Profiling tool - How to use OProfile ?

OProfile can collect event information for the whole system in the background with very little overhead.
OProfile mainly consists of the opcontrol shell script and the oprofiled daemon.

The opcontrol script is used for configuring, starting, and stopping a profiling session, which are then recorded into sample files by oprofiled. And opreport is used to analyze these results.

Profiling setup parameters that you specify using opcontrol are cached in /root/.oprofile/daemonrc. Subsequent runs of opcontrol --start will continue to use these cached values until you override them with new values.

Creating profile Report:

Setup:
If you don't want to profile kernal we need to exclude it from the oprofile.
to do this we need to set --no-vimlinux to tell OProfile you don't have a vmlinux file

opcontrol --no-vmlinux

By default profile sample data is written to /var/lib/oprofile/samples. we can change this path using session-dir flag.

opcontrol --no-vmlinux --session-dir=/root/tmpsession

Run:
Now we need to start the daemon(oprofiled) which will collect the profile data.

opcontrol --start

Run your program. if it is an infinite process let it run in background and profile for as long as a time as possible.

Collect:
To collect that session profile data you can dump it using the command

opcontrol --dump

This ensures that any profile data collected by the oprofiled daemon has been flusehd to disk.(default: /var/lib/oprofile/samples) 

we can even save the session to the different files using --save flag
opcontrol --save <session_dir_name1>
opcontrol --save <session_dir_name2>

Stop:
When you want to stop profiling, you can do so with :

opcontrol --stop

But this will not kill the daemon this will give SIGHUP to oprofiled to stop collecting profile data.

to kill the daemon do this

opcontrol --shutdown

Analyzing profile data:

opreport is the tool that can be used to analyze the collected profile data.

opreport --long-filenames will show the whole summary of the system.

to analyze particular process during the specific time or session use

opreport -lg <process path> session:<saved session> 

opreport -lg /opt/bin/my_test_pgm session:saved_session_dir

-g : Show source file and line for each symbol

-l : List per-symbol information instead of a binary image summary

Comparing two profiles:

Often, we'd like to compare two profiles. when analyzing the performance of an application, we'd like to make code changes and examine the effect of the change. This is supported in opreport by giving a profile specification that identifies two different profiles.

opreport <shared-spec> { <first-profile> } { <second-profile> }

opreport  /opt/bin/my_test_pgn  { ./saved_session_1 } {} #empty brasses refers to current session.
or
opreport  /opt/bin/my_test_pgn  { ./saved_session_1 } { ./current_session }

 

This will create a %diff report.

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