Linux实时调度策略(SCHED_RR)和CFS(SCHED_OTHER)之间的区别

本文试图从直观角度，说明SCHED_RR调度策略和SCHED_OTHER调度策略之间的区别。

在Linux上，SCHED_OTHER和SCHED_NORMAL的意思相同，它们都是指的CFS调度策略，只不过，在内核中，CFS定义为SCHED_NORMAL，在用户态，CFS定义为SCHED_OTHER.

可参照内核头文件和musl libc头文件：

测试代码如下：

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

void *child_thread(void *arg)
{
	int policy = 0;
	int max_priority = 0,min_priority = 0;
	struct sched_param param;
	pthread_attr_t attr;
	struct sched_param sp;
	bzero((void*)&sp, sizeof(sp));
	 
	pthread_attr_init(&attr);
	pthread_attr_setinheritsched(&attr,PTHREAD_EXPLICIT_SCHED);
	pthread_attr_getinheritsched(&attr,&policy);

	if(policy == PTHREAD_EXPLICIT_SCHED){
		printf("Inheritsched:PTHREAD_EXPLICIT_SCHED\n");
	}

	if(policy == PTHREAD_INHERIT_SCHED){
		printf("Inheritsched:PTHREAD_INHERIT_SCHED\n");
	}
	 
	//pthread_attr_setschedpolicy(&attr,SCHED_RR);
	pthread_attr_setschedpolicy(&attr,SCHED_OTHER);
	pthread_attr_getschedpolicy(&attr,&policy);

	if(policy == SCHED_FIFO){
		printf("Schedpolicy:SCHED_FIFO\n");
	}
	if(policy == SCHED_RR){
		printf("Schedpolicy:SCHED_RR\n");
	}
	if(policy == SCHED_OTHER){
		printf("Schedpolicy:SCHED_OTHER\n");
	}

	max_priority = sched_get_priority_max(policy);
	min_priority = sched_get_priority_min(policy);
	printf("Maxpriority:%u\n",max_priority);
	printf("Minpriority:%u\n",min_priority);
	 
	param.sched_priority = max_priority;
	pthread_attr_setschedparam(&attr,&param);

	sp.sched_priority = 1;
	// Actually set the sched params for the current thread.
	if (0 == pthread_setschedparam(pthread_self(), policy, &sp)) {
		printf("IO Thread #%ld using high-pr