NdisGetCurrentProcessorCounts function

Description

The NdisGetCurrentProcessorCounts function returns counts for the current processor that a driver can use to determine CPU usage for a particular time interval.

Parameters

pIdleCount [out]

A pointer to a caller-supplied variable in which this function returns the cumulative idle time for the processor since the system was booted.

pKernelAndUser [out]

A pointer to a caller-supplied variable in which this function returns the cumulative processing time (kernel-mode time plus user-mode time) for the processor since the system was booted.

pIndex [out]

A pointer to a caller-supplied variable in which this function returns a zero-based index that identifies the processor within the computer.

Remarks

NdisGetCurrentProcessorCounts returns idle and CPU-usage counts that the caller can use to determine CPU usage for the current processor. The CPU utilization value indicates how loaded the CPU was since the immediately preceding call to this function. If the CPU was heavily loaded, such a driver can change how it handles certain operations to improve driver performance.

Note Estimating processor usage is difficult, and drivers generally don't do it. Note that, even if you have an accurate estimate of processor usage, there are other factors that you need to take into account, such as what is causing the load on the CPU – and how important that particular load might be.

A driver might call NdisGetCurrentProcessorCounts periodically within a timer function. The driver can use the following calculation to determine the CPU usage for a multiple of the timer interval:

CpuUsage = 100-100*(Idle - Idle[n])/(KernelAndUser - KernelAndUser[n]);

where:

• CpuUsage is CPU usage as a percentage of the total interval time
• Idle is the IdleCount value returned by the most recent call to NdisGetCurrentProcessorCounts
• Idle[n] is an IdleCount value returned by a previous call, stored as the nth element in an array
• KernelandUser is the KernelAndUser value returned by the most recent call to NdisGetCurrentProcessorCounts
• KernelandUser[n] is the KernelandUser value returned by a previous call, stored as the nth element in an array