04.进程优先级与调度策略实战-CFANZ编程社区

linux内核的三种调度策略:

SCHED_OTHER分时调度策略
SCHED_FIFO实时调度策略,先到先服务
SHCED_RR实时调度策略(时间片轮转)

RR和FIFO属于实时任务,创建优先级大于0(1-99),按照可抢占优先级调度算法进行,就绪态的实时任务立即抢占非实时任务

主要是由下列2个函数可以获取线程设置的最高级和最低优先级

int sched_get_priority_max(int policy);	//获取实时优先级的最大值

int sched_get_priority_min(int policy);	//获取实时优先级的最大值

SCHED_OTHER它不支持优先级使用,SCHED_FIFO/SCHED_RR支持优先级使用,它们分别是1和99,数值越大优先级越高

实时调度策略(SCHED_FIFO/SCHED_RR) 优先级最大值为99

普通调度策略(SCHED_NORMAL/SCHED_BATCH/SCHED_IDLE),始终返回0,即普通任务调度的函数,没有效果

设备与获取优先级的两个主要函数:

int pthread_attr_setschedparam(pthread_attr_t *attr,const struct sched_param *param);//创建线程优先级

int pthread_attr_getschedparam(pthread_attr_t *attr,const struct sched_param *param);//获取线程优先级

param.sched_priority=51;//设置优先级

当系统创建线程时,默认线程是SCHED_OTHER,改变调度策略,可以通过以下的函数:

int pthread_attr_setschedpolicy(pthread_attr_t *attr,int policy);//设置线程调度策略

struct sched_param

{int __sched_priority;//所有设定的线程优先级}

实战

#include <stdio.h>
#include <pthread.h>
#include <sched.h>
#include <assert.h>

static int get_thread_policy(pthread_attr_t *attr)
{
    int plicy;
    int rs=pthread_attr_getschedpolicy(attr,&plicy);

    assert(rs==0); 

    switch(plicy)
    {
        case SCHED_FIFO:
        printf("policy=SCHED_FIFO.\n");
        break;

        case SCHED_RR:
        printf("policy=SCHED_RR.\n");
        break;

        case SCHED_OTHER:
        printf("policy=SCHED_OTHER.\n");
        break;

        default:
        printf("policy=UNKNOWN.\n");
        break;
    }

    return plicy;
}

static void show_thread_priority(pthread_attr_t *attr,int policy)
{
    int priority=sched_get_priority_max(policy); 
    assert(priority!=-1);
    printf("max_priority=%d\n",priority);

    priority=sched_get_priority_min(policy); 
    assert(priority!=-1);
    printf("min_priority=%d\n",priority);
}


static int get_thread_priority(pthread_attr_t *attr)
{
    struct sched_param param;
    int rs=pthread_attr_getschedparam(attr,&param);
    assert(rs==0);

    printf("priority=%d",param.__sched_priority);


    return param.__sched_priority;
}


static void set_thread_policy(pthread_attr_t *attr,int policy)
{
    int rs=pthread_attr_setschedpolicy(attr,policy);

    assert(0==rs);

    get_thread_policy(attr);

}

int main()
{
    pthread_attr_t attr;
    struct sched_param sched;

    int rs=pthread_attr_init(&attr);
    assert(0==rs);

    int plicy=get_thread_policy(&attr);
    printf("output current configuration of priority.\n");
    show_thread_priority(&attr,plicy);

    printf("output SCHED_FIFO of priority.\n");
    show_thread_priority(&attr,SCHED_FIFO);

    printf("output SCHED_RR of priority.\n");
    show_thread_priority(&attr,SCHED_RR);
    printf("output priority of current thread.\n");

    int priority=get_thread_priority(&attr);
    printf("set thrad policy.\n");
    printf("set SCHED_FIFO polity.\n");
    set_thread_policy(&attr,SCHED_FIFO); 

    printf("set SCHED_RR policy.\n");
    set_thread_policy(&attr,SCHED_RR); 
    printf("restore current policy.\n");
    set_thread_policy(&attr,plicy);

    rs=pthread_attr_destroy(&attr);c
    assert(0==rs);

    return 0;
}

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


void threadfunc1()
{
    sleep(1);
    int policy;
    struct sched_param praram;
    pthread_getschedparam(pthread_self(),&policy,&praram);

    if(policy==SCHED_OTHER)
    printf("SCHED_OTHER.\n");
    if(policy==SCHED_RR)
    ;
    printf("SCHED_RR 1.\n");
    if(policy==SCHED_FIFO)
    printf("SCHED_FIFO.\n");

    for(int i=1;i<=10;i++)
    {
        for(int j=1;j<4000000;j++){

        }
        printf("Threadfunc1.\n");
    }
    printf("pthreadfunc1 EXIT.\n");

}

void threadfunc2()
{
    sleep(1);
    int policy;
    struct sched_param praram;
    pthread_getschedparam(pthread_self(),&policy,&praram);

    if(policy==SCHED_OTHER)
    printf("SCHED_OTHER.\n");
    if(policy==SCHED_RR)
    ;
    printf("SCHED_RR 1.\n");
    if(policy==SCHED_FIFO)
    printf("SCHED_FIFO.\n");

    for(int i=1;i<=10;i++)
    {
        for(int j=1;j<4000000;j++){

        }
        printf("Threadfunc2.\n");
    }
    printf("pthreadfunc2 EXIT.\n");

    
}

void threadfunc3()
{
    sleep(1);
    int policy;
    struct sched_param praram;
    pthread_getschedparam(pthread_self(),&policy,&praram);

    if(policy==SCHED_OTHER)
    printf("SCHED_OTHER.\n");
    if(policy==SCHED_RR)
    ;
    printf("SCHED_RR 1.\n");
    if(policy==SCHED_FIFO)
    printf("SCHED_FIFO.\n");

    for(int i=1;i<=10;i++)
    {
        for(int j=1;j<4000000;j++){

        }
        printf("Threadfunc3.\n");
    }
    printf("pthreadfunc3 EXIT.\n");

    
}

int main()
{
    int i;
    i=getuid(); 

    if(i==0)
    printf("the current user is root.\n");
    else
    printf("the current user is not root.\n");

    pthread_t ppid1,ppid2,ppid3;
    struct sched_param param;

    pthread_attr_t attr1,attr2,attr3;

    pthread_attr_init(&attr2);
    pthread_attr_init(&attr1);
    pthread_attr_init(&attr3);

    param.sched_priority=51;

    pthread_attr_setschedpolicy(&attr3,SCHED_RR);
    pthread_attr_setschedparam(&attr3,&param);
    pthread_attr_setinheritsched(&attr3,PTHREAD_EXPLICIT_SCHED);

    param.sched_priority=22;
    pthread_attr_setschedpolicy(&attr2,SCHED_RR);
    pthread_attr_setschedparam(&attr2,&param);
    pthread_attr_setinheritsched(&attr2,PTHREAD_EXPLICIT_SCHED);

    pthread_create(&ppid3,&attr1,(void*)threadfunc3,NULL);
    pthread_create(&ppid2,&attr2,(void*)threadfunc2,NULL);
    pthread_create(&ppid1,&attr3,(void*)threadfunc1,NULL);

    pthread_join(ppid3,NULL);
    pthread_join(ppid2,NULL);
    pthread_join(ppid1,NULL);

    pthread_attr_destroy(&attr3);
    pthread_attr_destroy(&attr2);
    pthread_attr_destroy(&attr1);

    return 0;
}