Android中关于cpu/cpuset/schedtune的应

Android中关于cpu/cpuset/schedtune的应用都是基于进程优先级的，根据不同优先级划分进程类型。AMS(ActivityManagerService)和PMS(PackageManagerService)等通过class Process设置进程优先级、调度策略等；android/osProcess JNI通过调用libcutils.so/libutils.so执行getpriority/setpriority/sched_setscheduler/sched_getschedler系统调用或者直接操作CGroup文件节点以达到设置优先级，限制进程CPU资源的目的。

根据优先级，通过设置CGroup的cpu/cpuset/stune控制进程获得CPU执行时间、可调度CPU范围等，以达到对不同优先级进程的控制。

                                                  Android关于cpu/cpuset/schedtune的框架结构

Android关于cpu/cpuset/schedtune的框架结构

进程优先级和调度策略从上到下贯穿其中，但是在不同的层级的名称有一些变化。下面逐一介绍。

class Process以及android/os/Process JNI

frameworks/base/core/java/android/os/Process.java

其他服务通过class Process来设置进程优先级、调度侧率等。

class Process中优先级划分：

public static final int THREAD_PRIORITY_DEFAULT = 0; 应用的默认优先级

/*

* ***************************************

* ** Keep in sync with utils/threads.h **

* ***************************************

*/

public static final int THREAD_PRIORITY_LOWEST = 19; 线程的最低优先级

public static final int THREAD_PRIORITY_BACKGROUND = 10; 后台线程的默认优先级

public static final int THREAD_PRIORITY_FOREGROUND = -2; 前台进程的标准优先级

public static final int THREAD_PRIORITY_DISPLAY = -4; 系统用于显示功能的优先级

public static final int THREAD_PRIORITY_URGENT_DISPLAY = -8; 系统用于重要显示功能的优先级

public static final int THREAD_PRIORITY_AUDIO = -16; 音频线程默认优先级

public static final int THREAD_PRIORITY_URGENT_AUDIO = -19; 重要音频线程默认优先级

调度策略划分：

public static final int SCHED_OTHER = 0; 默认调度策略，对应CFS调度类

public static final int SCHED_FIFO = 1; FIFO调度策略，对应RT调度类

public static final int SCHED_RR = 2; RR调度策略，对应RT调度类

public static final int SCHED_BATCH = 3; 批调度策略，对应CFS调度类

public static final int SCHED_IDLE = 5; idle调度策略

class Process相关API，主要用于：

public static final native void setThreadPriority(int tid, int priority)

throws IllegalArgumentException, SecurityException;

public static final native void setThreadScheduler(int tid, int policy, int priority)

throws IllegalArgumentException;

public static final native void setThreadPriority(int tid, int priority)

throws IllegalArgumentException, SecurityException;

public static final native int getThreadPriority(int tid)

throws IllegalArgumentException;

public static final native int getThreadScheduler(int tid)

throws IllegalArgumentException;

public static final native void setThreadGroup(int tid, int group)

throws IllegalArgumentException, SecurityException;

public static final native void setProcessGroup(int pid, int group)

throws IllegalArgumentException, SecurityException;

frameworks/base/core/jni/android_util_Process.cpp

对应JNINativeMethod如下：

static const JNINativeMethod methods[] = {

…

{"setThreadPriority",   "(II)V", (void*)android_os_Process_setThreadPriority},

{"setThreadScheduler",  "(III)V", (void*)android_os_Process_setThreadScheduler},

{"setCanSelfBackground", "(Z)V", (void*)android_os_Process_setCanSelfBackground},

{"setThreadPriority",   "(I)V", (void*)android_os_Process_setCallingThreadPriority},

