basic-profiling.rst

Basic kernel profiling
======================


These instructions are deliberately very basic. If you want something clever,
go read the real docs ;-)

Please don't add more stuff, but feel free to
correct my mistakes ;-)    (mbligh@aracnet.com)

Thanks to John Levon, Dave Hansen, et al. for help writing this.

``<test>`` is the thing you're trying to measure.
Make sure you have the correct ``System.map`` / ``vmlinux`` referenced!

It is probably easiest to use ``make install`` for linux and hack
``/sbin/installkernel`` to copy ``vmlinux`` to ``/boot``, in addition to
``vmlinuz``, ``config``, ``System.map``, which are usually installed by default.

Readprofile
-----------

A recent ``readprofile`` command is needed for 2.6, such as found in util-linux
2.12a, which can be downloaded from:

	http://www.kernel.org/pub/linux/utils/util-linux/

Most distributions will ship it already.

Add ``profile=2`` to the kernel command line.

Some ``readprofile`` commands::

	clear		readprofile -r
			<test>
	dump output	readprofile -m /boot/System.map > captured_profile

Oprofile
--------

Get the source (see Changes for required version) from
http://oprofile.sourceforge.net/ and add ``idle=poll`` to the kernel command
line.

Configure with ``CONFIG_PROFILING=y`` and ``CONFIG_OPROFILE=y`` & reboot on new kernel::

	./configure --with-kernel-support
	make install

For superior results, be sure to enable the local APIC. If opreport sees
a 0Hz CPU, APIC was not on. Be aware that idle=poll may mean a performance
penalty.

One time setup::

			opcontrol --setup --vmlinux=/boot/vmlinux

Some ``opcontrol`` commands::

	clear		opcontrol --reset
	start		opcontrol --start
		<test>
	stop		opcontrol --stop
	dump output	opreport >  output_file

To only report on the kernel, run ``opreport -l /boot/vmlinux > output_file``

A reset is needed to clear old statistics, which survive a reboot.