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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.
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