CPU调度与上下文切换

// 调度器主函数
asmlinkage __visible void __sched schedule(void)
{
    struct task_struct *tsk = current;
    
    sched_submit_work(tsk);
    do {
        preempt_disable();
        __schedule(false);
        sched_preempt_enable_no_resched();
    } while (need_resched());
}

// 核心调度逻辑
static void __sched notrace __schedule(bool preempt)
{
    struct task_struct *prev, *next;
    unsigned long *switch_count;
    struct rq *rq;
    int cpu;

    cpu = smp_processor_id();
    rq = cpu_rq(cpu);
    prev = rq->curr;

    // 选择下一个要运行的进程
    next = pick_next_task(rq, prev, &rf);
    
    if (likely(prev != next)) {
        rq->nr_switches++;
        rq->curr = next;
        
        // 执行上下文切换
        rq = context_switch(rq, prev, next, &rf);
    }
}

static __always_inline struct rq *
context_switch(struct rq *rq, struct task_struct *prev,
               struct task_struct *next, struct rq_flags *rf)
{
    struct mm_struct *mm, *oldmm;
    
    prepare_task_switch(rq, prev, next);
    
    mm = next->mm;
    oldmm = prev->active_mm;
    
    // 切换内存空间
    if (!mm) {
        next->active_mm = oldmm;
        atomic_inc(&oldmm->mm_count);
        enter_lazy_tlb(oldmm, next);
    } else
        switch_mm_irqs_off(oldmm, mm, next);
    
    // 切换寄存器状态
    switch_to(prev, next, prev);
    
    return finish_task_switch(prev);
}

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <sched.h>

#define NUM_THREADS 100

void* worker(void* arg) {
    int id = *(int*)arg;
    
    // 设置CPU亲和性，强制在特定CPU上运行
    cpu_set_t cpuset;
    CPU_ZERO(&cpuset);
    CPU_SET(id % 2, &cpuset);  // 只在CPU 0和1之间切换
    
    if (pthread_setaffinity_np(pthread_self(), sizeof(cpu_set_t), &cpuset) != 0) {
        perror("pthread_setaffinity_np");
    }
    
    // 模拟工作负载
    for (int i = 0; i < 1000000; i++) {
        if (i % 100000 == 0) {
            printf("Thread %d: iteration %d\n", id, i);
        }
    }
    
    return NULL;
}

int main() {
    pthread_t threads[NUM_THREADS];
    int thread_ids[NUM_THREADS];
    
    // 创建多个线程
    for (int i = 0; i < NUM_THREADS; i++) {
        thread_ids[i] = i;
        if (pthread_create(&threads[i], NULL, worker, &thread_ids[i]) != 0) {
            perror("pthread_create");
            exit(1);
        }
    }
    
    // 等待所有线程完成
    for (int i = 0; i < NUM_THREADS; i++) {
        pthread_join(threads[i], NULL);
    }
    
    printf("All threads completed\n");
    return 0;
}

// cpu_intensive.c
#include <stdio.h>
#include <unistd.h>

int main() {
    int i = 0;
    while (1) {
        i++;
        if (i % 100000000 == 0) {
            printf("PID %d: iteration %d\n", getpid(), i);
        }
    }
    return 0;
}