{"getThreadPriority",   "(I)I", (void*)android_os_Process_getThreadPriority},

{"getThreadScheduler",   "(I)I", (void*)android_os_Process_getThreadScheduler},

{"setThreadGroup",      "(II)V", (void*)android_os_Process_setThreadGroup},

{"setProcessGroup",     "(II)V", (void*)android_os_Process_setProcessGroup},

{"getProcessGroup",     "(I)I", (void*)android_os_Process_getProcessGroup},

…

};

scheduler相关API直接调用sched_setscheduler/sched_getscheduler。

libcutils.so/libutils.so

在介绍这个函数之前先介绍一下此处所使用的优先级定义，可以看出和class Process中是完全的对应关系：

ANDROID_PRIORITY_LOWEST         =  19,

/* use for background tasks */

ANDROID_PRIORITY_BACKGROUND     =  10,

/* most threads run at normal priority */

ANDROID_PRIORITY_NORMAL         =   0,

/* threads currently running a UI that the user is interacting with */

ANDROID_PRIORITY_FOREGROUND     =  -2,

/* the main UI thread has a slightly more favorable priority */

ANDROID_PRIORITY_DISPLAY        =  -4,

/* ui service treads might want to run at a urgent display (uncommon) */

ANDROID_PRIORITY_URGENT_DISPLAY =  HAL_PRIORITY_URGENT_DISPLAY,

/* all normal audio threads */

ANDROID_PRIORITY_AUDIO          = -16,

/* service audio threads (uncommon) */

ANDROID_PRIORITY_URGENT_AUDIO   = -19,

/* should never be used in practice. regular process might not

* be allowed to use this level */

ANDROID_PRIORITY_HIGHEST        = -20,

ANDROID_PRIORITY_DEFAULT        = ANDROID_PRIORITY_NORMAL,

还需要在研究一下，Sched Policy中使用的优先级映射关系：

/* Keep in sync with THREAD_GROUP_* in frameworks/base/core/java/android/os/Process.java */

typedef enum {

SP_DEFAULT    = -1,

SP_BACKGROUND = 0,

SP_FOREGROUND = 1,

SP_SYSTEM     = 2,  // can't be used with set_sched_policy()

SP_AUDIO_APP  = 3,

SP_AUDIO_SYS  = 4,

SP_TOP_APP    = 5,

SP_CNT,

SP_MAX        = SP_CNT - 1,

SP_SYSTEM_DEFAULT = SP_FOREGROUND,

} SchedPolicy;

Threads.cpp中定义了androidSetThreadPriority用于设置线程的优先级。

int androidSetThreadPriority(pid_t tid, int pri)

{

int rc = 0;

int lasterr = 0;

if (pri >= ANDROID_PRIORITY_BACKGROUND) { 如果priority大于等于BACKGROUND，则设置为BACKGROUND类型的调度策略。

rc = set_sched_policy(tid, SP_BACKGROUND);

} else if (getpriority(PRIO_PROCESS, tid) >= ANDROID_PRIORITY_BACKGROUND) { 如果priority小于BACKGROUND，且当线程为BACKGROUND类型，则设置为FOREGROUND类型。

rc = set_sched_policy(tid, SP_FOREGROUND);

}

if (rc) {

lasterr = errno;

}

if (setpriority(PRIO_PROCESS, tid, pri) < 0) { 设置优先级

rc = INVALID_OPERATION;

} else {

errno = lasterr;

}

return rc;

}

set_cpuset_policy根据SchedPolicy类型将tid写入cpuset和schedtune子系统中。

有下面的函数可以得出cpuset、schedtune和不同类型SchedPolicy之间的对应关系：

/dev/cpuset/foreground/tasks  SP_FOREGROUND SP_AUDIO_APP SP_AUDIO_SYS

/dev/cpuset/background/tasks  SP_BACKGROUND

/dev/cpuset/system-background/tasks  SP_SYSTEM

/dev/cpuset/top-app/tasks  SP_TOP_APP

/dev/stune/top-app/tasks  SP_TOP_APP

/dev/stune/foreground/tasks  SP_FOREGROUND SP_AUDIO_APP SP_AUDIO_SYS

/dev/stune/background/tasks  SP_BACKGROUND

int set_cpuset_policy(int tid, SchedPolicy policy)

{

// in the absence of cpusets, use the old sched policy

#ifndef USE_CPUSETS

return set_sched_policy(tid, policy);

#else

if (tid == 0) {

tid = gettid();

