path: root/Documentation
diff options
Diffstat (limited to 'Documentation')
12 files changed, 472 insertions, 21 deletions
diff --git a/Documentation/DocBook/uio-howto.tmpl b/Documentation/DocBook/uio-howto.tmpl
index e3bb29a8d8d..c119484258b 100644
--- a/Documentation/DocBook/uio-howto.tmpl
+++ b/Documentation/DocBook/uio-howto.tmpl
@@ -133,10 +133,6 @@ interested in translating it, please email me
<para>updates of your driver can take place without recompiling
the kernel.</para>
- <para>if you need to keep some parts of your driver closed source,
- you can do so without violating the GPL license on the kernel.</para>
<sect1 id="how_uio_works">
diff --git a/Documentation/fb/pvr2fb.txt b/Documentation/fb/pvr2fb.txt
index 2bf6c2321c2..36bdeff585e 100644
--- a/Documentation/fb/pvr2fb.txt
+++ b/Documentation/fb/pvr2fb.txt
@@ -9,14 +9,13 @@ one found in the Dreamcast.
* It provides a nice large console (128 cols + 48 lines with 1024x768)
- without using tiny, unreadable fonts.
+ without using tiny, unreadable fonts (NOT on the Dreamcast)
* You can run XF86_FBDev on top of /dev/fb0
* Most important: boot logo :-)
- * Driver is currently limited to the Dreamcast PowerVR 2 implementation
- at the time of this writing.
+ * Driver is largely untested on non-Dreamcast systems.
@@ -29,11 +28,16 @@ Accepted options:
font:X - default font to use. All fonts are supported, including the
SUN12x22 font which is very nice at high resolutions.
-mode:X - default video mode. The following video modes are supported:
- 640x240-60, 640x480-60.
+mode:X - default video mode with format [xres]x[yres]-<bpp>@<refresh rate>
+ The following video modes are supported:
+ 640x640-16@60, 640x480-24@60, 640x480-32@60. The Dreamcast
+ defaults to 640x480-16@60. At the time of writing the
+ 24bpp and 32bpp modes function poorly. Work to fix that is
+ ongoing
Note: the 640x240 mode is currently broken, and should not be
- used for any reason. It is only mentioned as a reference.
+ used for any reason. It is only mentioned here as a reference.
inverse - invert colors on screen (for LCD displays)
@@ -52,10 +56,10 @@ output:X - output type. This can be any of the following: pal, ntsc, and
-XF86_FBDev should work, in theory. At the time of this writing it is
-totally untested and may or may not even portray the beginnings of
-working. If you end up testing this, please let me know!
+XF86_FBDev has been shown to work on the Dreamcast in the past - though not yet
+on any 2.6 series kernel.
Paul Mundt <lethal@linuxdc.org>
+Updated by Adrian McMenamin <adrian@mcmen.demon.co.uk>
diff --git a/Documentation/i386/zero-page.txt b/Documentation/i386/zero-page.txt
index 75b3680c41e..6c0817c4568 100644
--- a/Documentation/i386/zero-page.txt
+++ b/Documentation/i386/zero-page.txt
@@ -1,3 +1,13 @@
+The zero page is a kernel internal data structure, not a stable ABI. It might change
+without warning and the kernel has no way to detect old version of it.
+If you're writing some external code like a boot loader you should only use
+the stable versioned real mode boot protocol described in boot.txt. Otherwise the kernel
+might break you at any time.
Summary of boot_params layout (kernel point of view)
( collected by Hans Lermen and Martin Mares )
diff --git a/Documentation/kbuild/kconfig-language.txt b/Documentation/kbuild/kconfig-language.txt
index 536d5bfbdb8..fe8b0c4892c 100644
--- a/Documentation/kbuild/kconfig-language.txt
+++ b/Documentation/kbuild/kconfig-language.txt
@@ -98,6 +98,15 @@ applicable everywhere (see syntax).
times, the limit is set to the largest selection.
