Pipeline

Reporting

Pipelines

Pipelines are reported in the following format:

Pipeline at: 1:11
Start line: 1:30
End line: 1:34
Stages:
    <stage_1>

    <stage_2>

    ...

The reported values shall be interpreted as follows:

• Pipeline at: <file_id>:<cu_id>, where the respective parent file can be looked up in the FileMapping.txt using file_id and cu_id can be used for a look up in Data.xml
• Start line: <file_id>:<line_num>, where line_num refers to the first source code line of the identified pipeline.
• End line: <file_id>:<line_num>, where line_num refers to the last line of the pipeline loop.
• Stages defines a list of stages contained in the identified pipeline. The specific format of the stages is described in the following.

Pipeline Stages

Individual stages of a pipeline are reported in the following format:

Node: 1:13
Start line: 1:31
End line: 1:31
pragma: "#pragma omp task"
first private: ['i']
private: []
shared: ['d', 'in']
reduction: []
InDeps: []
OutDeps: ['a']
InOutDeps: []

The reported values shall be interpreted as follows:

• Node: <file_id>:<cu_id>, where the respective parent file can be looked up in the FileMapping.txt using file_id and cu_id can be used for a look up in Data.xml
• Start line: <file_id>:<line_num>, where line_num refers to the first source code line of the identified pipeline stage.
• End line: <file_id>:<line_num>, where line_num refers to the last line of the stage.
• pragma:shows which type of OpenMP pragma shall be inserted before the start line.
• private: [<vars>] lists a set of variables which have been identified as thread-private
• The same interpretation applies to the following values aswell:
  • shared
  • first_private
• reduction: [<operation>:<var>] specifies a set of identified reduction operations and variables.
• InDeps: [<vars>] specifies in-dependencies according to the OpenMP depend clause.
• OutDeps: [<vars>] specifies out-dependencies according to the OpenMP depend clause.
• InOutDeps: [<vars>] specifies inout-dependencies according to the OpenMP depend clause.

Implementation

In order to implement a suggested pipeline, first navigate to the source code location specified by Pipeline at:. For each individual stage the following OpenMP pragmas and closes need to be added to the source code, if the respective lists are not empty:

• Insert pragma prior to the start line mentioned by the stage.
• If private is not empty, add the clause private(<vars>), where vars are separated by commas to the pragma.
• Do the same for:
  • shared -> clause: shared(<vars>)
  • first_private -> clause: firstprivate(<vars>)
  • reduction-> clause: reduction(<operation>:<vars>)
  • InDeps -> clause: depend(in:<vars>)
  • OutDeps -> clause: depend(out:<vars>)
  • InOutDeps -> clause: depend(inout:<vars>)

Example

As an example, we will analyze the following code snippet for parallelization potential. Some location and meta data will be ignored for the sake of simplicity.

int i;
int d=20,a=22, b=44,c=90;
for (i=0; i<100; i++) {
    a = foo(i, d);
    b = bar(a, d);
    c = delta(b, d);
}
a = b;

Analyzing this code snippet results in the following parallelization suggestion:

Pipeline at:
Start line: 1:3
End line: 1:7
Stages:
Node: 1:13
	Start line: 1:4
	End line: 1:4

	shared: ['d', 'in']
	reduction: []
	InDeps: []
	OutDeps: ['a']
	InOutDeps: []

	Start line: 1:5
	End line: 1:5
	pragma: "#pragma omp task"
	first private: []
	private: []
	shared: ['d', 'in']
	reduction: []
	InDeps: ['a']
	OutDeps: ['b']
	InOutDeps: []

	Start line: 1:6
	End line: 1:7
	pragma: "#pragma omp task"
	first private: []
	private: ['c']
	shared: ['d', 'in']
	reduction: []
	InDeps: ['b']
	OutDeps: []
	InOutDeps: []

After interpreting and implementing the suggestion, the resulting, now parallel, source code could look as follows:

int i;
int d=20,a=22, b=44,c=90;
for (i=0; i<100; i++) {
    #pragma omp task firsprivate(i) shared(d, in) depend(out:a)
    a = foo(i, d);
    #pragma omp task shared(d, in) depend(in:a) depend(out:b)
    b = bar(a, d);
    #pragma omp task private(c) shared(d, in) depend(in: b)
    c = delta(b, d);
}
a = b;