scheduler.cpp

This tutorial show how to use the low-level scheduler to generate efficient custom OpenCL kernels at run time. The purpose of the scheduler is to provide a low-level interface for interfacing ViennaCL from languages other than C++, yet providing the user the ability to specify complex operations. Typical consumers are scripting languages such as Python (e.g. PyViennaCL), but the facility should be used in the future to also fuse compute kernels on the fly.

Warning

The scheduler is experimental and only intended for expert users.

We start this tutorial with including the necessary headers:

// include necessary system headers
#include <iostream>

// include basic scalar and vector types of ViennaCL
#include "viennacl/scalar.hpp"
#include "viennacl/vector.hpp"
#include "viennacl/matrix.hpp"

#include "viennacl/scheduler/execute.hpp"
#include "viennacl/scheduler/io.hpp"

This tutorial sets up three vectors and finally assigns the sum of two to the third. Although this can be achieved with only a few lines of code using the standard ViennaCL C++ API, we go through the low-level interface for demonstration purposes.

int main()
{
  typedef float       ScalarType;  // do not change without adjusting the code for the low-level interface below

Create three vectors, initialize two of them with ascending/descending integers:

viennacl::vector<ScalarType> vcl_vec1(10);
viennacl::vector<ScalarType> vcl_vec2(10);
viennacl::vector<ScalarType> vcl_vec3(10);

for (unsigned int i = 0; i < 10; ++i)
{
  vcl_vec1[i] = ScalarType(i);
  vcl_vec2[i] = ScalarType(10 - i);
}

Build expression graph for the operation vcl_vec3 = vcl_vec1 + vcl_vec2

This requires the following expression graph:

         ( = )
        /      |
vcl_vec3      ( + )
             /     |
       vcl_vec1    vcl_vec2

One expression node consists of two leaves and the operation connecting the two. Here we thus need two nodes: One for {vcl_vec3, = , link}, where 'link' points to the second node {vcl_vec1, +, vcl_vec2}.

The following is the lowest level on which one could build the expression tree. Even for a C API one would introduce some additional convenience layer such as add_vector_float_to_lhs(...); etc.

typedef viennacl::scheduler::statement::container_type   NodeContainerType;   // this is just std::vector<viennacl::scheduler::statement_node>
NodeContainerType expression_nodes(2);                                        //container with two nodes

First Node (Assignment)

// specify LHS of first node, i.e. vcl_vec3:
expression_nodes[0].lhs.type_family  = viennacl::scheduler::VECTOR_TYPE_FAMILY;   // family of vectors
expression_nodes[0].lhs.subtype      = viennacl::scheduler::DENSE_VECTOR_TYPE;    // a dense vector
expression_nodes[0].lhs.numeric_type = viennacl::scheduler::FLOAT_TYPE;           // vector consisting of floats
expression_nodes[0].lhs.vector_float = &vcl_vec3;                                 // provide pointer to vcl_vec3;

// specify assignment operation for this node:
expression_nodes[0].op.type_family   = viennacl::scheduler::OPERATION_BINARY_TYPE_FAMILY; // this is a binary operation, so both LHS and RHS operands are important
expression_nodes[0].op.type          = viennacl::scheduler::OPERATION_BINARY_ASSIGN_TYPE; // assignment operation: '='

// specify RHS: Just refer to the second node:
expression_nodes[0].rhs.type_family  = viennacl::scheduler::COMPOSITE_OPERATION_FAMILY; // this links to another node (no need to set .subtype and .numeric_type)
expression_nodes[0].rhs.node_index   = 1;                                               // index of the other node

Second Node (Addition)

// LHS
expression_nodes[1].lhs.type_family  = viennacl::scheduler::VECTOR_TYPE_FAMILY;   // family of vectors
expression_nodes[1].lhs.subtype      = viennacl::scheduler::DENSE_VECTOR_TYPE;    // a dense vector
expression_nodes[1].lhs.numeric_type = viennacl::scheduler::FLOAT_TYPE;           // vector consisting of floats
expression_nodes[1].lhs.vector_float = &vcl_vec1;                                 // provide pointer to vcl_vec1

// OP
expression_nodes[1].op.type_family   = viennacl::scheduler::OPERATION_BINARY_TYPE_FAMILY; // this is a binary operation, so both LHS and RHS operands are important
expression_nodes[1].op.type          = viennacl::scheduler::OPERATION_BINARY_ADD_TYPE;    // addition operation: '+'

// RHS
expression_nodes[1].rhs.type_family  = viennacl::scheduler::VECTOR_TYPE_FAMILY;  // family of vectors
expression_nodes[1].rhs.subtype      = viennacl::scheduler::DENSE_VECTOR_TYPE;   // a dense vector
expression_nodes[1].rhs.numeric_type = viennacl::scheduler::FLOAT_TYPE;          // vector consisting of floats
expression_nodes[1].rhs.vector_float = &vcl_vec2;                                // provide pointer to vcl_vec2

Create the full statement (aka. single line of code such as vcl_vec3 = vcl_vec1 + vcl_vec2):

viennacl::scheduler::statement vec_addition(expression_nodes);

Print the expression. Resembles the tree outlined in comments above.

std::cout << vec_addition << std::endl;

Execute the operation

viennacl::scheduler::execute(vec_addition);

Print vectors in order to check the result:

std::cout << "vcl_vec1: " << vcl_vec1 << std::endl;
std::cout << "vcl_vec2: " << vcl_vec2 << std::endl;
std::cout << "vcl_vec3: " << vcl_vec3 << std::endl;

That's it! Print success message and exit.

  std::cout << "!!!! TUTORIAL COMPLETED SUCCESSFULLY !!!!" << std::endl;

  return EXIT_SUCCESS;
}

Full Example Code

/* =========================================================================
   Copyright (c) 2010-2015, Institute for Microelectronics,
                            Institute for Analysis and Scientific Computing,
                            TU Wien.
   Portions of this software are copyright by UChicago Argonne, LLC.

