KeQueryInterruptTimePrecise function (wdm.h)

Article
02/25/2022

The KeQueryInterruptTimePrecise routine returns the current value of the system interrupt time count, with accuracy to within a microsecond.

Syntax

ULONG64 KeQueryInterruptTimePrecise(
  [out] PULONG64 QpcTimeStamp
);

Parameters

[out] QpcTimeStamp

A pointer to a ULONG64 variable into which the routine writes the performance counter value used to interpolate the return value.

Return value

The current interrupt-time count in 100-nanosecond units.

Remarks

KeQueryInterruptTimePrecise returns the system's current interrupt time, which is the amount of time since the operating system was last started. KeQueryInterruptTimePrecise is similar to the KeQueryInterruptTime routine, but is more precise.

The interrupt time reported by KeQueryInterruptTime is based on the latest tick of the system clock timer. The clock timer is the hardware timer that periodically generates interrupts for the system clock. The uniform period between clock timer interrupts is referred to as a system clock tick, and is typically in the range of 500 microseconds to 15.625 milliseconds, depending on the hardware platform. The interrupt time value retrieved by KeQueryInterruptTime is accurate within a system clock tick.

To provide an interrupt time value that is more precise than that of KeQueryInterruptTime, KeQueryInterruptTimePrecise uses the system performance counter to measure the time elapsed since the last clock timer interrupt, and adds this time to the interrupt time associated with the latest clock time. The interrupt time reported by KeQueryInterruptTimePrecise is accurate to within a microsecond.

On some hardware platforms, a KeQueryInterruptTimePrecise call might be slower than a KeQueryInterruptTime call. The reason is that KeQueryInterruptTimePrecise reads the performance counter, which can introduce an additional delay. For more information, see KeQueryPerformanceCounter.

Call the KeQueryTimeIncrement routine to determine the size of a system clock tick.

Precise interrupt time can be used to measure very fine-grained durations while the system is running because operations that set or reset the system time have no effect on the system interrupt time count.

However, power-management state changes do affect the system interrupt time count. Maintenance of the interrupt time count is suspended during system sleep states. When a subsequent wake state transition occurs, the system adds a "bias" value to the interrupt time count to compensate for the estimated duration of such a sleep state. The interrupt time count that is returned by KeQueryInterruptTimePrecise includes this bias value. To obtain an unbiased interrupt time count, use the KeQueryUnbiasedInterruptTime. A precise version of the unbiased interrupt time count is not currently available.

Requirements

Requirement	Value
Minimum supported client	Available starting with Windows 8.1.
Target Platform	Universal
Header	wdm.h (include Wdm.h, Ntddk.h, Ntifs.h)
Library	NtosKrnl.lib
DLL	NtosKrnl.exe
IRQL	Any level