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).
进程对CPU的占用率
当我们需要获取进程对CPU的占用率时，可以通过获取 /proc/[pid]/stat 文件，解析其中的参数进而进行计算得出。
计算的方法为: 进程CPU占用率 = （进程CPU时间2 - 进程CPU时间1） / （CPU总时间2 - CPU总时间1）
即：