Reverse dependencies can only be used with boolean or tristate
+ Note:
+ select is evil.... select will by brute force set a symbol
+ equal to 'y' without visiting the dependencies. So abusing
+ select you are able to select a symbol FOO even if FOO depends
+ on BAR that is not set. In general use select only for
+ non-visible symbols (no promts anywhere) and for symbols with
+ no dependencies. That will limit the usefulness but on the
+ other hand avoid the illegal configurations all over. kconfig
+ should one day warn about such things.
- numerical ranges: "range" <symbol> <symbol> ["if" <expr>]
This allows to limit the range of possible input values for int
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index efdb42fd3fb..a326487a3ab 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1922,7 +1922,7 @@ and is between 256 and 4096 characters. It is defined in the file
See header of drivers/scsi/wd7000.c.
wdt= [WDT] Watchdog
- See Documentation/watchdog/watchdog.txt.
+ See Documentation/watchdog/wdt.txt.
xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
xd_geo= See header of drivers/block/xd.c.
diff --git a/Documentation/lguest/Makefile b/Documentation/lguest/Makefile
index 31e794ef5f9..c0b7a455639 100644
--- a/Documentation/lguest/Makefile
+++ b/Documentation/lguest/Makefile
@@ -13,7 +13,9 @@ LGUEST_GUEST_TOP := ($(CONFIG_PAGE_OFFSET) - 0x08000000)
CFLAGS:=-Wall -Wmissing-declarations -Wmissing-prototypes -O3 -Wl,-T,lguest.lds
+# Removing this works for some versions of ld.so (eg. Ubuntu Feisty) and
+# not others (eg. FC7).
all: lguest.lds lguest
# The linker script on x86 is so complex the only way of creating one
diff --git a/Documentation/memory-hotplug.txt b/Documentation/memory-hotplug.txt
new file mode 100644
index 00000000000..5fbcc22c98e
--- /dev/null
+++ b/Documentation/memory-hotplug.txt
@@ -0,0 +1,322 @@
+Memory Hotplug
+Last Updated: Jul 28 2007
+This document is about memory hotplug including how-to-use and current status.
+Because Memory Hotplug is still under development, contents of this text will
+be changed often.
+1. Introduction
+ 1.1 purpose of memory hotplug
+ 1.2. Phases of memory hotplug
+ 1.3. Unit of Memory online/offline operation
+2. Kernel Configuration
+3. sysfs files for memory hotplug
+4. Physical memory hot-add phase
+ 4.1 Hardware(Firmware) Support
+ 4.2 Notify memory hot-add event by hand
+5. Logical Memory hot-add phase
+ 5.1. State of memory
+ 5.2. How to online memory
+6. Logical memory remove
+ 6.1 Memory offline and ZONE_MOVABLE
+ 6.2. How to offline memory
+7. Physical memory remove
+8. Future Work List
+Note(1): x86_64's has special implementation for memory hotplug.
+ This text does not describe it.
+Note(2): This text assumes that sysfs is mounted at /sys.
+1. Introduction
+1.1 purpose of memory hotplug
+Memory Hotplug allows users to increase/decrease the amount of memory.
+Generally, there are two purposes.
+(A) For changing the amount of memory.
+ This is to allow a feature like capacity on demand.
+(B) For installing/removing DIMMs or NUMA-nodes physically.
+ This is to exchange DIMMs/NUMA-nodes, reduce power consumption, etc.
+(A) is required by highly virtualized environments and (B) is required by
+hardware which supports memory power management.
+Linux memory hotplug is designed for both purpose.
+1.2. Phases of memory hotplug
+There are 2 phases in Memory Hotplug.
+ 1) Physical Memory Hotplug phase
+ 2) Logical Memory Hotplug phase.
+The First phase is to communicate hardware/firmware and make/erase
+environment for hotplugged memory. Basically, this phase is necessary
+for the purpose (B), but this is good phase for communication between
+highly virtualized environments too.
+When memory is hotplugged, the kernel recognizes new memory, makes new memory
+management tables, and makes sysfs files for new memory's operation.
+If firmware supports notification of connection of new memory to OS,
+this phase is triggered automatically. ACPI can notify this event. If not,
+"probe" operation by system administration is used instead.
