Android中关于cpu/cpuset/schedtune的应用

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

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; }

 

上面的一系列转换可以用下图表示：

system\core\libcutils\Sched_policy.c中，对SP_*系列SchedPolicy转换成使用不同cpuctl、cpuset、stune句柄，将对应的pid、tid写入tasks中。
SP_BACKGROUND对应SCHED_BACH调度策略，其他对应SCHED_NORMAL。
SCHED_NORMAL：默认的调度策略，在旧版中为SCHED_OTHER。SCHED_BATCH：针对批处理进程。SCHED_IDLE：使用此调度侧率的进程优先级最低。
SCHED_NORMAL和SCHED_BATCH区别只是再唤醒时有区别，唤醒较频繁的进程不适合SCHED_BATCH。
如果使能__sys_supports_schedgroups，就不会调用sched_setscheduler去设置SchedulePolicy。

SCHED_NORMAL和SCHED_BACH区别

SP_BACKGROUND对应SCHED_BACH调度策略，其他对应SCHED_NORMAL。

SCHED_NORMAL：默认的调度策略，在旧版中为SCHED_OTHER。SCHED_BATCH：针对批处理进程。SCHED_IDLE：使用此调度侧率的进程优先级最低。

SCHED_NORMAL和SCHED_BATCH区别只是再唤醒时有区别，唤醒较频繁的进程不适合SCHED_BATCH。

如果使能__sys_supports_schedgroups，就不会调用sched_setscheduler去设置SchedulePolicy。

Android中的一个应用

cpu子系统：

# Create cgroup mount points for process groups mkdir /dev/cpuctl mount cgroup none /dev/cpuctl cpu chown system system /dev/cpuctl chown system system /dev/cpuctl/tasks chmod 0666 /dev/cpuctl/tasks write /dev/cpuctl/cpu.shares 1024 write /dev/cpuctl/cpu.rt_runtime_us 800000 write /dev/cpuctl/cpu.rt_period_us 1000000 mkdir /dev/cpuctl/bg_non_interactive chown system system /dev/cpuctl/bg_non_interactive/tasks chmod 0666 /dev/cpuctl/bg_non_interactive/tasks # 5.0 % write /dev/cpuctl/bg_non_interactive/cpu.shares 52 write /dev/cpuctl/bg_non_interactive/cpu.rt_runtime_us 700000 write /dev/cpuctl/bg_non_interactive/cpu.rt_period_us 1000000

cpuset子系统：

# sets up initial cpusets for ActivityManager mkdir /dev/cpuset mount cpuset none /dev/cpuset # this ensures that the cpusets are present and usable, but the device's # init.rc must actually set the correct cpus mkdir /dev/cpuset/foreground write /dev/cpuset/foreground/cpus 0 write /dev/cpuset/foreground/mems 0 mkdir /dev/cpuset/foreground/boost write /dev/cpuset/foreground/boost/cpus 0 write /dev/cpuset/foreground/boost/mems 0 mkdir /dev/cpuset/background write /dev/cpuset/background/cpus 0 write /dev/cpuset/background/mems 0 # system-background is for system tasks that should only run on # little cores, not on bigs # to be used only by init, so don't change system-bg permissions mkdir /dev/cpuset/system-background write /dev/cpuset/system-background/cpus 0 write /dev/cpuset/system-background/mems 0 mkdir /dev/cpuset/top-app write /dev/cpuset/top-app/cpus 0 write /dev/cpuset/top-app/mems 0 # change permissions for all cpusets we'll touch at runtime chown system system /dev/cpuset chown system system /dev/cpuset/foreground chown system system /dev/cpuset/foreground/boost chown system system /dev/cpuset/background chown system system /dev/cpuset/system-background chown system system /dev/cpuset/top-app chown system system /dev/cpuset/tasks chown system system /dev/cpuset/foreground/tasks chown system system /dev/cpuset/foreground/boost/tasks chown system system /dev/cpuset/background/tasks chown system system /dev/cpuset/system-background/tasks chown system system /dev/cpuset/top-app/tasks # set system-background to 0775 so SurfaceFlinger can touch it chmod 0775 /dev/cpuset/system-background chmod 0664 /dev/cpuset/foreground/tasks chmod 0664 /dev/cpuset/foreground/boost/tasks chmod 0664 /dev/cpuset/background/tasks chmod 0664 /dev/cpuset/system-background/tasks chmod 0664 /dev/cpuset/top-app/tasks chmod 0664 /dev/cpuset/tasks

schedtune子系统：

# Create energy-aware scheduler tuning nodes mkdir /dev/stune mount cgroup none /dev/stune schedtune mkdir /dev/stune/foreground chown system system /dev/stune chown system system /dev/stune/foreground chown system system /dev/stune/tasks chown system system /dev/stune/foreground/tasks chmod 0664 /dev/stune/tasks chmod 0664 /dev/stune/foreground/tasks