cetus.codegen

Class ProfitableOMP

java.lang.Object

cetus.codegen.CodeGenPass

cetus.codegen.ProfitableOMP

public class ProfitableOMP
extends CodeGenPass

This pass performs postprocessing of programs parallelized with OpenMP. Two methods, one with simple performance model and the other with guiding profiler, are provided. Both methods make use of "if" clause provided by the OpenMP specification.

Model-based approach (starts with -profitable-omp=1)
Symbolically computes the workload of each loop by counting loop iteration and the child statements. If the workload is smaller than the given threshold, it is serialized either at compile-time (if the workload is integer literal) or at run-time (through OpenMP if clause). Following sub options are allowed through command line:

     threshold=N  the threshold for serialization
     costwhile=N  the iteration count for while-like loops
     costfcall=N  the workload of a function call
     runtime=0|1  when this value is zero OpenMP if clause is avoided
   e.g., -profitable-omp=1:threshold=10000,costwhile=100,costfcall=100
 

Profile-based approach (starts with -profitable-omp=2)
This approach assumes the workload of a parallel loop does not change over multiple invocations of the loop. The basic idea is to use profiled runtime of a sequential execution and a parallel execution of a parallel loop and to decide whether the loop should be executed in parallel after the profiling. A parallel loop is executed in three different phases:

     grace phase  : the loop is executed in parallel
     profile phase: the loop is profiled several times both in serial and
                    in parallel
     stable phase : the loop is executed either in serial or in parallel
                    based on the profiled information
 

Users can vary the behavior of each phase by specifying the following sub options:

     grace=N   : the length of grace phase (# invocations)
     repeat=N  : the number of profiled invocations in serial/parallel
     interval=N: the interval between successive profiling within the
                 profile phase
     usmin=N   : threshold for eager serialization without profiling in
                 micro seconds 
   e.g., -profitable-omp=2:grace=50,repeat=5,interval=10,usmin=10
 

Constructor Summary

Constructors

Constructor and Description
ProfitableOMP(Program program) Constructs a new profitable code generator for OpenMP programs.

Method Summary

Methods

Modifier and Type	Method and Description
java.lang.String	getPassName() Returns the name of this code generation pass.
void	start() Starts the code generation for profitable loop parallelization.

Methods inherited from class cetus.codegen.CodeGenPass

run

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ProfitableOMP

public ProfitableOMP(Program program)

Constructs a new profitable code generator for OpenMP programs.

Parameters:

program - the program to be processed.

Method Detail

getPassName

public java.lang.String getPassName()

Returns the name of this code generation pass.

Specified by:

getPassName in class CodeGenPass

start

public void start()

Starts the code generation for profitable loop parallelization.

Specified by:

start in class CodeGenPass