papi_ref_cyc.c

Go to the documentation of this file.

/* This test exercises the PAPI_TOT_CYC and PAPI_REF_CYC counters.

    PAPI_TOT_CYC should measure the number of cycles required to do
    a fixed amount of work.
    It should be roughly constant for constant work, regardless of the
    speed state a core is in.

    PAPI_REF_CYC should measure the number of cycles at a constant
    reference clock rate, independent of the actual clock rate of the core.
*/

/*
    PAPI_REF_CYC has various issues on Intel chips:

    On older machines PAPI uses UNHALTED_REFERENCE_CYCLES but this
    means different things on different architectures

    + On Core2/Atom this maps to the special Fixed Counter 2
        CPU_CLK_UNHALTED.REF
        This counts at the same rate as the TSC (PAPI_get_real_cyc())
        And also seems to match PAPI_TOT_CYC
        It is documented as having a fixed ratio to the
        CPU_CLK_UNHALTED.BUS (3c/1) event.

    + On Nehalem/Westemere this also maps to Fixed Counter 2.
        Again, counts same rate as the TSC  and returns
        CPU_CLK_UNHALTED.REF_P (3c/1)
        times the "Maximum Non-Turbo Ratio"

    + Same for Sandybridge/Ivybridge

    On newer HSW,BDW,SKL machines PAPI uses a different type of event
    CPU_CLK_THREAD_UNHALTED:REF_XCLK

    + On Haswell machines this is just the reference clock
        (100MHz?)
    + On Sandybridge this is off by a factor of 8x?
*/

/* NOTE:
    PAPI_get_virt_cyc() returns a lie!
    It's just virt_time() * max_theoretical_MHz
    so no point in checking that */

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

#include "papi.h"
#include "papi_test.h"

#include "testcode.h"

#define NUM_FLOPS  20000000

static void work (int EventSet, int sleep_test, int quiet)
{
    int retval;
    long long values[2];
    long long elapsed_us, elapsed_cyc, elapsed_virt_us, elapsed_virt_cyc;
    double cycles_error;
    int numflops = NUM_FLOPS;

    /* Gather before stats */
    elapsed_us = PAPI_get_real_usec(  );
    elapsed_cyc = PAPI_get_real_cyc(  );
    elapsed_virt_us = PAPI_get_virt_usec(  );
    elapsed_virt_cyc = PAPI_get_virt_cyc(  );

    /* Start PAPI */
    retval = PAPI_start( EventSet );
    if ( retval != PAPI_OK ) {
        test_fail( __FILE__, __LINE__, "PAPI_start", retval );
    }

    /* our test code */
    if (sleep_test) {
        sleep(2);
    }
    else {
        do_flops( numflops, 1 );
    }

    /* Stop PAPI */
    retval = PAPI_stop( EventSet, values );
    if ( retval != PAPI_OK ) {
       test_fail( __FILE__, __LINE__, "PAPI_stop", retval );
    }

    /* Calculate total values */
    elapsed_virt_us = PAPI_get_virt_usec(  ) - elapsed_virt_us;
    elapsed_virt_cyc = PAPI_get_virt_cyc(  ) - elapsed_virt_cyc;
    elapsed_us = PAPI_get_real_usec(  ) - elapsed_us;
    elapsed_cyc = PAPI_get_real_cyc(  ) - elapsed_cyc;

    if (!quiet) {
        printf( "-------------------------------------------------------------------------\n" );
        if (sleep_test) printf("Sleeping for 2s\n");
        else printf( "Using %d iterations of c += a*b\n", numflops );
        printf( "-------------------------------------------------------------------------\n" );

        printf( "PAPI_TOT_CYC             : \t%10lld\n", values[0] );
        printf( "PAPI_REF_CYC             : \t%10lld\n", values[1] );
        printf( "Real usec                : \t%10lld\n", elapsed_us );
        printf( "Real cycles              : \t%10lld\n", elapsed_cyc );
        printf( "Virt usec                : \t%10lld\n", elapsed_virt_us );
        printf( "Virt cycles (estimate)   : \t%10lld\n", elapsed_virt_cyc );
        printf( "Estimated GHz            : \t%10.3lf\n", (double) elapsed_cyc/(double)elapsed_us/1000.0);

        printf( "-------------------------------------------------------------------------\n" );
    }


    if (sleep_test) {
        if (!quiet) {
        printf( "Verification: PAPI_REF_CYC should be much lower than real_usec\n");
        }
        if (values[1]>elapsed_us) {
            if (!quiet) printf("PAPI_REF_CYC too high!\n");
            test_fail( __FILE__, __LINE__, "PAPI_REF_CYC too high", 0 );
        }

    }
    else {
        /* PAPI_REF_CYC should be roughly the same as TSC when busy */
        /* on Intel chips */
        if (!quiet) {
        printf( "Verification: real_cyc should be roughly PAPI_REF_CYC\n");
        printf( "              real_usec should be roughly virt_usec (on otherwise idle system)\n");
        }

        cycles_error=100.0*
            ((double)values[1]-((double)elapsed_cyc))
                /values[1];

        if ((cycles_error>10.0) || (cycles_error<-10.0)) {
            if (!quiet) printf("Error of %.2f%%\n",cycles_error);
            test_fail( __FILE__, __LINE__, "PAPI_REF_CYC validation", 0 );
        }

        cycles_error=100.0*
            ((double)elapsed_us-(double)elapsed_virt_us)
                /(double)elapsed_us;

        if ((cycles_error>10.0) || (cycles_error<-10.0)) {
            if (!quiet) printf("Error of %.2f%%\n",cycles_error);
            test_warn( __FILE__, __LINE__, "real_us validation", 0 );
        }
    }
}


int
main( int argc, char **argv )
{
    int retval;
    int EventSet = PAPI_NULL;
    int quiet;

    /* Set TESTS_QUIET variable */
    quiet = tests_quiet( argc, argv );

    /* Init the PAPI library */
    retval = PAPI_library_init( PAPI_VER_CURRENT );
    if ( retval != PAPI_VER_CURRENT ) {
       test_fail( __FILE__, __LINE__, "PAPI_library_init", retval );
    }

    /* Check the ref cycles event */
    retval = PAPI_query_named_event("PAPI_REF_CYC");
    if (PAPI_OK!=retval) {
        if (!quiet) printf("No PAPI_REF_CYC available\n");
        test_skip( __FILE__, __LINE__,
            "PAPI_REF_CYC is not defined on this platform.", 0);
    }

    /* create an eventset */
    retval = PAPI_create_eventset( &EventSet );
    if ( retval != PAPI_OK ) {
        test_fail( __FILE__, __LINE__, "PAPI_create_eventset", retval );
    }

    /* add core cycle event */
    retval = PAPI_add_named_event( EventSet, "PAPI_TOT_CYC");
    if ( retval != PAPI_OK ) {
        test_fail( __FILE__, __LINE__,
                "PAPI_add_named_event: PAPI_TOT_CYC", retval );
    }

    /* add ref cycle event */
    retval = PAPI_add_named_event( EventSet, "PAPI_REF_CYC");
    if ( retval != PAPI_OK ) {
        test_fail( __FILE__, __LINE__,
                "PAPI_add_events: PAPI_REF_CYC", retval );
    }

    if (!quiet) {
        printf("Test case sleeping: "
            "Look at TOT and REF cycles.\n");
    }

    work(EventSet, 1, quiet);
//  do_flops(10*numflops);

    if (!quiet) {
        printf( "\nTest case busy:\n" );
    }

    work(EventSet, 0, quiet);

    test_pass( __FILE__ );

    return 0;
}