获取Android 的CPU的信息

在开发APP的时候，通常会有一些性能优化的内容。比如需要获取当前APP在运行中，占用CPU的比率多少；获取当前设备中的CPU的内核数、主频等信息，以用来衡量该机器的性能强弱；获取当前进程在系统中处于一种什么状态，当前进程被杀死或者被退出的状态等等。

此时需要读取到Android中的一些内存文件，类似于

/proc/[pid]/stat 文件（获取当前pid的状态，以及CPU耗时等等）
/sys/devices/system/cpu/cpufreq/policy0/cpuinfo_max_freq 文件（获取CPU的最大主频。在该文件夹 /sys/devices/system/cpu/cpufreq/policy0/ 中还有类似于这样的很多其他的文件，后续可以查看）

首先来了解一下 `/proc/[pid]/stat` 这个文件

该文件在ADB Shell中可以被读取到，其中的pid为进程的id。该文件下，是进程号为[pid]的一些基准信息，该文件被 ps 进行使用。该文件被定义在内核的文件中 fs/proc/array.c 。

在使用 cat /proc/[pid]/stat 命令读取该文件时，能够读取共有52个参数，其中的每一个参数都是使用空格(' ')进行分开。如下便是该文件的一些信息。

以下的英文注释该文件的出处为 proc(5)-Linux manual page 中文翻译为自译。

(1) pid  %d
       The process ID.

(2) comm  %s
       The filename of the executable, in parentheses.
       Strings longer than TASK_COMM_LEN (16) characters
       (including the terminating null byte) are silently
       truncated.  This is visible whether or not the
       executable is swapped out.

(3) state  %c
       One of the following characters, indicating process
       state:

       R  Running

       S  Sleeping in an interruptible wait

       D  Waiting in uninterruptible disk sleep

       Z  Zombie

       T  Stopped (on a signal) or (before Linux 2.6.33)
          trace stopped

       t  Tracing stop (Linux 2.6.33 onward)

       W  Paging (only before Linux 2.6.0)

       X  Dead (from Linux 2.6.0 onward)

       x  Dead (Linux 2.6.33 to 3.13 only)

       K  Wakekill (Linux 2.6.33 to 3.13 only)

       W  Waking (Linux 2.6.33 to 3.13 only)

       P  Parked (Linux 3.9 to 3.13 only)

(4) ppid  %d
       The PID of the parent of this process.

(5) pgrp  %d
       The process group ID of the process.

(6) session  %d
       The session ID of the process.

(7) tty_nr  %d
       The controlling terminal of the process.  (The
       minor device number is contained in the combination
       of bits 31 to 20 and 7 to 0; the major device
       number is in bits 15 to 8.)

(8) tpgid  %d
       The ID of the foreground process group of the
       controlling terminal of the process.

(9) flags  %u
       The kernel flags word of the process.  For bit
       meanings, see the PF_* defines in the Linux kernel
       source file include/linux/sched.h.  Details depend
       on the kernel version.

       The format for this field was %lu before Linux 2.6.

(10) minflt  %lu
       The number of minor faults the process has made
       which have not required loading a memory page from
       disk.

(11) cminflt  %lu
       The number of minor faults that the process's
       waited-for children have made.

(12) majflt  %lu
       The number of major faults the process has made
       which have required loading a memory page from
       disk.

(13) cmajflt  %lu
       The number of major faults that the process's
       waited-for children have made.

(14) utime  %lu
       Amount of time that this process has been scheduled
       in user mode, measured in clock ticks (divide by
       sysconf(_SC_CLK_TCK)).  This includes guest time,
       guest_time (time spent running a virtual CPU, see
       below), so that applications that are not aware of
       the guest time field do not lose that time from
       their calculations.

(15) stime  %lu
       Amount of time that this process has been scheduled
       in kernel mode, measured in clock ticks (divide by
       sysconf(_SC_CLK_TCK)).

(16) cutime  %ld
       Amount of time that this process's waited-for
       children have been scheduled in user mode, measured
       in clock ticks (divide by sysconf(_SC_CLK_TCK)).
       (See also times(2).)  This includes guest time,
       cguest_time (time spent running a virtual CPU, see
       below).

(17) cstime  %ld
       Amount of time that this process's waited-for
       children have been scheduled in kernel mode,
       measured in clock ticks (divide by
       sysconf(_SC_CLK_TCK)).

(18) priority  %ld
       (Explanation for Linux 2.6) For processes running a
       real-time scheduling policy (policy below; see
       sched_setscheduler(2)), this is the negated
       scheduling priority, minus one; that is, a number
       in the range -2 to -100, corresponding to real-time
       priorities 1 to 99.  For processes running under a
       non-real-time scheduling policy, this is the raw
       nice value (setpriority(2)) as represented in the
       kernel.  The kernel stores nice values as numbers
       in the range 0 (high) to 39 (low), corresponding to
       the user-visible nice range of -20 to 19.

       Before Linux 2.6, this was a scaled value based on
       the scheduler weighting given to this process.

