The ginkgo-overhead program

The ginkgo overhead measurement example..

Table of contents
Introduction About the example The commented program	Results Comments about programming and debugging The plain program

Introduction

About the example

The commented program

    if (argc == 2) {
        num_iters = std::atol(argv[1]);
        if (num_iters == 0) {
            print_usage_and_exit(argv[0]);
        }
    }
 
    std::cout << gko::version_info::get() << std::endl;
 
    auto exec = gko::ReferenceExecutor::create();
 
    auto cg_factory =
        cg::build()
            .with_criteria(
                gko::stop::Iteration::build().with_max_iters(num_iters))
            .on(exec);
    auto A = gko::initialize<mtx>({1.0}, exec);
    auto b = gko::initialize<vec>({std::nan("")}, exec);
    auto x = gko::initialize<vec>({0.0}, exec);
 
    auto tic = std::chrono::steady_clock::now();
 
    auto solver = cg_factory->generate(gko::give(A));
    solver->apply(x, b);
    exec->synchronize();
 
    auto tac = std::chrono::steady_clock::now();
 
    auto time = std::chrono::duration_cast<std::chrono::nanoseconds>(tac - tic);
    std::cout << "Running " << num_iters
              << " iterations of the CG solver took a total of "
              << static_cast<double>(time.count()) /
                     static_cast<double>(std::nano::den)
              << " seconds." << std::endl
              << "\tAverage library overhead:     "
              << static_cast<double>(time.count()) /
                     static_cast<double>(num_iters)
              << " [nanoseconds / iteration]" << std::endl;
}

Results

This is the expected output:

Running 1000000 iterations of the CG solver took a total of 1.60337 seconds.
    Average library overhead:     1603.37 [nanoseconds / iteration]

Comments about programming and debugging

The plain program

 
#include <ginkgo/ginkgo.hpp>
 
 
#include <chrono>
#include <cmath>
#include <iostream>
 
 
[[noreturn]] void print_usage_and_exit(const char* name)
{
    std::cerr << "Usage: " << name << " [NUM_ITERS]" << std::endl;
    std::exit(-1);
}
 
 
int main(int argc, char* argv[])
{
    using ValueType = double;
    using IndexType = int;
 
    using vec = gko::matrix::Dense<ValueType>;
    using mtx = gko::matrix::Csr<ValueType, IndexType>;
    using cg = gko::solver::Cg<ValueType>;
 
    long unsigned num_iters = 1000000;
    if (argc > 2) {
        print_usage_and_exit(argv[0]);
    }
    if (argc == 2) {
        num_iters = std::atol(argv[1]);
        if (num_iters == 0) {
            print_usage_and_exit(argv[0]);
        }
    }
 
    std::cout << gko::version_info::get() << std::endl;
 
    auto exec = gko::ReferenceExecutor::create();
 
    auto cg_factory =
        cg::build()
            .with_criteria(
                gko::stop::Iteration::build().with_max_iters(num_iters))
            .on(exec);
    auto A = gko::initialize<mtx>({1.0}, exec);
    auto b = gko::initialize<vec>({std::nan("")}, exec);
    auto x = gko::initialize<vec>({0.0}, exec);
 
    auto tic = std::chrono::steady_clock::now();
 
    auto solver = cg_factory->generate(gko::give(A));
    solver->apply(x, b);
    exec->synchronize();
 
    auto tac = std::chrono::steady_clock::now();
 
    auto time = std::chrono::duration_cast<std::chrono::nanoseconds>(tac - tic);
    std::cout << "Running " << num_iters
              << " iterations of the CG solver took a total of "
              << static_cast<double>(time.count()) /
                     static_cast<double>(std::nano::den)
              << " seconds." << std::endl
              << "\tAverage library overhead:     "
              << static_cast<double>(time.count()) /
                     static_cast<double>(num_iters)
              << " [nanoseconds / iteration]" << std::endl;
}