How to use PAPI periodically for performance measurements

Question

I want to analyze system's performance for my application using PAPI api in C. The general structure is that
-- Initialize PAPI
-- Initialize counters of interest
-- start counters
-- run main logic of the application
-- end counters and read values

I want to read the counters periodically say every 1 second instead of reading the final values at the end of the application. does the PAPI output give the aggregate values at end of program execution like the total number of L2 cache misses after the program execution. Another example would be to read number of instructions at every time instance rather than total number of instructions at the end of the program.

Answer 1

Did you get any ideas regarding this? I am doing the same thing, but I am getting strange results: my counters are not updated as often as I'd like them.

For the record, here is a sample that I tested and works well:

#include <papi.h>
#include <stdio.h>
#include <stdlib.h>

main()
{
int retval, EventSet = PAPI_NULL;
long_long values[3];
    unsigned counter;
    unsigned c;
    unsigned long fact;
    unsigned stoppoint;


        /* Initialize the PAPI library */
        retval = PAPI_library_init(PAPI_VER_CURRENT);

        if (retval != PAPI_VER_CURRENT) {
          fprintf(stderr, "PAPI library init error!\n");
          exit(1);
        }

        /* Create the Event Set */
        if (PAPI_create_eventset(&EventSet) != PAPI_OK)
            printf ("%s:%d\t ERROR\n", __FILE__, __LINE__);

        /* Add Total Instructions Executed to our EventSet */
        if (PAPI_add_event(EventSet, PAPI_TOT_INS) != PAPI_OK)
            printf ("%s:%d\t ERROR\n", __FILE__, __LINE__);

        /* Add Total Instructions Executed to our EventSet */
        if (PAPI_add_event(EventSet, PAPI_TOT_CYC) != PAPI_OK)
            printf ("%s:%d\t ERROR\n", __FILE__, __LINE__);

        /* Add Total Instructions Executed to our EventSet */
        if (PAPI_add_event(EventSet, PAPI_LST_INS) != PAPI_OK)
            printf ("%s:%d\t ERROR\n", __FILE__, __LINE__);


   srand ( time(NULL) );
   stoppoint = 50+(rand() % 100);
/* Do some computation here */
    for (counter = 0; counter < stoppoint; counter++)
    {
        /* Initialize the PAPI library */
        retval = PAPI_library_init(PAPI_VER_CURRENT);

        if (retval != PAPI_VER_CURRENT) {
          fprintf(stderr, "PAPI library init error!\n");
          exit(1);
        }


        /* Start counting */
        if (PAPI_start(EventSet) != PAPI_OK)
            printf ("%s:%d\t ERROR\n", __FILE__, __LINE__);


                fact = 1;
        for (c = 1; c <= counter; c++)
        {
                     fact = c * c;
        }




        printf("Factorial of %d is %lu\n", counter, fact);
        if (PAPI_read(EventSet, values) != PAPI_OK)
            printf ("%s:%d\t ERROR\n", __FILE__, __LINE__);
        printf ("\nTotal Instructions Completed:\t%lld\t Total Cycles:\t%lld\tLoad Store Instructions\t%lld\n\n", values[0], values[1], values[2]);
        /* Do some computation here */

        if (PAPI_stop(EventSet, values) != PAPI_OK)
            printf ("%s:%d\t ERROR\n", __FILE__, __LINE__);

            }
        /* End of computation */


}