                            -----------------
                  ViennaCL - The Vienna Computing Library
                            -----------------

   Project Head:    Karl Rupp                   rupp@iue.tuwien.ac.at

   (A list of authors and contributors can be found in the PDF manual)

   License:         MIT (X11), see file LICENSE in the base directory
============================================================================= */

// include necessary system headers
#include <iostream>

// include basic scalar and vector types of ViennaCL
#include "viennacl/scalar.hpp"
#include "viennacl/vector.hpp"
#include "viennacl/matrix.hpp"

#include "viennacl/scheduler/execute.hpp"
#include "viennacl/scheduler/io.hpp"


int main()
{
  typedef float       ScalarType;  // do not change without adjusting the code for the low-level interface below

  viennacl::vector<ScalarType> vcl_vec1(10);
  viennacl::vector<ScalarType> vcl_vec2(10);
  viennacl::vector<ScalarType> vcl_vec3(10);

  for (unsigned int i = 0; i < 10; ++i)
  {
    vcl_vec1[i] = ScalarType(i);
    vcl_vec2[i] = ScalarType(10 - i);
  }

  typedef viennacl::scheduler::statement::container_type   NodeContainerType;   // this is just std::vector<viennacl::scheduler::statement_node>
  NodeContainerType expression_nodes(2);                                        //container with two nodes

  // specify LHS of first node, i.e. vcl_vec3:
  expression_nodes[0].lhs.type_family  = viennacl::scheduler::VECTOR_TYPE_FAMILY;   // family of vectors
  expression_nodes[0].lhs.subtype      = viennacl::scheduler::DENSE_VECTOR_TYPE;    // a dense vector
  expression_nodes[0].lhs.numeric_type = viennacl::scheduler::FLOAT_TYPE;           // vector consisting of floats
  expression_nodes[0].lhs.vector_float = &vcl_vec3;                                 // provide pointer to vcl_vec3;

  // specify assignment operation for this node:
  expression_nodes[0].op.type_family   = viennacl::scheduler::OPERATION_BINARY_TYPE_FAMILY; // this is a binary operation, so both LHS and RHS operands are important
  expression_nodes[0].op.type          = viennacl::scheduler::OPERATION_BINARY_ASSIGN_TYPE; // assignment operation: '='

  // specify RHS: Just refer to the second node:
  expression_nodes[0].rhs.type_family  = viennacl::scheduler::COMPOSITE_OPERATION_FAMILY; // this links to another node (no need to set .subtype and .numeric_type)
  expression_nodes[0].rhs.node_index   = 1;                                               // index of the other node

  // LHS
  expression_nodes[1].lhs.type_family  = viennacl::scheduler::VECTOR_TYPE_FAMILY;   // family of vectors
  expression_nodes[1].lhs.subtype      = viennacl::scheduler::DENSE_VECTOR_TYPE;    // a dense vector
  expression_nodes[1].lhs.numeric_type = viennacl::scheduler::FLOAT_TYPE;           // vector consisting of floats
  expression_nodes[1].lhs.vector_float = &vcl_vec1;                                 // provide pointer to vcl_vec1

  // OP
  expression_nodes[1].op.type_family   = viennacl::scheduler::OPERATION_BINARY_TYPE_FAMILY; // this is a binary operation, so both LHS and RHS operands are important
  expression_nodes[1].op.type          = viennacl::scheduler::OPERATION_BINARY_ADD_TYPE;    // addition operation: '+'

  // RHS
  expression_nodes[1].rhs.type_family  = viennacl::scheduler::VECTOR_TYPE_FAMILY;  // family of vectors
  expression_nodes[1].rhs.subtype      = viennacl::scheduler::DENSE_VECTOR_TYPE;   // a dense vector
  expression_nodes[1].rhs.numeric_type = viennacl::scheduler::FLOAT_TYPE;          // vector consisting of floats
  expression_nodes[1].rhs.vector_float = &vcl_vec2;                                // provide pointer to vcl_vec2


  viennacl::scheduler::statement vec_addition(expression_nodes);

  std::cout << vec_addition << std::endl;

  viennacl::scheduler::execute(vec_addition);

  std::cout << "vcl_vec1: " << vcl_vec1 << std::endl;
  std::cout << "vcl_vec2: " << vcl_vec2 << std::endl;
  std::cout << "vcl_vec3: " << vcl_vec3 << std::endl;

  std::cout << "!!!! TUTORIAL COMPLETED SUCCESSFULLY !!!!" << std::endl;

  return EXIT_SUCCESS;
}