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https://github.com/gatieme/LDD-LinuxDeviceDrivers.git
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进程调度之优先级详解...
This commit is contained in:
gatieme
@@ -124,9 +124,12 @@ linux把进程区分为实时进程和非实时进程, 其中非实时进程进
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这需要与CPU的紧密交互. 每个进程刚好属于某一调度类, 各个调度类负责管理所属的进程. 通用调度器自身不涉及进程管理, 其工作都委托给调度器类.
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#优先级的内核表示
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##优先级的内核表示
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-------
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**linux优先级概述**
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>在用户空间通过nice命令设置进程的静态优先级, 这在内部会调用nice系统调用, 进程的nice值在-20~+19之间. 值越低优先级越高.
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>
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>setpriority系统调用也可以用来设置进程的优先级. 它不仅能够修改单个线程的优先级, 还能修改进程组中所有进程的优先级, 或者通过制定UID来修改特定用户的所有进程的优先级
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@@ -147,6 +150,10 @@ linux把进程区分为实时进程和非实时进程, 其中非实时进程进
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**内核的优先级表示**
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内核表示优先级的所有信息基本都放在[include/linux/sched/prio.h](http://lxr.free-electrons.com/source/include/linux/sched/prio.h?v=4.6)中, 其中定义了一些表示优先级的宏和函数,
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优先级数值通过宏来定义, 如下所示,
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其中MAX_NICE和MIN_NICE定义了nice的最大最小值
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@@ -159,20 +166,11 @@ linux把进程区分为实时进程和非实时进程, 其中非实时进程进
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#define MIN_NICE -20
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#define NICE_WIDTH (MAX_NICE - MIN_NICE + 1)
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/* http://lxr.free-electrons.com/source/include/linux/sched/prio.h?v=4.6#L21 */
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#define MAX_USER_RT_PRIO 100
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#define MAX_RT_PRIO MAX_USER_RT_PRIO
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/* http://lxr.free-electrons.com/source/include/linux/sched/prio.h?v=4.6#L24 */
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#define MAX_PRIO (MAX_RT_PRIO + 40)
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#define DEFAULT_PRIO (MAX_RT_PRIO + 20)
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```
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此外新版本的内核还引入了EDF实时调度算法, 它的优先级比RT进程和NORMAL/BATCH进程的优先级都要高, 因此内核将MAX_DL_PRIO设置为0, 可以参见内核文件[include/linux/sched/deadline.h](http://lxr.free-electrons.com/source/include/linux/sched/deadline.h)
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```c
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#define MAX_DL_PRIO 0
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````
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| 宏 | 值 | 描述 |
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| ------------- |:-------------:|:-------------:|
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@@ -186,6 +184,7 @@ linux把进程区分为实时进程和非实时进程, 其中非实时进程进
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而内核提供了一组宏将优先级在各种不同的表示形之间转移
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```c
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// http://lxr.free-electrons.com/source/include/linux/sched/prio.h?v=4.6#L27
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/*
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@@ -206,13 +205,43 @@ linux把进程区分为实时进程和非实时进程, 其中非实时进程进
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#define MAX_USER_PRIO (USER_PRIO(MAX_PRIO))
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```
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此外也提供了一些EDF调度算法的函数, 如下所示
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还有一些nice值和rlimit值之间相互转换的函数nice_to_rlimit和rlimit_to_nice, 这在nice系统调用进行检查的时候很有用, 他们定义在[include/linux/sched/prio.h, L47](http://lxr.free-electrons.com/source/include/linux/sched/prio.h#L47)中, 如下所示
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```c
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/*
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* Convert nice value [19,-20] to rlimit style value [1,40].
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*/
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static inline long nice_to_rlimit(long nice)
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{
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return (MAX_NICE - nice + 1);
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}
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/*
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* Convert rlimit style value [1,40] to nice value [-20, 19].
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*/
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static inline long rlimit_to_nice(long prio)
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{
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return (MAX_NICE - prio + 1);
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}
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```
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**DEF最早截至时间优先实时调度算法的优先级描述**
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此外新版本的内核还引入了EDF实时调度算法, 它的优先级比RT进程和NORMAL/BATCH进程的优先级都要高, 关于EDF的优先级的设置信息都早内核头文件[include/linux/sched/deadline.h](http://lxr.free-electrons.com/source/include/linux/sched/deadline.h?v=4.6#L10)
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因此内核将MAX_DL_PRIO设置为0, 可以参见内核文件[include/linux/sched/deadline.h](http://lxr.free-electrons.com/source/include/linux/sched/deadline.h?v=4.6#L10)
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```c
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#define MAX_DL_PRIO 0
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```
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此外也提供了一些EDF优先级处理所需的函数, 如下所示, 可以参见内核文件[include/linux/sched/deadline.h](http://lxr.free-electrons.com/source/include/linux/sched/deadline.h?v=4.6#L12)
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```c
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/* 判断一个优先级数值是不是EDF调度算法的优先级 */
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static inline int dl_prio(int prio)
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{
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/* 数组小于MAX_DL_PRIO的优先级就是EDF算法的优先级 */
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if (unlikely(prio < MAX_DL_PRIO))
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return 1;
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return 0;
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@@ -227,7 +256,7 @@ static inline bool dl_time_before(u64 a, u64 b)
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{
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return (s64)(a - b) < 0;
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}
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```
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````
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#进程的优先级表示
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@@ -34,6 +34,9 @@ linux优先级操作的系统调用有nice和getpriority, setpriority
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##优先级的内核表示
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-------
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**linux优先级概述**
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|
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>在用户空间通过nice命令设置进程的静态优先级, 这在内部会调用nice系统调用, 进程的nice值在-20~+19之间. 值越低优先级越高.
