nmi_watchdog.c

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/* If the NMI watchdog is enabled it will steal a performance counter.   */
/* There is a bug that if you try to use the maximum number of counters  */
/*   (not counting the stolen one) with a group leader, sys_perf_open()  */
/* will indicate success, as will starting the count, but you will fail  */
/* at read time.                                                         */
 
/* This bug still exists in 3.x */
/* The perf NMI watchdog was not introduced until 2.6.34        */
 
/* This also triggers in the case of the schedulability bug      */
/* but since that was fixed in 2.6.34 then in theory there is    */
/* no overlap in the tests.                                      */
 
#include <stdio.h>
 
#include "papi.h"
#include "papi_test.h"
 
 
static int detect_nmi_watchdog(void) {
 
    int watchdog_detected=0,watchdog_value=0;
    FILE *fff;
 
    fff=fopen("/proc/sys/kernel/nmi_watchdog","r");
    if (fff!=NULL) {
        if (fscanf(fff,"%d",&watchdog_value)==1) {
            if (watchdog_value>0) watchdog_detected=1;
        }
        fclose(fff);
    }
    else {
        watchdog_detected=-1;
    }
 
    return watchdog_detected;
}
 
int main( int argc, char **argv ) {
 
    int retval,watchdog_active=0;
    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 );
    }
 
    watchdog_active=detect_nmi_watchdog();
 
    if (watchdog_active<0) {
        test_skip( __FILE__, __LINE__,
            "nmi_watchdog file does not exist\n", 0);
    }
 
    if (watchdog_active) {
        if (!quiet) {
    printf("\nOn perf_event kernels with the nmi_watchdog enabled\n");
    printf("the watchdog steals an event, but the scheduability code\n");
    printf("is not notified.  Thus adding a full complement of events\n");
    printf("seems to pass, but then fails at read time.\n");
    printf("Because of this, PAPI has to do some slow workarounds.\n");
    printf("For best PAPI performance, you may wish to disable\n");
    printf("the watchdog by running (as root)\n");
    printf("\techo \"0\" > /proc/sys/kernel/nmi_watchdog\n\n");
        }
 
        test_warn( __FILE__, __LINE__,
            "NMI Watchdog Active, enabling slow workarounds", 0 );
    }
 
    test_pass( __FILE__ );
 
    return 0;
}