linux-kernel - Measuring startup-time from userspace

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Message-ID: <4D20FEF0.5020206@mozilla.com>
Date:	Sun, 02 Jan 2011 14:40:48 -0800
From:	Taras Glek <tglek@...illa.com>
To:	linux-kernel@...r.kernel.org
Subject: Measuring startup-time from userspace

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?
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