如果在时间片结束时进程还在运行，则CPU将被剥夺并分配给另一个进程。如果进程在时间片结束前阻塞或结束，则CPU 当即进行切换

测试条件
单核CPU

示例代码

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <sys/time.h>

void time_print()
{
        struct timeval tv; 
        gettimeofday(&tv,NULL);
        printf("microsecond:%ld\n",tv.tv_sec*1000000 + tv.tv_usec);  //微秒
}

void *fun(void *arg)
{
        printf("I‘m thread, Thread ID = %lu\n", pthread_self());
        while(1)
        {   
                time_print();
                usleep(10);
        }   
        return NULL;
}

void *fun1(void *arg)
{
        printf("I‘m thread 1, Thread ID = %lu\n", pthread_self());
        while(1)
        {   
                sleep(1);
        }   
        return NULL;
}

int main()
{
        pthread_t tid;
        pthread_t tid1;

        pthread_create(&tid, NULL, fun, NULL);
        pthread_create(&tid, NULL, fun1, NULL);

        void *status;
        pthread_join(tid, &status);

        return 0;
}

效果

microsecond:1281790443
microsecond:1281790572
microsecond:1281790939
microsecond:1281791501
microsecond:1281791891
microsecond:1281792407
microsecond:1281792877
microsecond:1281793379
microsecond:1281793868
microsecond:1281794393
microsecond:1281794901
microsecond:1281795347
microsecond:1281795866
microsecond:1281796399
microsecond:1281796968
microsecond:1281797427
microsecond:1281797955
microsecond:1281798403
microsecond:1281798513
microsecond:1281798708
microsecond:1281798862
microsecond:1281799380
microsecond:1281799859
microsecond:1281800359
microsecond:1281800835
microsecond:1281801364
microsecond:1281801822
microsecond:1281802345
microsecond:1281802835
microsecond:1281803318
microsecond:1281803832
microsecond:1281804282
microsecond:1281804809
microsecond:1281805349

代码修改

void *fun1(void *arg)
{
        printf("I‘m thread 1, Thread ID = %lu\n", pthread_self());
        while(1)
        {   
                //sleep(1);
        }   
        return NULL;
}

效果

microsecond:2104360508
microsecond:2104360736
microsecond:2104360960
microsecond:2104361436
microsecond:2104361992
microsecond:2104362669
microsecond:2104366038
microsecond:2104366282
microsecond:2104367009
microsecond:2104367406
microsecond:2104367803
microsecond:2104368249
microsecond:2104368569
microsecond:2104369056
microsecond:2104369396
microsecond:2104369848
microsecond:2104370382
microsecond:2104371851
microsecond:2104375930
microsecond:2104376353
microsecond:2104376543
microsecond:2104377816

结论
通过第二个测试，可以看出时间片切换是ms级别的

如有错误，欢迎指正

linux时间片测试