function::read_stopwatch_us - Linux
Overview
The read_stopwatch_us()
function is part of the Linux Performance Application Programming Interface (PAPI) and is designed to retrieve the current elapsed time from a started stopwatch, expressed in microseconds. It is primarily used for performance measurement and to calculate elapsed time with high precision.
Syntax
#include <papi.h>
int read_stopwatch_us(int EventSet, long long *ns);
Options/Flags
- EventSet: An integer handle to the EventSet containing the stopwatch event to be read.
- ns: A pointer to a long long integer where the current elapsed time in microseconds will be stored.
Examples
Simple usage:
#include <papi.h>
int main() {
int EventSet = PAPI_NULL;
long long ns;
PAPI_create_eventset(&EventSet);
PAPI_add_event(EventSet, PAPI_TOT_CYC);
PAPI_start(EventSet);
// Perform some code whose execution time we want to measure
PAPI_read_stopwatch_us(EventSet, &ns);
printf("Elapsed time: %lld microseconds\n", ns);
PAPI_stop(EventSet);
PAPI_cleanup_eventset(EventSet);
return 0;
}
Common Issues
- Uninitialized EventSet: Ensure that the EventSet has been created and initialized before using this function.
- Invalid Event: Check that the EventSet contains a stopwatch event (e.g., PAPI_TOT_CYC).
- Negative Elapsed Time: If the elapsed time is less than zero, it indicates an error in using the function.
Integration
This function can be integrated with other Linux performance tools, such as perf
, for comprehensive performance profiling and optimization.
Related Commands
PAPI_start()
: Starts the specified EventSet and begins accumulating event values.PAPI_stop()
: Stops the specified EventSet and ceases accumulating event values.PAPI_cleanup_eventset()
: Frees the memory allocated for the specified EventSet.