Merge branch 'doc-tweaks' into docs-next

How to deal with bad memory e.g. reported by memtest86+ ?

=========================================================

March 2008

Jan-Simon Moeller, dl9pf@gmx.de

There are three possibilities I know of:

1) Reinsert/swap the memory modules

2) Buy new modules (best!) or try to exchange the memory

   if you have spare-parts

3) Use BadRAM or memmap

This Howto is about number 3) .

BadRAM

######

BadRAM is the actively developed and available as kernel-patch

here:  http://rick.vanrein.org/linux/badram/

For more details see the BadRAM documentation.

memmap

######

memmap is already in the kernel and usable as kernel-parameter at

boot-time.  Its syntax is slightly strange and you may need to

calculate the values by yourself!

Syntax to exclude a memory area (see admin-guide/kernel-parameters.rst for details)::

	memmap=<size>$<address>

Example: memtest86+ reported here errors at address 0x18691458, 0x18698424 and

some others. All had 0x1869xxxx in common, so I chose a pattern of

0x18690000,0xffff0000.

With the numbers of the example above::

	memmap=64K$0x18690000

or::

	memmap=0x10000$0x18690000

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.

Linux Kernel User's Documentation

=================================

The Linux kernel user's and administrator's guide

=================================================

Contents:

The following is a collection of user-oriented documents that have been

added to the kernel over time.  There is, as yet, little overall order or

organization here — this material was not written to be a single, coherent

document!  With luck things will improve quickly over time.

This initial section contains overall information, including the README

file describing the kernel as a whole, documentation on kernel parameters,

etc. 

.. toctree::

   :maxdepth: 2

   :numbered:

   :maxdepth: 1

   README

   kernel-parameters

   devices

Here is a set of documents aimed at users who are trying to track down

problems and bugs in particular.

.. toctree::

   :maxdepth: 1

   reporting-bugs

   security-bugs

   bug-hunting

   oops-tracing

   ramoops

   initrd

   init

   dynamic-debug-howto

   security-bugs

   kernel-parameters

   init

This is the beginning of a section with information of interest to

application developers.  Documents covering various aspects of the kernel

ABI will be found here.

.. toctree::

   :maxdepth: 1

   sysfs-rules

The rest of this manual consists of various unordered guides on how to

configure specific aspects of kernel behavior to your liking.

.. toctree::

   :maxdepth: 1

   initrd

   serial-console

   braille-console

   parport

   sysrq

   unicode

   vga-softcursor

   sysfs-rules

   devices

   binfmt-misc

   mono

   java

   bad-memory

   basic-profiling

.. only::  subproject and html

   =======

   * :ref:`genindex`

Kernel Parameters

~~~~~~~~~~~~~~~~~

The kernel's command-line parameters

====================================

The following is a consolidated list of the kernel parameters as

implemented by the __setup(), core_param() and module_param() macros

Rules on how to access information in the Linux kernel sysfs

============================================================

Rules on how to access information in sysfs

===========================================

The kernel-exported sysfs exports internal kernel implementation details

and depends on internal kernel structures and layout. It is agreed upon