}

policy = _policy(policy);

pthread_once(&the_once, __initialize);

int fd = -1;

int boost_fd = -1;

switch (policy) {

case SP_BACKGROUND:

fd = bg_cpuset_fd;

boost_fd = bg_schedboost_fd;

break;

case SP_FOREGROUND:

case SP_AUDIO_APP:

case SP_AUDIO_SYS:

fd = fg_cpuset_fd;

boost_fd = fg_schedboost_fd;

break;

case SP_TOP_APP :

fd = ta_cpuset_fd;

boost_fd = ta_schedboost_fd;

break;

case SP_SYSTEM:

fd = system_bg_cpuset_fd;

break;

default:

boost_fd = fd = -1;

break;

}

if (add_tid_to_cgroup(tid, fd) != 0) {

if (errno != ESRCH && errno != ENOENT)

return -errno;

}

#ifdef USE_SCHEDBOOST

if (boost_fd > 0 && add_tid_to_cgroup(tid, boost_fd) != 0) {

if (errno != ESRCH && errno != ENOENT)

return -errno;

}

#endif

return 0;

#endif

}

set_sched_policy设置cpu/schedtune两个子系统，子系统节点和SchedPolicy类型对应如下：

/dev/cpuctl/tasks  SP_FOREGROUND SP_AUDIO_APP SP_AUDIO_SYS

/dev/cpuctl/bg_non_interactive/tasks  SP_BACKGROUND

/dev/stune/top-app/tasks  SP_TOP_APP

/dev/stune/foreground/tasks  SP_FOREGROUND SP_AUDIO_APP SP_AUDIO_SYS

/dev/stune/background/tasks  SP_BACKGROUND

int set_sched_policy(int tid, SchedPolicy policy)

{

if (tid == 0) {

tid = gettid();

}

policy = _policy(policy);

pthread_once(&the_once, __initialize);

#if POLICY_DEBUG

char statfile[64];

char statline[1024];

char thread_name[255];

snprintf(statfile, sizeof(statfile), "/proc/%d/stat", tid);

memset(thread_name, 0, sizeof(thread_name));

int fd = open(statfile, O_RDONLY | O_CLOEXEC);

if (fd >= 0) {

int rc = read(fd, statline, 1023);

close(fd);

statline[rc] = 0;

char *p = statline;

char *q;

for (p = statline; *p != '('; p++);

p++;

for (q = p; *q != ')'; q++);

strncpy(thread_name, p, (q-p));

}

switch (policy) {

case SP_BACKGROUND:

SLOGD("vvv tid %d (%s)", tid, thread_name);

break;

case SP_FOREGROUND:

case SP_AUDIO_APP:

case SP_AUDIO_SYS:

case SP_TOP_APP:

SLOGD("^^^ tid %d (%s)", tid, thread_name);

break;

case SP_SYSTEM:

SLOGD("/// tid %d (%s)", tid, thread_name);

break;

default:

SLOGD("??? tid %d (%s)", tid, thread_name);

break;

}

#endif

if (__sys_supports_schedgroups) { 是否使能schedtune CGroup

int fd = -1;

int boost_fd = -1;

switch (policy) {

case SP_BACKGROUND:

fd = bg_cgroup_fd;

boost_fd = bg_schedboost_fd;

break;

case SP_FOREGROUND:

case SP_AUDIO_APP:

case SP_AUDIO_SYS:

fd = fg_cgroup_fd;

boost_fd = fg_schedboost_fd;

break;

case SP_TOP_APP:

fd = fg_cgroup_fd;

boost_fd = ta_schedboost_fd;

break;

default:

fd = -1;

boost_fd = -1;

break;

}

if (add_tid_to_cgroup(tid, fd) != 0) {

if (errno != ESRCH && errno != ENOENT)

return -errno;

}

#ifdef USE_SCHEDBOOST

if (boost_fd > 0 && add_tid_to_cgroup(tid, boost_fd) != 0) {

if (errno != ESRCH && errno != ENOENT)

return -errno;

}

#endif

} else { 如果没有使能schedtune CGroup，则使用系统调用sched_setscheduler设置为SCHED_BATCH或者SCHED_NORMAL

struct sched_param param;

param.sched_priority = 0;

sched_setscheduler(tid,

(policy == SP_BACKGROUND) ?

SCHED_BATCH : SCHED_NORMAL,

¶m);

}

if (__sys_supports_timerslack) {

set_timerslack_ns(tid, policy == SP_BACKGROUND ?

TIMER_SLACK_BG : TIMER_SLACK_FG);

}

return 0;

}