Calculate CPU utilization give 2 readings.

Algorithm

user_util = 100 (utime_after - utime_before) / (time_total_after - time_total_before); sys_util = 100 (stime_after - stime_before) / (time_total_after - time_total_before);

Usage

iex> pid = CpuUtil.os_pid()
iex> cores = CpuUtil.num_cores()
iex> u1 = CpuUtil.pid_util(pid)
iex> Process.sleep(1000)
iex> u2 = CpuUtil.pid_util(pid)
iex> CpuUtil.calc_pid_util(u1, u2, cores)
%{
   user: 2.0,
   sys: 0.5,
   total: 2.5
}

References

• https://stackoverflow.com/questions/1420426/how-to-calculate-the-cpu-usage-of-a-process-by-pid-in-linux-from-c/1424556

Get the cup_util for the given os_pid and number of cores.

Blocks the calling process for time (1) seconds to collect the before and after samples.

Specs

getpid() :: integer()

Get the current OS PID

Specs

loadavg(integer()) :: binary()

Read the CPU's average load.

Specs

num_cores() :: {:ok, integer()} | :error

Get the number of CPU Cores.

Specs

pid_util(integer()) :: util_stat()

Get the current OS stat.

• Read the total time from /proc/stat
• Read the PID stats from /proc/<PID>/stat

Return a map:

%{
  total: integer()
  stats: proc_pid_stat()
}

Specs

stat() :: list() | {:error, any()}

Read the OS stat data.

• Reads /proc/stat
• Pareses the first line ('cpu')
• Converts the numbers (string) to integers

Specs

stat(binary()) :: list() | {:error, any()}

Specs

stat_pid(integer()) :: proc_pid_stat() | {:error, any()}

stat_pid(binary()) :: proc_pid_stat() | {:error, any()}

Get the current OS <PID> stat.

• Read /proc/<PID>/stat (single line of space separated fields)
• Parse the fields and convert and numbers (string) to integers

Returns a map of of the fields (atom keys) per the following definition:

• pid process id
• tcomm filename of the executable
• state state (R is running, S is sleeping, D is sleeping in an

•            uninterruptible wait, Z is zombie, T is traced or stopped)

• ppid process id of the parent process
• pgrp pgrp of the process
• sid session id
• tty_nr tty the process uses
• tty_pgrp pgrp of the tty
• flags task flags
• min_flt number of minor faults
• cmin_flt number of minor faults with child's
• maj_flt number of major faults
• cmaj_flt number of major faults with child's
• utime user mode jiffies
• stime kernel mode jiffies
• cutime user mode jiffies with child's
• cstime kernel mode jiffies with child's

Specs

stat_total_time(list()) :: integer()

Get the total_time from the given list.

Takes the output of CpuUtil.stat/0 and returns the total time.

Specs

total_time() :: integer()

Get the total_time.

Return the total time (from /proc/stat) as an integer.