NdisGetCurrentProcessorCounts function (ndis.h)

Article
04/18/2022

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

Syntax

void NdisGetCurrentProcessorCounts(
  [out] PULONG pIdleCount,
  [out] PULONG pKernelAndUser,
  [out] PULONG pIndex
);

Parameters

[out] pIdleCount

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

[out] pKernelAndUser

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.

[out] pIndex

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

Return value

None

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

Requirements

Requirement	Value
Minimum supported client	Supported for NDIS 6.0 and later drivers in Windows Vista and later. Supported for NDIS 5.1 drivers (see NdisGetCurrentProcessorCounts (NDIS 5.1)) in Windows XP and later.
Target Platform	Universal
Header	ndis.h (include Ndis.h)
Library	Ndis.lib
IRQL	<= DISPATCH_LEVEL
DDI compliance rules	Irql_Miscellaneous_Function(ndis)

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