From: Ross Bamford <rosco@...>
Date: 2006-01-11T08:28:04+09:00
Subject: Re: Finding CPU% of a linux task

On Tue, 10 Jan 2006 22:59:27 -0000, Joe Van Dyk <joevandyk@gmail.com>  
wrote:

> On 1/10/06, Barbier de Reuille Pierre <p.barbierdereuille@free.fr> wrote:
>> Well, on Linux 2.6, the list of the threads is in :
>>
>> /proc/[pid]/task
>>
>> But it is not true for Linux 2.4 :(
>> And on 2.4, I really don't know if you can tell a process from a thread
>> from the exterior. At least, I see no difference in the /proc virtual
>> system.
>
> For my purposes, I don't want to make a distinction between threads
> and processes.  I just want an accurate cpu percentage of a running
> program (which includes all of its threads and child processes).
>

Since you're looking in /proc anyway I guess this is for unixy systems, so  
_maybe_ the following is of use?

	module Process
	  class << self
	    def cpu_percent(pid)
	      pgid = getpgid(pid)
	      ps = `ps -Ao pcpu,pgrp`.to_a
	      (ps[1..-1]).inject(0.0) do |sum,s|
	        if s =~ /([\d.]+)\s*([\d]+)/
	          tcpu, tpgid = $~.captures
	          (tpgid.to_i == pgid) ? sum + tcpu.to_f: sum
	        end
	      end
	    end
	  end
	end

	pid = (ARGV[0] || Process.pid).to_i
	puts "#{pid}: #{Process.cpu_percent(pid)}"

Not a particularly clean one but maybe it gives a starting point? On my  
system a quick test gives:

	$ ps -o cmd,pcpu,pid,pgrp,sid
	CMD                         %CPU   PID  PGRP   SID
	bash                         0.0  4540  4540  4540
	ruby -e fork { loop do 1000  2.2  4942  4942  4540
	ruby -e fork { loop do 1000  4.3  4943  4942  4540
	ps -o cmd,pcpu,pid,pgrp,sid  0.0  5393  5393  4540

	$ ruby pinfo.rb 4942
	4942: 6.5%

	$ ruby pinfo.rb 4294
	pinfo.rb:4:in `getpgid': No such process (Errno::ESRCH)
	        from pinfo.rb:4:in `cpu_percent'
	        from pinfo.rb:17

(that second one is a deliberate example :) )

Check out 'man ps' for the different args etc, and the proper output  
format syntax if you're on non-GNU.

-- 
Ross Bamford - rosco@roscopeco.remove.co.uk