Код
Я запускал свою программу 30 раз, и n перешел на run_and_join_threads(), изменив с 1 на 30 соответственно.
Обратите внимание, что jobs, переданные в run_and_join_threads(), заполнялись одинаково в каждом выполнении.
void do_job(JobQueue *jobs) {
Job job;
while (job = jobs->pop())
job();
// control flow goes here if jobs.pop() returns nullptr,
// which means all the jobs have been done
}
void run_and_join_threads(int n, JobQueue &jobs) {
vector<thread> threads;
threads.reserve(n);
for (int i = 0; i < n; ++i)
threads.push_back(thread(do_job, &jobs));
// synchronization
for (int i = 0; i < n; ++i)
threads[i].join();
}
JobQueue.h
#ifndef JOB_QUEUE_H
#define JOB_QUEUE_H
#include <functional>
#include <queue>
#include <mutex>
typedef std::function<void (void)> Job;
// Its methods are all atomic.
class JobQueue {
std::queue<Job> jobs;
std::mutex mtx;
public:
void push(Job job);
// pop removes the "oldest" job in the queue and returns it.
// pop returns nullptr if there's no more jobs left in the queue.
Job pop();
};
#endif
JobQueue.cc
#include "JobQueue.h"
using namespace std;
void JobQueue::push(Job job) {
mtx.lock();
jobs.push(job);
mtx.unlock();
}
Job JobQueue::pop() {
Job job = nullptr;
mtx.lock();
if (!jobs.empty()) {
job = jobs.front();
jobs.pop();
}
mtx.unlock();
return job;
}
Диаграмма
Я использую perf stat -e instructions:u ./my_program для записи количества команд во время выполнения моей программы.
Затем я обнаружил, что существует отрицательная корреляция между количеством потоков и количеством пользовательских инструкций.
Мои мысли
Поскольку «реальная задача» остается прежней, большее количество потоков должно привести к большему созданию и разрушению потоков, что приведет к большему количеству инструкций, но это не так из диаграммы. Я пытался гуглить с ключевыми словами в заголовке, но безуспешно.
опции компиляции: -std=c++14 -pthread -Wextra -Werror -MMD
версия gcc: 8.2.1 20180831
Выход --per-thread при n = 10
hw4-9525 8,524.37 msec task-clock:u # 0.153 CPUs utilized
hw4-9524 8,082.77 msec task-clock:u # 0.145 CPUs utilized
hw4-9522 7,824.93 msec task-clock:u # 0.140 CPUs utilized
hw4-9519 7,782.65 msec task-clock:u # 0.139 CPUs utilized
hw4-9518 7,734.42 msec task-clock:u # 0.138 CPUs utilized
hw4-9517 7,722.12 msec task-clock:u # 0.138 CPUs utilized
hw4-9520 7,636.99 msec task-clock:u # 0.137 CPUs utilized
hw4-9425 11,899.78 msec task-clock:u # 0.213 CPUs utilized
hw4-9521 7,585.14 msec task-clock:u # 0.136 CPUs utilized
hw4-9526 7,580.60 msec task-clock:u # 0.136 CPUs utilized
hw4-9523 7,306.57 msec task-clock:u # 0.131 CPUs utilized
hw4-9425 0 context-switches:u # 0.000 K/sec
hw4-9517 0 context-switches:u # 0.000 K/sec
hw4-9518 0 context-switches:u # 0.000 K/sec
hw4-9519 0 context-switches:u # 0.000 K/sec
hw4-9520 0 context-switches:u # 0.000 K/sec
hw4-9521 0 context-switches:u # 0.000 K/sec
hw4-9522 0 context-switches:u # 0.000 K/sec
hw4-9523 0 context-switches:u # 0.000 K/sec
hw4-9524 0 context-switches:u # 0.000 K/sec
hw4-9525 0 context-switches:u # 0.000 K/sec
hw4-9526 0 context-switches:u # 0.000 K/sec
hw4-9425 0 cpu-migrations:u # 0.000 K/sec
hw4-9517 0 cpu-migrations:u # 0.000 K/sec
hw4-9518 0 cpu-migrations:u # 0.000 K/sec
hw4-9519 0 cpu-migrations:u # 0.000 K/sec
hw4-9520 0 cpu-migrations:u # 0.000 K/sec
