ubuntu-phone team mailing list archive

[Thomas Voß <thomas.voss@xxxxxxxxxxxxx>]

On Wed, Sep 4, 2013 at 2:04 PM, John Lenton <john.lenton@xxxxxxxxxxxxx> wrote:
> On Wed, Sep 4, 2013 at 12:25 PM, Thomas Voß <thomas.voss@xxxxxxxxxxxxx> wrote:
>>
>> True, but to determine the CPU percentage, we would need to have the
>> CPU usage of all processes for a certain amount of time available.
>> That is, essentially parsing all of proc iiuc. I'm hopefully wrong,
>> but if not, could we resort to an approach that just considers the
>> per-process user and system CPU time consumed in a given time
>> interval?
>
> I might be missing something, but the load average (from
> /proc/loadavg) is the overall CPU usage for three given amounts of
> time (a minute, five minutes, fifteen minutes). Much faster than
> parsing all of proc:
>
>        /proc/loadavg
>               The first three fields in this file are  load  average
>               figures  giving  the  number  of jobs in the run queue
>               (state R) or waiting for disk I/O (state  D)  averaged
>               over  1,  5, and 15 minutes.  They are the same as the
>               load average numbers given by uptime(1) and other pro‐
>               grams.  The fourth field consists of two numbers sepa‐
>               rated by a slash (/).  The first of these is the  num‐
>               ber  of  currently runnable kernel scheduling entities
>               (processes, threads).  The value after  the  slash  is
>               the  number  of  kernel  scheduling entities that cur‐
>               rently exist on the system.  The fifth  field  is  the
>               PID  of  the process that was most recently created on
>               the system.
>
> (from 'man proc')

Sure, the load average is perfectly fine, but according to man proc,
/proc/$PID/stat has:

  utime %lu   (14)  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.

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

and we require the total CPU usage (in ticks) over all processes to
come up with the per-process percentage as I understand it. Or am I
missing something?

Thanks,

  Thomas