LARGE_INTEGER
KeQueryPerformanceCounter(
IN PLARGE_INTEGER PerformanceFrequency /* optional */
);
KeQueryPerformanceCounter provides the finest grained running count available in the system.
Parameters
PerformanceFrequency
Specifies an optional pointer to a variable that is to receive the performance counter frequency.
Return Value
KeQueryPerformanceCounter returns the performance counter value in hertz.
Comments
KeQueryPerformanceCounter always returns a 64-bit integer representing the number of ticks per second. Accumulating the count begins when the system is booted. The count is in ticks; the frequency is reported by PerformanceFrequency if this optional parameter is supplied.
The resolution of the timer used to accumulate the current count can be obtained by specifying PerformanceFrequency. For example, if the returned PerformanceFrequency is 2 million, each tick is 1/2 millionth of a second. Each 1/x millionth increment of the count corresponds to one second of elapsed time.
KeQueryPerformanceCounter is intended for time stamping packets or for computing performance and capacity measurements. It is not intended for measuring elapsed time, for computing stalls or waits, or for iterations.
Use this routine sparingly, calling it as infrequently as possible. Depending on the platform, KeQueryPerformanceCounter can disable system-wide interrupts for a minimal interval. Consequently, calling this routine frequently or repeatedly, as in an iteration, defeats its purpose of returning very fine-grained, running time-stamp information. Calling this routine too frequently can degrade I/O performance for the calling driver and for the system as a whole.
Callers of KeQueryPerformanceCounter can be running at any IRQL.
See Also