the server. In addition, it returns an extra entry that provides the total processor load (_Total).

The performance counter is based on idle time, not directly on busy time. Windows tracks how long the processor spends in the idle thread as follows:

  • Raw counter values (\(N_{1}\), \(N_{2}\)) represent cumulative idle time ticks at two sampling points of Percent Processor Time.

    \[ \Delta\,\,\text{Percent Processor Time}= N_{2}-N_{1} \]

  • Raw base values (\(D_{1}\), \(D_{2}\)) represent cumulative total ticks at those points (from Timestamp_Sys100NS).

    \[ \Delta\,\,\text{Timeticks} = D_{2}-D_{1} \]

Since the counter type identifies it as inverse, the CPU load is calculated as follows (based on Using Raw Performance Data Classes):

\[ \text{CPU Load}=100\times\left(1-\frac{\Delta\,\,\text{Percent Processor Time}}{\Delta\,\,\text{Timeticks}}\right) \]

Characteristics of the CPU load calculation

References

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