commit 4718b4816fbb891c0adfca6412c99257c216e925

Author: William Cohen <wcohen@redhat.com>

Date:   Thu May 19 14:28:42 2016 -0400

    Force all processors to check event schedulability by reading the counters

    There are situations where the perf_event_open syscall will return a

    file descriptor for a set of events even when they cannot be scheduled

    together.  This occurs on 32-bit and 64-bit ARM processors and MIPS

    processors.  This problem also occurs on linux kernels older than

    2.6.33 and when the watchdog timer steals a performance counter.  To

    check that the performance counters are properly setup PAPI needs to

    check that the counter values can be successfully read.  Rather than

    trying to avoid this test PAPI will now always do it.

    Signed-off-by: William Cohen <wcohen@redhat.com>

diff --git a/src/components/perf_event/perf_event.c b/src/components/perf_event/perf_event.c

index d9c2c77..5698173 100644

--- a/src/components/perf_event/perf_event.c

+++ b/src/components/perf_event/perf_event.c

@@ -58,9 +58,6 @@

 #define PERF_EVENTS_OPENED  0x01

 #define PERF_EVENTS_RUNNING 0x02

-/* Static globals */

-int nmi_watchdog_active;

-

 /* Forward declaration */

 papi_vector_t _perf_event_vector;

@@ -180,34 +177,6 @@ pe_vendor_fixups(papi_vector_t *vector)

 /******** Kernel Version Dependent Routines  **********************/

 /******************************************************************/

-/* KERNEL_CHECKS_SCHEDUABILITY_UPON_OPEN is a work-around for kernel arch

- * implementations (e.g. x86) which don't do a static event scheduability

- * check in sys_perf_event_open.

- * This was fixed for x86 in the 2.6.33 kernel

- *

- * Also! Kernels newer than 2.6.34 will fail in a similar way

- *       if the nmi_watchdog has stolen a performance counter

- *       and we try to use the maximum number of counters.

- *       A sys_perf_event_open() will seem to succeed but will fail

- *       at read time.  So re-use this work around code.

- */

-static int

-bug_check_scheduability(void) {

-

-#if defined(__powerpc__)

-  /* PowerPC not affected by this bug */

-#elif defined(__mips__)

-  /* MIPS as of kernel 3.1 does not properly detect schedulability */

-  return 1;

-#else

-  if (_papi_os_info.os_version < LINUX_VERSION(2,6,33)) return 1;

-#endif

-

-  if (nmi_watchdog_active) return 1;

-

-  return 0;

-}

-

 /* PERF_FORMAT_GROUP allows reading an entire group's counts at once   */

 /* before 2.6.34 PERF_FORMAT_GROUP did not work when reading results   */

 /*  from attached processes.  We are lazy and disable it for all cases */

@@ -508,68 +477,65 @@ check_scheduability( pe_context_t *ctx, pe_control_t *ctl, int idx )

    long long papi_pe_buffer[READ_BUFFER_SIZE];

    int i,group_leader_fd;

-   if (bug_check_scheduability()) {

+   /* If the kernel isn't tracking scheduability right       */

+   /* Then we need to start/stop/read to force the event     */

+   /* to be scheduled and see if an error condition happens. */

+

+   /* get the proper fd to start */

+   group_leader_fd=ctl->events[idx].group_leader_fd;

+   if (group_leader_fd==-1) group_leader_fd=ctl->events[idx].event_fd;

+

+   /* start the event */

+   retval = ioctl( group_leader_fd, PERF_EVENT_IOC_ENABLE, NULL );

+   if (retval == -1) {

+      PAPIERROR("ioctl(PERF_EVENT_IOC_ENABLE) failed");

+      return PAPI_ESYS;

+   }

-      /* If the kernel isn't tracking scheduability right       */

-      /* Then we need to start/stop/read to force the event     */

-      /* to be scheduled and see if an error condition happens. */

+   /* stop the event */

+   retval = ioctl(group_leader_fd, PERF_EVENT_IOC_DISABLE, NULL );

+   if (retval == -1) {

+      PAPIERROR( "ioctl(PERF_EVENT_IOC_DISABLE) failed" );

+      return PAPI_ESYS;

+   }

-      /* get the proper fd to start */

-      group_leader_fd=ctl->events[idx].group_leader_fd;

-      if (group_leader_fd==-1) group_leader_fd=ctl->events[idx].event_fd;