+(see Section 4.).
+Logical Memory Hotplug phase is to change memory state into
+avaiable/unavailable for users. Amount of memory from user's view is
+changed by this phase. The kernel makes all memory in it as free pages
+when a memory range is available.
+In this document, this phase is described as online/offline.
+Logical Memory Hotplug phase is triggred by write of sysfs file by system
+administrator. For the hot-add case, it must be executed after Physical Hotplug
+phase by hand.
+(However, if you writes udev's hotplug scripts for memory hotplug, these
+ phases can be execute in seamless way.)
+1.3. Unit of Memory online/offline operation
+Memory hotplug uses SPARSEMEM memory model. SPARSEMEM divides the whole memory
+into chunks of the same size. The chunk is called a "section". The size of
+a section is architecture dependent. For example, power uses 16MiB, ia64 uses
+1GiB. The unit of online/offline operation is "one section". (see Section 3.)
+To determine the size of sections, please read this file:
+This file shows the size of sections in byte.
+2. Kernel Configuration
+To use memory hotplug feature, kernel must be compiled with following
+config options.
+- For all memory hotplug
+ Memory model -> Sparse Memory (CONFIG_SPARSEMEM)
+ Allow for memory hot-add (CONFIG_MEMORY_HOTPLUG)
+- To enable memory removal, the followings are also necessary
+ Allow for memory hot remove (CONFIG_MEMORY_HOTREMOVE)
+ Page Migration (CONFIG_MIGRATION)
+- For ACPI memory hotplug, the followings are also necessary
+ Memory hotplug (under ACPI Support menu) (CONFIG_ACPI_HOTPLUG_MEMORY)
+ This option can be kernel module.
+- As a related configuration, if your box has a feature of NUMA-node hotplug
+ via ACPI, then this option is necessary too.
+ ACPI0004,PNP0A05 and PNP0A06 Container Driver (under ACPI Support menu)
+ This option can be kernel module too.
+3 sysfs files for memory hotplug
+All sections have their device information under /sys/devices/system/memory as
+(XXX is section id.)
+Now, XXX is defined as start_address_of_section / section_size.
+For example, assume 1GiB section size. A device for a memory starting at
+0x100000000 is /sys/device/system/memory/memory4
+(0x100000000 / 1Gib = 4)
+This device covers address range [0x100000000 ... 0x140000000)
+Under each section, you can see 3 files.
+'phys_index' : read-only and contains section id, same as XXX.
+'state' : read-write
+ at read: contains online/offline state of memory.
+ at write: user can specify "online", "offline" command
+'phys_device': read-only: designed to show the name of physical memory device.
+ This is not well implemented now.
+ These directories/files appear after physical memory hotplug phase.
+4. Physical memory hot-add phase
+4.1 Hardware(Firmware) Support
+On x86_64/ia64 platform, memory hotplug by ACPI is supported.
+In general, the firmware (ACPI) which supports memory hotplug defines
+memory class object of _HID "PNP0C80". When a notify is asserted to PNP0C80,
+Linux's ACPI handler does hot-add memory to the system and calls a hotplug udev
+script. This will be done automatically.
+But scripts for memory hotplug are not contained in generic udev package(now).
+You may have to write it by yourself or online/offline memory by hand.
+Please see "How to online memory", "How to offline memory" in this text.
+If firmware supports NUMA-node hotplug, and defines an object _HID "ACPI0004",
+"PNP0A05", or "PNP0A06", notification is asserted to it, and ACPI handler
+calls hotplug code for all of objects which are defined in it.
+If memory device is found, memory hotplug code will be called.
+4.2 Notify memory hot-add event by hand
+In some environments, especially virtualized environment, firmware will not
+notify memory hotplug event to the kernel. For such environment, "probe"
+interface is supported. This interface depends on CONFIG_ARCH_MEMORY_PROBE.
