Table of Contents

PAPI

<html> <h3> <span style=“color:red;font-size:100%;”>P</span>erformance <span style=“color:red;font-size:100%;”>A</span>pplication <span style=“color:red;font-size:100%;”>P</span>rogramming <span style=“color:red;font-size:100%;”>I</span>nterface </h2> </html>

Synopsis

PAPI (Performance Application Programming Interface) has been developed at the University of Tennessee’s Innovative Computing Laboratory in the Computer Science Department. PAPI is an event-based profiling library providing access to hardware performance counters of critical events, e.g., cache misses, number of CYCLES, number of floating point instructions (flpins), or floating point operations per second (FLOPs). These events can be monitored for selected sections of the code allowing for the analysis of the efficiency of mapping the code to the underlying hardware architecture.

Types of events

Native events are countable by the CPU and can such be accessed directly or by the PAPI low-level interface delivering a CPU-specific bit pattern.

Preset or predefined events are software abstractions of architecture-dependent native events that are accessible through the PAPI interface. papiStdEventDefs.h includes a collection of about 100 preset events, e.g., memory hierarchy, cache coherence protocol events, cycle and instruction counts, functional unit, and pipeline status. However, due to hardware implementation differences, it is sometimes only possible to count similar (not the same) types of events on different platforms implying that the direct comparison of particular PAPI event counts is not necessarily suitable.

Usage of PAPI

The user will have to modify the source code and insert PAPI calls (see below: Interfacing with PAPI). Invocation and usage simply requires to load the PAPI module,

 module purge
 module load papi/5.4.3

and, to compile the user's code while linking the PAPI library (-lpapi), i.e., for C users,

 gcc my_program.c -lpapi    
 ./a.out   

or for Fortran users,

 gfortran  my_program.f -I/opt/sw/x86_64/glibc-2.12/ivybridge-ep/papi/5.4.3/gnu-4.4.7/include -lpapi
 ./a.out

Interfacing with PAPI : Low level interface

In general, some code section to be analyzed with PAPI needs to be wrapped into a sequence of standard PAPI calls. Here, code examples for

As stated in the comment of the C code above, it is best to analyze one particular event at a time. This advice is given because the CPU has limitations in combining arbitrary counters at a time.

Interfacing with PAPI : High level interface

The high-level API combines the counters for a specified list of PAPI preset events, only. The set of implemented high level functions is quite limited and can be found in the section The High Level API next to the last paragraph of papi.h. It can also be used in conjunction with the low-level API. An example of the usage of the high level API can be found here for C users.

Practical tips: