CPU Affinity Masks(将线程放在不同的 CPU 上) [英] CPU Affinity Masks (Putting Threads on different CPUs)

问题描述

我有 4 个线程，我试图设置线程 1 在 CPU 1 上运行，线程 2 在 CPU 2 上运行，等等.但是，当我运行下面的代码时，关联掩码返回正确的值，但是当我对线程执行 sched_getcpu() 时，它们都返回它们在 CPU 4 上运行.

I have 4 threads, and I am trying to set thread 1 to run on CPU 1, thread 2 on CPU 2, etc. However, when I run my code below, the affinity masks are returning the correct values, but when I do a sched_getcpu() on the threads, they all return that they are running on CPU 4.

有人知道我的问题是什么吗?

Anybody know what my problem here is?

提前致谢！

#define _GNU_SOURCE
#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>
#include <sched.h>
#include <errno.h>

void *pthread_Message(char *message)
{
    printf("%s is running on CPU %d
", message, sched_getcpu());
}

int main()
{
    pthread_t thread1, thread2, thread3, thread4;
    pthread_t threadArray[4];
    cpu_set_t cpu1, cpu2, cpu3, cpu4;
    char *thread1Msg = "Thread 1";
    char *thread2Msg = "Thread 2";
    char *thread3Msg = "Thread 3";
    char *thread4Msg = "Thread 4";
    int thread1Create, thread2Create, thread3Create, thread4Create, i, temp;

    CPU_ZERO(&cpu1);
    CPU_SET(1, &cpu1);
    temp = pthread_setaffinity_np(thread1, sizeof(cpu_set_t), &cpu1);
    printf("Set returned by pthread_getaffinity_np() contained:
");
    for (i = 0; i < CPU_SETSIZE; i++)
        if (CPU_ISSET(i, &cpu1))
            printf("CPU1: CPU %d
", i);

    CPU_ZERO(&cpu2);
    CPU_SET(2, &cpu2);
    temp = pthread_setaffinity_np(thread2, sizeof(cpu_set_t), &cpu2);
    for (i = 0; i < CPU_SETSIZE; i++)
        if (CPU_ISSET(i, &cpu2))
            printf("CPU2: CPU %d
", i);

    CPU_ZERO(&cpu3);
    CPU_SET(3, &cpu3);
    temp = pthread_setaffinity_np(thread3, sizeof(cpu_set_t), &cpu3);
    for (i = 0; i < CPU_SETSIZE; i++)
        if (CPU_ISSET(i, &cpu3))
            printf("CPU3: CPU %d
", i);

    CPU_ZERO(&cpu4);
    CPU_SET(4, &cpu4);
    temp = pthread_setaffinity_np(thread4, sizeof(cpu_set_t), &cpu4);
    for (i = 0; i < CPU_SETSIZE; i++)
        if (CPU_ISSET(i, &cpu4))
            printf("CPU4: CPU %d
", i);

    thread1Create = pthread_create(&thread1, NULL, (void *)pthread_Message, thread1Msg);
    thread2Create = pthread_create(&thread2, NULL, (void *)pthread_Message, thread2Msg);
    thread3Create = pthread_create(&thread3, NULL, (void *)pthread_Message, thread3Msg);
    thread4Create = pthread_create(&thread4, NULL, (void *)pthread_Message, thread4Msg);

    pthread_join(thread1, NULL);
    pthread_join(thread2, NULL);
    pthread_join(thread3, NULL);
    pthread_join(thread4, NULL);

    return 0;
}

推荐答案

您正在尝试设置未初始化的线程的关联.

You're trying to set the affinity of threads that you did not initialize.

好的，让我给你一些更多的信息:

Ok, let me give you some more info:

不要混合线程句柄(您存储在 pthread_t 变量中的内容)和它们代表的内容(在某处运行的执行线程).您尝试做的是在线程启动之前使用需要线程对象的 API 设置线程的属性.碰巧 pthread_create 创建对象并同时开始执行，因此尝试使用 pthread_setaffinity_np 并不是正确的方法(如果您想更改 当前正在运行的线程的亲和性).

Don't mix thread handles (the thing you store in the pthread_t variable) and what they represent (a thread of execution that runs somewhere). What you were trying to do is to set a property of a thread before it starts, with an API that requires the thread object. As it happens pthread_create creates the object and starts the execution at the same time, so trying to use pthread_setaffinity_np is not the right way to go (this is useful if you want to change the affinity of a currently running thread).

但是... pthread_create 有一个属性参数(您将 NULL 传递给它).这是存储您希望如何创建线程的信息.

But... pthread_create has an attribute parameter (you're passing NULL to it). This is storing the information of how you want the thread to be created.

亲和力是您可以通过该参数设置的属性之一.请参阅pthread_attr_init<的手册页文档/a> 和 pthread_attr_setaffinity_np究竟如何

Affinity is one of the attributes you can set through that parameter. See the man-page documentation for pthread_attr_init and pthread_attr_setaffinity_np for how exactly

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