hw4-9521 0 cpu-migrations:u # 0.000 K/sec
hw4-9522 0 cpu-migrations:u # 0.000 K/sec
hw4-9523 0 cpu-migrations:u # 0.000 K/sec
hw4-9524 0 cpu-migrations:u # 0.000 K/sec
hw4-9525 0 cpu-migrations:u # 0.000 K/sec
hw4-9526 0 cpu-migrations:u # 0.000 K/sec
hw4-9425 9,332 page-faults:u # 1144.724 M/sec
hw4-9520 7,487 page-faults:u # 918.404 M/sec
hw4-9526 7,408 page-faults:u # 908.714 M/sec
hw4-9522 7,401 page-faults:u # 907.855 M/sec
hw4-9518 7,386 page-faults:u # 906.015 M/sec
hw4-9524 7,362 page-faults:u # 903.071 M/sec
hw4-9521 7,348 page-faults:u # 901.354 M/sec
hw4-9525 7,258 page-faults:u # 890.314 M/sec
hw4-9517 7,253 page-faults:u # 889.700 M/sec
hw4-9519 7,153 page-faults:u # 877.434 M/sec
hw4-9523 6,194 page-faults:u # 759.797 M/sec
hw4-9425 24,365,706,871 cycles:u # 2988857.145 GHz
hw4-9524 19,199,338,912 cycles:u # 2355116.623 GHz
hw4-9518 18,658,195,691 cycles:u # 2288736.452 GHz
hw4-9522 18,565,304,421 cycles:u # 2277341.801 GHz
hw4-9520 18,524,344,417 cycles:u # 2272317.378 GHz
hw4-9519 18,452,590,959 cycles:u # 2263515.629 GHz
hw4-9521 18,384,181,678 cycles:u # 2255124.099 GHz
hw4-9517 18,169,025,051 cycles:u # 2228731.578 GHz
hw4-9526 17,957,925,085 cycles:u # 2202836.674 GHz
hw4-9523 17,689,877,988 cycles:u # 2169956.262 GHz
hw4-9525 20,380,269,586 cycles:u # 2499977.312 GHz
hw4-9524 35,930,781,858 instructions:u # 1.88 insn per cycle
hw4-9425 31,238,610,254 instructions:u # 1.63 insn per cycle
hw4-9522 34,856,962,399 instructions:u # 1.82 insn per cycle
hw4-9518 34,794,129,974 instructions:u # 1.82 insn per cycle
hw4-9520 34,565,759,122 instructions:u # 1.81 insn per cycle
hw4-9519 34,521,122,564 instructions:u # 1.81 insn per cycle
hw4-9521 34,389,796,009 instructions:u # 1.80 insn per cycle
hw4-9517 33,823,905,990 instructions:u # 1.77 insn per cycle
hw4-9525 38,084,271,354 instructions:u # 1.99 insn per cycle
hw4-9526 33,682,632,175 instructions:u # 1.76 insn per cycle
hw4-9523 33,147,549,812 instructions:u # 1.73 insn per cycle
hw4-9525 6,113,561,884 branches:u # 749929530.566 M/sec
hw4-9425 5,978,592,665 branches:u # 733373322.423 M/sec
hw4-9524 5,765,141,950 branches:u # 707190060.107 M/sec
hw4-9522 5,593,987,998 branches:u # 686195195.687 M/sec
hw4-9518 5,583,032,551 branches:u # 684851328.824 M/sec
hw4-9520 5,546,955,396 branches:u # 680425868.769 M/sec
hw4-9519 5,541,456,246 branches:u # 679751307.023 M/sec
hw4-9521 5,518,407,713 branches:u # 676924023.050 M/sec
hw4-9517 5,427,113,316 branches:u # 665725254.544 M/sec
hw4-9526 5,407,241,325 branches:u # 663287626.012 M/sec
hw4-9523 5,318,730,317 branches:u # 652430286.226 M/sec
hw4-9525 66,142,537 branch-misses:u # 1.18% of all branches
hw4-9524 61,835,669 branch-misses:u # 1.10% of all branches
hw4-9518 61,243,167 branch-misses:u # 1.09% of all branches
hw4-9520 60,266,206 branch-misses:u # 1.07% of all branches
hw4-9521 59,396,966 branch-misses:u # 1.06% of all branches
hw4-9522 59,227,658 branch-misses:u # 1.05% of all branches
hw4-9519 59,210,503 branch-misses:u # 1.05% of all branches
hw4-9526 57,983,090 branch-misses:u # 1.03% of all branches
hw4-9517 57,910,215 branch-misses:u # 1.03% of all branches
hw4-9523 56,251,632 branch-misses:u # 1.00% of all branches
hw4-9425 32,626,137 branch-misses:u # 0.58% of all branches