source: doc/theses/thierry_delisle_PhD/code/prefetch.cpp @ 3b4750d

#include <algorithm>
#include <array>
#include <chrono>
#include <iostream>
#include <locale>
#include <memory>
#include <string>
#include <vector>

#include <cassert>

struct __attribute__((aligned(64))) element {
        size_t value;
};

using block = std::array<element, 100>;

block * create() {
        block * b = new block();
        for(auto & e : *b) {
                e.value = rand();
        }
        b->back().value = b->size();

        return b;
}

static inline size_t find(const block & b) {
        size_t r = 0;
        for(; r < b.size(); r++) {
                if(__builtin_expect(b[r].value == b.size(), false)) break;
        }

        return r;
}

void usage(char * argv[]) {
        std::cerr << argv[0] << ": [DURATION (FLOAT:SEC)] [NBLOCKS]" << std::endl;;
        std::exit(1);
}

int main(int argc, char * argv[]) {
        size_t nblocks = 1000;
        double duration = 5;

        std::cout.imbue(std::locale(""));

        switch (argc)
        {
        case 3:
                nblocks = std::stoul(argv[2]);
                [[fallthrough]];
        case 2:
                duration = std::stod(argv[1]);
                if( duration <= 0.0 ) {
                        std::cerr << "Duration must be positive, was " << argv[1] << "(" << duration << ")" << std::endl;
                        usage(argv);
                }
                [[fallthrough]];
        case 1:
                break;
        default:
                usage(argv);
                break;
        }

        std::vector<std::unique_ptr<block>> blocks;
        for(size_t i = 0; i < nblocks; i++) {
                blocks.emplace_back( create() );
        }
        std::random_shuffle(blocks.begin(), blocks.end());

        size_t CRC = 0;
        size_t count = 0;

        using clock = std::chrono::high_resolution_clock;
        auto before = clock::now();

        while(true) {
                for(const auto & b : blocks) {
                        CRC += find(*b);
                        count++;
                }
                auto now = clock::now();
                std::chrono::duration<double> durr = now - before;
                if( durr.count() > duration ) {
                        break;
                }
        }

        auto after = clock::now();
        std::chrono::duration<double> durr = after - before;
        duration = durr.count();

        using std::chrono::duration_cast;
        using std::chrono::nanoseconds;

        size_t ops_sec = size_t(double(count) / duration);
        auto dur_nano = duration_cast<nanoseconds>(std::chrono::duration<double>(1.0)).count();

        std::cout << "CRC           : " << CRC << "\n";
        std::cout << "Duration      : " << duration << "s\n";
        std::cout << "Total ops     : " << count << "\n";
        std::cout << "Ops/sec       : " << ops_sec << "\n";
        std::cout << "ns/Op         : " << ( dur_nano / ops_sec )<< "\n";
}