+   /* See if a read returns any results */

+   cnt = read( group_leader_fd, papi_pe_buffer, sizeof(papi_pe_buffer));

+   if ( cnt == -1 ) {

+      SUBDBG( "read returned an error!  Should never happen.\n" );

+      return PAPI_ESYS;

+   }

-      /* start the event */

-      retval = ioctl( group_leader_fd, PERF_EVENT_IOC_ENABLE, NULL );

-      if (retval == -1) {

-	 PAPIERROR("ioctl(PERF_EVENT_IOC_ENABLE) failed");

-	 return PAPI_ESYS;

-      }

+   if ( cnt == 0 ) {

+      /* We read 0 bytes if we could not schedule the event */

+      /* The kernel should have detected this at open       */

+      /* but various bugs (including NMI watchdog)          */

+      /* result in this behavior                            */

-      /* stop the event */

-      retval = ioctl(group_leader_fd, PERF_EVENT_IOC_DISABLE, NULL );

-      if (retval == -1) {

-	 PAPIERROR( "ioctl(PERF_EVENT_IOC_DISABLE) failed" );

-	 return PAPI_ESYS;

-      }

+      return PAPI_ECNFLCT;

-      /* See if a read returns any results */

-      cnt = read( group_leader_fd, papi_pe_buffer, sizeof(papi_pe_buffer));

-      if ( cnt == -1 ) {

-	 SUBDBG( "read returned an error!  Should never happen.\n" );

-	 return PAPI_ESYS;

-      }

+   } else {

-      if ( cnt == 0 ) {

-         /* We read 0 bytes if we could not schedule the event */

-         /* The kernel should have detected this at open       */

-         /* but various bugs (including NMI watchdog)          */

-         /* result in this behavior                            */

-

-	 return PAPI_ECNFLCT;

-

-     } else {

-

-	/* Reset all of the counters (opened so far) back to zero      */

-	/* from the above brief enable/disable call pair.              */

-

-	/* We have to reset all events because reset of group leader      */

-        /* does not reset all.                                            */

-	/* we assume that the events are being added one by one and that  */

-        /* we do not need to reset higher events (doing so may reset ones */

-        /* that have not been initialized yet.                            */

-

-	/* Note... PERF_EVENT_IOC_RESET does not reset time running       */

-	/* info if multiplexing, so we should avoid coming here if        */

-	/* we are multiplexing the event.                                 */

-        for( i = 0; i < idx; i++) {

-	   retval=ioctl( ctl->events[i].event_fd, PERF_EVENT_IOC_RESET, NULL );

-	   if (retval == -1) {

-	      PAPIERROR( "ioctl(PERF_EVENT_IOC_RESET) #%d/%d %d "

-			 "(fd %d)failed",

-			 i,ctl->num_events,idx,ctl->events[i].event_fd);

-	      return PAPI_ESYS;

-	   }

-	}

+      /* Reset all of the counters (opened so far) back to zero      */

+      /* from the above brief enable/disable call pair.              */

+

+      /* We have to reset all events because reset of group leader      */

+      /* does not reset all.                                            */

+      /* we assume that the events are being added one by one and that  */

+      /* we do not need to reset higher events (doing so may reset ones */

+      /* that have not been initialized yet.                            */

+

+      /* Note... PERF_EVENT_IOC_RESET does not reset time running       */

+      /* info if multiplexing, so we should avoid coming here if        */

+      /* we are multiplexing the event.                                 */

+      for( i = 0; i < idx; i++) {

+	 retval=ioctl( ctl->events[i].event_fd, PERF_EVENT_IOC_RESET, NULL );

+	 if (retval == -1) {

+	    PAPIERROR( "ioctl(PERF_EVENT_IOC_RESET) #%d/%d %d "

+		       "(fd %d)failed",

+		       i,ctl->num_events,idx,ctl->events[i].event_fd);

+	    return PAPI_ESYS;

+	 }

       }

    }

    return PAPI_OK;

@@ -1658,8 +1624,7 @@ _pe_init_component( int cidx )

   }

   /* Detect NMI watchdog which can steal counters */

-  nmi_watchdog_active=_linux_detect_nmi_watchdog();

-  if (nmi_watchdog_active) {

+  if (_linux_detect_nmi_watchdog()) {

     SUBDBG("The Linux nmi_watchdog is using one of the performance "

 	   "counters, reducing the total number available.\n");

   }