Measuring startup-time from userspace

Measuring startup-time from userspace

[Taras Glek]

Hi,
Does Linux provide a reasonable way to measure how long a process has 
existed for? The goal is to have a function that returns the number of 
milliseconds since process-creation.

We'd like to be able to have Firefox self-diagnose startup times. 
Unfortunately, it turns out that library loading time adds a lot to 
startup before application code runs, so a in-application timer would 
underestimate startup time.

It appears that the most precise solution is to read start time from 
/proc/self/stat. Unfortunately the time is in jiffies-since-startup and 
there don't seem to be any good counters to compare against (ie 
/proc/uptime doesn't provide enough resolution). So far the only 
workable solution seems to create a new thread/process. Then one can do 
(/proc/<newpid>/stat.starttime - /proc/self/stat.starttime) * 1000 / HZ
.

The question is, there way for a process to measure time-since-startup 
without horrible hacks like spawning a new processes?


Taras

ps. Perhaps /proc/timer_list contains enough info?

Re: Measuring startup-time from userspace

[Ben Gamari]

On Sun, 02 Jan 2011 14:40:48 -0800, Taras Glek <tglek@mozilla.com> wrote:
> The question is, there way for a process to measure time-since-startup 
> without horrible hacks like spawning a new processes?
> 
Would you consider an LD_PRELOAD library to fall into the "hack"
category? I'm not sure when .init section is executed, but it might be
substantially earlier than when _start() is called.

- Ben

Re: Measuring startup-time from userspace

[Alexander Clouter]

Taras Glek <tglek@mozilla.com> wrote:
>
> Does Linux provide a reasonable way to measure how long a process has 
> existed for? The goal is to have a function that returns the number of 
> milliseconds since process-creation.
>
At a glance:
----
alex@berk:~$ stat /proc/16863/
  File: `/proc/16863/'
  Size: 0               Blocks: 0          IO Block: 1024   directory
Device: 3h/3d   Inode: 837808      Links: 6
Access: (0555/dr-xr-xr-x)  Uid: ( 1000/    alex)   Gid: ( 1000/    alex)
Access: 2011-01-03 05:07:47.888363341 +0000
Modify: 2011-01-03 05:07:47.888363341 +0000
Change: 2011-01-03 05:07:47.888363341 +0000
----

A nanosecond resolution timestamp for the moment when the pid is created 
it seems.  I could be completely wrong, but this seems to be one of 
those "too easy to be true" moments.

Cheers

-- 
Alexander Clouter
.sigmonster says: Marriage is the sole cause of divorce.