BenchFalseSharing

BenchFalseSharing.cpp

#include <atomic>
#include <ctime>
#include <iostream>
#include <thread>

static constexpr int workerCount = 1;
static constexpr uint64_t target = 400'000'000;
// Vary this value between 0 and 128 to see the difference.
static constexpr int paddingSize = 128;

struct object {
    std::atomic_uint64_t input = 0;
    char padding[paddingSize];
    std::atomic_uint64_t output = 0;
};

static void inputF(object &obj, uint64_t target)
{
    while (obj.input.fetch_add(1, std::memory_order_relaxed) < target)
        continue;
}

static void outputF(object &obj, uint64_t target)
{
    while (obj.output.fetch_add(1, std::memory_order_relaxed) < target)
        continue;
}

int main()
{
    object obj;
    std::thread inputWorkers[workerCount];
    std::thread outputWorkers[workerCount];

    timespec t1;
    clock_gettime(CLOCK_MONOTONIC, &t1);
    for (std::thread &t : inputWorkers)
        t = std::thread(inputF, std::ref(obj), target);
    for (std::thread &t : outputWorkers)
        t = std::thread(outputF, std::ref(obj), target);
    for (std::thread &t : inputWorkers)
        t.join();
    for (std::thread &t : outputWorkers)
        t.join();
    timespec t2;
    clock_gettime(CLOCK_MONOTONIC, &t2);

    uint64_t usec = (t2.tv_sec * 1'000'000 + t2.tv_nsec / 1000) -
        (t1.tv_sec * 1'000'000 + t1.tv_nsec / 1000);
    std::cout << usec << " us" << std::endl;
    return 0;
}