(19) nice  %ld
       The nice value (see setpriority(2)), a value in the
       range 19 (low priority) to -20 (high priority).

(20) num_threads  %ld
       Number of threads in this process (since Linux
       2.6).  Before kernel 2.6, this field was hard coded
       to 0 as a placeholder for an earlier removed field.

(21) itrealvalue  %ld
       The time in jiffies before the next SIGALRM is sent
       to the process due to an interval timer.  Since
       kernel 2.6.17, this field is no longer maintained,
       and is hard coded as 0.

(22) starttime  %llu
       The time the process started after system boot.  In
       kernels before Linux 2.6, this value was expressed
       in jiffies.  Since Linux 2.6, the value is
       expressed in clock ticks (divide by
       sysconf(_SC_CLK_TCK)).

       The format for this field was %lu before Linux 2.6.

(23) vsize  %lu
       Virtual memory size in bytes.

(24) rss  %ld
       Resident Set Size: number of pages the process has
       in real memory.  This is just the pages which count
       toward text, data, or stack space.  This does not
       include pages which have not been demand-loaded in,
       or which are swapped out.  This value is
       inaccurate; see /proc/[pid]/statm below.

(25) rsslim  %lu
       Current soft limit in bytes on the rss of the
       process; see the description of RLIMIT_RSS in
       getrlimit(2).

(26) startcode  %lu  [PT]
       The address above which program text can run.

(27) endcode  %lu  [PT]
       The address below which program text can run.

(28) startstack  %lu  [PT]
       The address of the start (i.e., bottom) of the
       stack.

(29) kstkesp  %lu  [PT]
       The current value of ESP (stack pointer), as found
       in the kernel stack page for the process.

(30) kstkeip  %lu  [PT]
       The current EIP (instruction pointer).

(31) signal  %lu
       The bitmap of pending signals, displayed as a
       decimal number.  Obsolete, because it does not
       provide information on real-time signals; use
       /proc/[pid]/status instead.

(32) blocked  %lu
       The bitmap of blocked signals, displayed as a
       decimal number.  Obsolete, because it does not
       provide information on real-time signals; use
       /proc/[pid]/status instead.

(33) sigignore  %lu
       The bitmap of ignored signals, displayed as a
       decimal number.  Obsolete, because it does not
       provide information on real-time signals; use
       /proc/[pid]/status instead.

(34) sigcatch  %lu
       The bitmap of caught signals, displayed as a
       decimal number.  Obsolete, because it does not
       provide information on real-time signals; use
       /proc/[pid]/status instead.

(35) wchan  %lu  [PT]
       This is the "channel" in which the process is
       waiting.  It is the address of a location in the
       kernel where the process is sleeping.  The
       corresponding symbolic name can be found in
       /proc/[pid]/wchan.

(36) nswap  %lu
       Number of pages swapped (not maintained).

(37) cnswap  %lu
       Cumulative nswap for child processes (not
       maintained).

(38) exit_signal  %d  (since Linux 2.1.22)
       Signal to be sent to parent when we die.

(39) processor  %d  (since Linux 2.2.8)
       CPU number last executed on.

(40) rt_priority  %u  (since Linux 2.5.19)
       Real-time scheduling priority, a number in the
       range 1 to 99 for processes scheduled under a real-
       time policy, or 0, for non-real-time processes (see
       sched_setscheduler(2)).

(41) policy  %u  (since Linux 2.5.19)
       Scheduling policy (see sched_setscheduler(2)).
       Decode using the SCHED_* constants in
       linux/sched.h.

       The format for this field was %lu before Linux
       2.6.22.

(42) delayacct_blkio_ticks  %llu  (since Linux 2.6.18)
       Aggregated block I/O delays, measured in clock
       ticks (centiseconds).

(43) guest_time  %lu  (since Linux 2.6.24)
       Guest time of the process (time spent running a
       virtual CPU for a guest operating system), measured
       in clock ticks (divide by sysconf(_SC_CLK_TCK)).

(44) cguest_time  %ld  (since Linux 2.6.24)
       Guest time of the process's children, measured in
       clock ticks (divide by sysconf(_SC_CLK_TCK)).

(45) start_data  %lu  (since Linux 3.3)  [PT]
       Address above which program initialized and
       uninitialized (BSS) data are placed.

(46) end_data  %lu  (since Linux 3.3)  [PT]
       Address below which program initialized and
       uninitialized (BSS) data are placed.

(47) start_brk  %lu  (since Linux 3.3)  [PT]
       Address above which program heap can be expanded
       with brk(2).

(48) arg_start  %lu  (since Linux 3.5)  [PT]
       Address above which program command-line arguments
       (argv) are placed.

(49) arg_end  %lu  (since Linux 3.5)  [PT]
       Address below program command-line arguments (argv)
       are placed.

(50) env_start  %lu  (since Linux 3.5)  [PT]
       Address above which program environment is placed.

(51) env_end  %lu  (since Linux 3.5)  [PT]
       Address below which program environment is placed.

(52) exit_code  %d  (since Linux 3.5)  [PT]
       The thread's exit status in the form reported by
       waitpid(2).