+Now, CONFIG_ARCH_MEMORY_PROBE is supported only by powerpc but it does not
+contain highly architecture codes. Please add config if you need "probe"
+Probe interface is located at
+You can tell the physical address of new memory to the kernel by
+% echo start_address_of_new_memory > /sys/devices/system/memory/probe
+Then, [start_address_of_new_memory, start_address_of_new_memory + section_size)
+memory range is hot-added. In this case, hotplug script is not called (in
+current implementation). You'll have to online memory by yourself.
+Please see "How to online memory" in this text.
+5. Logical Memory hot-add phase
+5.1. State of memory
+To see (online/offline) state of memory section, read 'state' file.
+% cat /sys/device/system/memory/memoryXXX/state
+If the memory section is online, you'll read "online".
+If the memory section is offline, you'll read "offline".
+5.2. How to online memory
+Even if the memory is hot-added, it is not at ready-to-use state.
+For using newly added memory, you have to "online" the memory section.
+For onlining, you have to write "online" to the section's state file as:
+% echo online > /sys/devices/system/memory/memoryXXX/state
+After this, section memoryXXX's state will be 'online' and the amount of
+available memory will be increased.
+Currently, newly added memory is added as ZONE_NORMAL (for powerpc, ZONE_DMA).
+This may be changed in future.
+6. Logical memory remove
+6.1 Memory offline and ZONE_MOVABLE
+Memory offlining is more complicated than memory online. Because memory offline
+has to make the whole memory section be unused, memory offline can fail if
+the section includes memory which cannot be freed.
+In general, memory offline can use 2 techniques.
+(1) reclaim and free all memory in the section.
+(2) migrate all pages in the section.
+In the current implementation, Linux's memory offline uses method (2), freeing
+all pages in the section by page migration. But not all pages are
+migratable. Under current Linux, migratable pages are anonymous pages and
+page caches. For offlining a section by migration, the kernel has to guarantee
+that the section contains only migratable pages.
+Now, a boot option for making a section which consists of migratable pages is
+supported. By specifying "kernelcore=" or "movablecore=" boot option, you can
+create ZONE_MOVABLE...a zone which is just used for movable pages.
+(See also Documentation/kernel-parameters.txt)
+Assume the system has "TOTAL" amount of memory at boot time, this boot option
+creates ZONE_MOVABLE as following.
+1) When kernelcore=YYYY boot option is used,
+ Size of memory not for movable pages (not for offline) is YYYY.
+ Size of memory for movable pages (for offline) is TOTAL-YYYY.
+2) When movablecore=ZZZZ boot option is used,
+ Size of memory not for movable pages (not for offline) is TOTAL - ZZZZ.
+ Size of memory for movable pages (for offline) is ZZZZ.
+Note) Unfortunately, there is no information to show which section belongs
+to ZONE_MOVABLE. This is TBD.
+6.2. How to offline memory
+You can offline a section by using the same sysfs interface that was used in
+memory onlining.
+% echo offline > /sys/devices/system/memory/memoryXXX/state
+If offline succeeds, the state of the memory section is changed to be "offline".
+If it fails, some error core (like -EBUSY) will be returned by the kernel.
+Even if a section does not belong to ZONE_MOVABLE, you can try to offline it.
+If it doesn't contain 'unmovable' memory, you'll get success.
+A section under ZONE_MOVABLE is considered to be able to be offlined easily.
+But under some busy state, it may return -EBUSY. Even if a memory section
+cannot be offlined due to -EBUSY, you can retry offlining it and may be able to
+offline it (or not).
+(For example, a page is referred to by some kernel internal call and released
+ soon.)
+Memory hotplug's design direction is to make the possibility of memory offlining
+higher and to guarantee unplugging memory under any situation. But it needs
+more work. Returning -EBUSY under some situation may be good because the user
+can decide to retry more or not by himself. Currently, memory offlining code
+does some amount of retry with 120 seconds timeout.
+7. Physical memory remove
+Need more implementation yet....
+ - Notification completion of remove works by OS to firmware.
+ - Guard from remove if not yet.
+8. Future Work
+ - allowing memory hot-add to ZONE_MOVABLE. maybe we need some switch like
+ sysctl or new control file.
+ - showing memory section and physical device relationship.
