Linux内核的三种调度策略：
1，SCHED_OTHER 分时调度策略，
2，SCHED_FIFO实时调度策略，先到先服务。一旦占用cpu则一直运行。一直运行直到有更高优先级任务到达或自己放弃
3，SCHED_RR实时调度策略，时间片轮转。当进程的时间片用完，系统将重新分配时间片，并置于就绪队列尾。放在队列尾保证了所有具有相同优先级的RR任务的调度公平
Linux线程优先级设置
首先，可以通过以下两个函数来获得线程可以设置的最高和最低优先级，函数中的策略即上述三种策略的宏定义：
int sched_get_priority_max(int policy);
int sched_get_priority_min(int policy);
SCHED_OTHER是不支持优先级使用的，而SCHED_FIFO和SCHED_RR支持优先级的使用，他们分别为1和99，数值越大优先级越高。
设置和获取优先级通过以下两个函数
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int
pthread_attr_setschedparam
( pthread_attr_t
* attr, const
struct sched_param
* param) ;
int pthread_attr_getschedparam
( const pthread_attr_t
* attr,
struct sched_param * param)
;
param. sched_priority
= 51; //设置优先级
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系统创建线程时，默认的线程是SCHED_OTHER。所以如果我们要改变线程的调度策略的话，可以通过下面的这个函数实现。
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int
pthread_attr_setschedpolicy
( pthread_attr_t
* attr, int policy)
;
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上面的param使用了下面的这个数据结构：
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struct sched_param
{
int __sched_priority;
//所要设定的线程优先级
} ;
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我们可以通过下面的测试程序来说明，我们自己使用的系统的支持的优先级：
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#
include < stdio. h>
# include
< pthread. h>
# include
< sched. h>
# include
< assert . h>
static int get_thread_policy(
pthread_attr_t * attr)
{
int policy;
int rs =
pthread_attr_getschedpolicy ( attr,
& policy)
;
assert ( rs=
= 0)
;
switch ( policy)
{
case SCHED_FIFO:
printf (
"policy= SCHED_FIFO/n"
) ;
break ;
case SCHED_RR:
printf (
"policy= SCHED_RR"
) ;
break ;
case SCHED_OTHER:
printf (
"policy=SCHED_OTHER/n"
) ;
break ;
default :
printf (
"policy=UNKNOWN/n"
) ;
break ;
}
return policy;
}
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 ( rs=
= 0)
;
get_thread_policy( attr)
;
}
int main(
void )
{
pthread_attr_t attr;
struct sched_param sched;
int rs;
rs = pthread_attr_init
( & attr)
;
assert ( rs=
= 0)
;
int policy = get_thread_policy(
& attr)
;
printf (
"Show current configuration of priority/n" )
;
show_thread_priority(
& attr, policy)
;
printf (
"show SCHED_FIFO of priority/n" )
;
show_thread_priority(
& attr, SCHED_FIFO)
;
printf (
"show SCHED_RR of priority/n" )
;
show_thread_priority(
& attr, SCHED_RR)
;
printf (
"show priority of current thread/n" )
;
int priority = get_thread_priority(
& attr)
;
printf (
"Set thread policy/n" )
;
printf (
"set SCHED_FIFO policy/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, policy)
;
rs = pthread_attr_destroy
( & attr)
;
assert ( rs=
= 0)
;
return 0;
}
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下面是测试程序的运行结果：
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policy= SCHED_OTHER
Show current configuration of priority
max_priority= 0
min_priority= 0
show SCHED_FIFO of priority
max_priority= 99
min_priority= 1
show SCHED_RR of priority
max_priority= 99
min_priority= 1
show priority of current thread
priority= 0Set thread policy
set SCHED_FIFO policy
policy= SCHED_FIFO
set SCHED_RR policy
policy= SCHED_RRRestore current policy
policy= SCHED_OTHER
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