NAME

       PAPI_overflow - Set up an event set to begin registering overflows.

SYNOPSIS

Detailed Description

       PAPI_overflow() marks a specific EventCode in an EventSet to generate an overflow signal
       after every threshold events are counted. More than one event in an event set can be used
       to trigger overflows. In such cases, the user must call this function once for each
       overflowing event. To turn off overflow on a specified event, call this function with a
       threshold value of 0.

       Overflows can be implemented in either software or hardware, but the scope is the entire
       event set. PAPI defaults to hardware overflow if it is available. In the case of software
       overflow, a periodic timer interrupt causes PAPI to compare the event counts against the
       threshold values and call the overflow handler if one or more events have exceeded their
       threshold. In the case of hardware overflow, the counters are typically set to the
       negative of the threshold value and count up to 0. This zero-crossing triggers a hardware
       interrupt that calls the overflow handler. Because of this counter interrupt, the counter
       values for overflowing counters may be very small or even negative numbers, and cannot be
       relied upon as accurate. In such cases the overflow handler can approximate the counts by
       supplying the threshold value whenever an overflow occurs.

       _papi_overflow_handler() is a placeholder for a user-defined function to process overflow
       events. A pointer to this function is passed to the PAPI_overflow routine, where it is
       invoked whenever a software or hardware overflow occurs. This handler receives the
       EventSet of the overflowing event, the Program Counter address when the interrupt
       occurred, an overflow_vector that can be processed to determined which event(s) caused the
       overflow, and a pointer to the machine context, which can be used in a platform-specific
       manor to extract register information about what was happening when the overflow occurred.

       C Interface:
           #include <papi.h>
           int PAPI_overflow (int EventSet, int EventCode, int threshold, int flags,
           PAPI_overflow_handler_t handler );

           (*PAPI_overflow_handler_t) _papi_overflow_handler (int EventSet, void *address,
           long_long overflow_vector, void *context );

       Fortran Interface:
           Not implemented

       Parameters
           EventSet -- an integer handle to a PAPI event set as created by PAPI_create_eventset
           EventCode -- the preset or native event code to be set for overflow detection. This
           event must have already been added to the EventSet.
           threshold -- the overflow threshold value for this EventCode.
           flags -- bitmap that controls the overflow mode of operation. Set to
           PAPI_OVERFLOW_FORCE_SW to force software overflowing, even if hardware overflow
           support is available. If hardware overflow support is available on a given system, it
           will be the default mode of operation. There are situations where it is advantageous
           to use software overflow instead. Although software overflow is inherently less
           accurate, with more latency and processing overhead, it does allow for overflowing on
           derived events, and for the accurate recording of overflowing event counts. These two
           features are typically not available with hardware overflow. Only one type of overflow
           is allowed per event set, so setting one event to hardware overflow and another to
           forced software overflow will result in an error being returned.
           handler -- pointer to the user supplied handler function to call upon overflow
           address -- the Program Counter address at the time of the overflow
           overflow_vector
            -- a long long word containing flag bits to indicate which hardware counter(s) caused
           the overflow
           *context -- pointer to a machine specific structure that defines the register context
           at the time of overflow. This parameter is often unused and can be ignored in the user
           function.

       Return values
           PAPI_OK On success, PAPI_overflow returns PAPI_OK.

           PAPI_EINVAL One or more of the arguments is invalid.
            Most likely a bad threshold value.
           PAPI_ENOMEM Insufficient memory to complete the operation.
           PAPI_ENOEVST The EventSet specified does not exist.
           PAPI_EISRUN The EventSet is currently counting events.
           PAPI_ECNFLCT The underlying counter hardware cannot count this event and other events
           in the EventSet simultaneously. Also can happen if you are trying to overflow both by
           hardware and by forced software at the same time.
           PAPI_ENOEVNT The PAPI event is not available on the underlying hardware.

       Example

           // Define a simple overflow handler:
           void handler(int EventSet, void *address, long_long overflow_vector, void *context)
           {
              fprintf(stderr,\"Overflow at %p! bit=%#llx \\n\",
                       address,overflow_vector);
           }

           // Call PAPI_overflow for an EventSet containing PAPI_TOT_INS,
           // setting the threshold to 100000. Use the handler defined above.
           retval = PAPI_overflow(EventSet, PAPI_TOT_INS, 100000, 0, handler);

       See also
           PAPI_get_overflow_event_index

Author

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