+ - showing memory section and node relationship (maybe good for NUMA)
+ - showing memory section is under ZONE_MOVABLE or not
+ - test and make it better memory offlining.
+ - support HugeTLB page migration and offlining.
+ - memmap removing at memory offline.
+ - physical remove memory.
diff --git a/Documentation/sched-design-CFS.txt b/Documentation/sched-design-CFS.txt
index 16feebb7bdc..84901e7c050 100644
--- a/Documentation/sched-design-CFS.txt
+++ b/Documentation/sched-design-CFS.txt
@@ -83,7 +83,7 @@ Some implementation details:
CFS uses nanosecond granularity accounting and does not rely on any
jiffies or other HZ detail. Thus the CFS scheduler has no notion of
'timeslices' and has no heuristics whatsoever. There is only one
- central tunable:
+ central tunable (you have to switch on CONFIG_SCHED_DEBUG):
diff --git a/Documentation/sched-nice-design.txt b/Documentation/sched-nice-design.txt
new file mode 100644
index 00000000000..e2bae5a577e
--- /dev/null
+++ b/Documentation/sched-nice-design.txt
@@ -0,0 +1,108 @@
+This document explains the thinking about the revamped and streamlined
+nice-levels implementation in the new Linux scheduler.
+Nice levels were always pretty weak under Linux and people continuously
+pestered us to make nice +19 tasks use up much less CPU time.
+Unfortunately that was not that easy to implement under the old
+scheduler, (otherwise we'd have done it long ago) because nice level
+support was historically coupled to timeslice length, and timeslice
+units were driven by the HZ tick, so the smallest timeslice was 1/HZ.
+In the O(1) scheduler (in 2003) we changed negative nice levels to be
+much stronger than they were before in 2.4 (and people were happy about
+that change), and we also intentionally calibrated the linear timeslice
+rule so that nice +19 level would be _exactly_ 1 jiffy. To better
+understand it, the timeslice graph went like this (cheesy ASCII art
+ A
+ \ | [timeslice length]
+ \ |
+ \ |
+ \ |
+ \ |
+ \|___100msecs
+ |^ . _
+ | ^ . _
+ | ^ . _
+ -*----------------------------------*-----> [nice level]
+ -20 | +19
+ |
+ |
+So that if someone wanted to really renice tasks, +19 would give a much
+bigger hit than the normal linear rule would do. (The solution of
+changing the ABI to extend priorities was discarded early on.)
+This approach worked to some degree for some time, but later on with
+HZ=1000 it caused 1 jiffy to be 1 msec, which meant 0.1% CPU usage which
+we felt to be a bit excessive. Excessive _not_ because it's too small of
+a CPU utilization, but because it causes too frequent (once per
+millisec) rescheduling. (and would thus trash the cache, etc. Remember,
+this was long ago when hardware was weaker and caches were smaller, and
+people were running number crunching apps at nice +19.)
+So for HZ=1000 we changed nice +19 to 5msecs, because that felt like the
+right minimal granularity - and this translates to 5% CPU utilization.
+But the fundamental HZ-sensitive property for nice+19 still remained,
+and we never got a single complaint about nice +19 being too _weak_ in
+terms of CPU utilization, we only got complaints about it (still) being
+too _strong_ :-)
+To sum it up: we always wanted to make nice levels more consistent, but
+within the constraints of HZ and jiffies and their nasty design level
+coupling to timeslices and granularity it was not really viable.
+The second (less frequent but still periodically occuring) complaint
+about Linux's nice level support was its assymetry around the origo
+(which you can see demonstrated in the picture above), or more
+accurately: the fact that nice level behavior depended on the _absolute_
+nice level as well, while the nice API itself is fundamentally
+ int nice(int inc);
+ asmlinkage long sys_nice(int increment)
+(the first one is the glibc API, the second one is the syscall API.)
+Note that the 'inc' is relative to the current nice level. Tools like
+bash's "nice" command mirror this relative API.
+With the old scheduler, if you for example started a niced task with +1
+and another task with +2, the CPU split between the two tasks would
+depend on the nice level of the parent shell - if it was at nice -10 the
+CPU split was different than if it was at +5 or +10.