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>
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>setpriority系统调用也可以用来设置进程的优先级. 它不仅能够修改单个线程的优先级, 还能修改进程组中所有进程的优先级, 或者通过制定UID来修改特定用户的所有进程的优先级
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@@ -54,6 +57,10 @@ linux优先级操作的系统调用有nice和getpriority, setpriority
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**内核的优先级表示**
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内核表示优先级的所有信息基本都放在[include/linux/sched/prio.h](http://lxr.free-electrons.com/source/include/linux/sched/prio.h?v=4.6)中, 其中定义了一些表示优先级的宏和函数,
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优先级数值通过宏来定义, 如下所示,
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其中MAX_NICE和MIN_NICE定义了nice的最大最小值
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@@ -71,11 +78,6 @@ linux优先级操作的系统调用有nice和getpriority, setpriority
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#define DEFAULT_PRIO (MAX_RT_PRIO + 20)
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```
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此外新版本的内核还引入了EDF实时调度算法, 它的优先级比RT进程和NORMAL/BATCH进程的优先级都要高, 因此内核将MAX_DL_PRIO设置为0, 可以参见内核文件[include/linux/sched/deadline.h](http://lxr.free-electrons.com/source/include/linux/sched/deadline.h)
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```c
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#define MAX_DL_PRIO 0
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````
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| 宏 | 值 | 描述 |
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| ------------- |:-------------:|:-------------:|
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@@ -89,6 +91,7 @@ linux优先级操作的系统调用有nice和getpriority, setpriority
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而内核提供了一组宏将优先级在各种不同的表示形之间转移
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```c
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// http://lxr.free-electrons.com/source/include/linux/sched/prio.h?v=4.6#L27
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/*
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@@ -109,9 +112,59 @@ linux优先级操作的系统调用有nice和getpriority, setpriority
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#define MAX_USER_PRIO (USER_PRIO(MAX_PRIO))
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```
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此外也提供了一些EDF调度算法的函数, 如下所示, 可以参见内核文件[include/linux/sched/deadline.h](http://lxr.free-electrons.com/source/include/linux/sched/deadline.h)
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还有一些nice值和rlimit值之间相互转换的函数nice_to_rlimit和rlimit_to_nice, 这在nice系统调用进行检查的时候很有用, 他们定义在[include/linux/sched/prio.h, L47](http://lxr.free-electrons.com/source/include/linux/sched/prio.h#L47)中, 如下所示
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```c
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/*
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* Convert nice value [19,-20] to rlimit style value [1,40].
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*/
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static inline long nice_to_rlimit(long nice)
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{
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return (MAX_NICE - nice + 1);
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}
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/*
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* Convert rlimit style value [1,40] to nice value [-20, 19].
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*/
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static inline long rlimit_to_nice(long prio)
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{
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return (MAX_NICE - prio + 1);
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}
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```
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**DEF最早截至时间优先实时调度算法的优先级描述**
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此外新版本的内核还引入了EDF实时调度算法, 它的优先级比RT进程和NORMAL/BATCH进程的优先级都要高, 关于EDF的优先级的设置信息都早内核头文件[include/linux/sched/deadline.h](http://lxr.free-electrons.com/source/include/linux/sched/deadline.h?v=4.6#L10)
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因此内核将MAX_DL_PRIO设置为0, 可以参见内核文件[include/linux/sched/deadline.h](http://lxr.free-electrons.com/source/include/linux/sched/deadline.h?v=4.6#L10)
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```c
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#define MAX_DL_PRIO 0
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```
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此外也提供了一些EDF优先级处理所需的函数, 如下所示, 可以参见内核文件[include/linux/sched/deadline.h](http://lxr.free-electrons.com/source/include/linux/sched/deadline.h?v=4.6#L12)
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```c
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static inline int dl_prio(int prio)
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{
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if (unlikely(prio < MAX_DL_PRIO))
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return 1;
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return 0;
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}
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static inline int dl_task(struct task_struct *p)
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{
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return dl_prio(p->prio);
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}
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static inline bool dl_time_before(u64 a, u64 b)
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{
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return (s64)(a - b) < 0;
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}
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````
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##进程的优先级表示
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-------
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@@ -384,6 +437,24 @@ clamp_val宏定义在[include/linux/kernel.h, L757](http://lxr.free-electrons.co
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##can_nice
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-------
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can_nice可检查有没有nice的权限, 该函数定义在[kernel/sched/core.c, #L3544](http://lxr.free-electrons.com/source/kernel/sched/core.c?v=4.6#L3544)中, 如下所示
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```c
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/*
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* can_nice - check if a task can reduce its nice value
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* @p: task
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* @nice: nice value
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*/
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int can_nice(const struct task_struct *p, const int nice)
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{
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/* convert nice value [19,-20] to rlimit style value [1,40] */
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int nice_rlim = nice_to_rlimit(nice);
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return (nice_rlim <= task_rlimit(p, RLIMIT_NICE) ||
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capable(CAP_SYS_NICE));
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}
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```
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##security_task_setnice
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-------
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