+A third complaint against Linux's nice level support was that negative
+nice levels were not 'punchy enough', so lots of people had to resort to
+run audio (and other multimedia) apps under RT priorities such as
+SCHED_FIFO. But this caused other problems: SCHED_FIFO is not starvation
+proof, and a buggy SCHED_FIFO app can also lock up the system for good.
+The new scheduler in v2.6.23 addresses all three types of complaints:
+To address the first complaint (of nice levels being not "punchy"
+enough), the scheduler was decoupled from 'time slice' and HZ concepts
+(and granularity was made a separate concept from nice levels) and thus
+it was possible to implement better and more consistent nice +19
+support: with the new scheduler nice +19 tasks get a HZ-independent
+1.5%, instead of the variable 3%-5%-9% range they got in the old
+To address the second complaint (of nice levels not being consistent),
+the new scheduler makes nice(1) have the same CPU utilization effect on
+tasks, regardless of their absolute nice levels. So on the new
+scheduler, running a nice +10 and a nice 11 task has the same CPU
+utilization "split" between them as running a nice -5 and a nice -4
+task. (one will get 55% of the CPU, the other 45%.) That is why nice
+levels were changed to be "multiplicative" (or exponential) - that way
+it does not matter which nice level you start out from, the 'relative
+result' will always be the same.
+The third complaint (of negative nice levels not being "punchy" enough
+and forcing audio apps to run under the more dangerous SCHED_FIFO
+scheduling policy) is addressed by the new scheduler almost
+automatically: stronger negative nice levels are an automatic
+side-effect of the recalibrated dynamic range of nice levels.
diff --git a/Documentation/sysrq.txt b/Documentation/sysrq.txt
index ba328f25541..ef19142896c 100644
--- a/Documentation/sysrq.txt
+++ b/Documentation/sysrq.txt
@@ -1,6 +1,6 @@
Linux Magic System Request Key Hacks
Documentation for sysrq.c
-Last update: 2007-MAR-14
+Last update: 2007-AUG-04
* What is the magic SysRq key?
@@ -78,7 +78,7 @@ On all - write a character to /proc/sysrq-trigger. e.g.:
'g' - Used by kgdb on ppc and sh platforms.
'h' - Will display help (actually any other key than those listed
- above will display help. but 'h' is easy to remember :-)
+ here will display help. but 'h' is easy to remember :-)
'i' - Send a SIGKILL to all processes, except for init.
diff --git a/Documentation/thinkpad-acpi.txt b/Documentation/thinkpad-acpi.txt
index 6711fbcf408..eb2f5986e1e 100644
--- a/Documentation/thinkpad-acpi.txt
+++ b/Documentation/thinkpad-acpi.txt
@@ -105,10 +105,10 @@ The version of thinkpad-acpi's sysfs interface is exported by the driver
as a driver attribute (see below).
Sysfs driver attributes are on the driver's sysfs attribute space,
-for 2.6.20 this is /sys/bus/platform/drivers/thinkpad-acpi/.
+for 2.6.20 this is /sys/bus/platform/drivers/thinkpad_acpi/.
Sysfs device attributes are on the driver's sysfs attribute space,
-for 2.6.20 this is /sys/devices/platform/thinkpad-acpi/.
+for 2.6.20 this is /sys/devices/platform/thinkpad_acpi/.
Driver version
diff --git a/Documentation/vm/slabinfo.c b/Documentation/vm/slabinfo.c
index d4f21ffd140..1af7bd5a218 100644
--- a/Documentation/vm/slabinfo.c
+++ b/Documentation/vm/slabinfo.c
@@ -396,7 +396,7 @@ void report(struct slabinfo *s)
if (strcmp(s->name, "*") == 0)
- printf("\nSlabcache: %-20s Aliases: %2d Order : %2d Objects: %d\n",
+ printf("\nSlabcache: %-20s Aliases: %2d Order : %2d Objects: %lu\n",
s->name, s->aliases, s->order, s->objects);
if (s->hwcache_align)
printf("** Hardware cacheline aligned\n");