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Page replacement is handled in the Linux Kernel in one of two ways:
1) Asynchronously via kswapd
2) Synchronously, via direct reclaim
At page allocation time the allocating task is immediately given a page
from the zone free list allowing it to go right back to work doing
whatever it was doing; Probably directly or indirectly executing business
logic.
Just prior to satisfying the allocation, free pages is checked to see if
it has reached the zone low watermark and if so, kswapd is awakened.
Kswapd will start scanning pages looking for inactive pages to evict to
make room for new page allocations. The work of kswapd allows tasks to
continue allocating memory from their respective zone free list without
incurring any delay.
When the demand for free pages exceeds the rate that kswapd tasks can
supply them, page allocation works differently. Once the allocating task
finds that the number of free pages is at or below the zone min watermark,
the task will no longer pull pages from the free list. Instead, the task
will run the same CPU-bound routines as kswapd to satisfy its own
allocation by scanning and evicting pages. This is called a direct reclaim.
The time spent performing a direct reclaim can be substantial, often
taking tens to hundreds of milliseconds for small order0 allocations to
half a second or more for order9 huge-page allocations. In fact, kswapd is
not actually required on a linux system. It exists for the sole purpose of
optimizing performance by preventing direct reclaims.
When memory shortfall is sufficient to trigger direct reclaims, they can
occur in any task that is running on the system. A single aggressive
memory allocating task can set the stage for collateral damage to occur in
small tasks that rarely allocate additional memory. Consider the impact of
injecting an additional 100ms of latency when nscd allocates memory to
facilitate caching of a DNS query.
The presence of direct reclaims 10 years ago was a fairly reliable
indicator that too much was being asked of a Linux system. Kswapd was
likely wasting time scanning pages that were ineligible for eviction.
Adding RAM or reducing the working set size would usually make the problem
go away. Since then hardware has evolved to bring a new struggle for
kswapd. Storage speeds have increased by orders of magnitude while CPU
clock speeds stayed the same or even slowed down in exchange for more
cores per package. This presents a throughput problem for a single
threaded kswapd that will get worse with each generation of new hardware.
Test Details
NOTE: The tests below were run with shadow entries disabled. See the
associated patch and cover letter for details
The tests below were designed with the assumption that a kswapd bottleneck
is best demonstrated using filesystem reads. This way, the inactive list
will be full of clean pages, simplifying the analysis and allowing kswapd
to achieve the highest possible steal rate. Maximum steal rates for kswapd
are likely to be the same or lower for any other mix of page types on the
system.
Tests were run on a 2U Oracle X7-2L with 52 Intel Xeon Skylake 2GHz cores,
756GB of RAM and 8 x 3.6 TB NVMe Solid State Disk drives. Each drive has
an XFS file system mounted separately as /d0 through /d7. SSD drives
require multiple concurrent streams to show their potential, so I created
eleven 250GB zero-filled files on each drive so that I could test with
parallel reads.
The test script runs in multiple stages. At each stage, the number of dd
tasks run concurrently is increased by 2. I did not include all of the
test output for brevity.
During each stage dd tasks are launched to read from each drive in a round
robin fashion until the specified number of tasks for the stage has been
reached. Then iostat, vmstat and top are started in the background with 10
second intervals. After five minutes, all of the dd tasks are killed and
the iostat, vmstat and top output is parsed in order to report the
following:
CPU consumption
- sy - aggregate kernel mode CPU consumption from vmstat output. The value
doesn't tend to fluctuate much so I just grab the highest value.
Each sample is averaged over 10 seconds
- dd_cpu - for all of the dd tasks averaged across the top samples since
there is a lot of variation.
Throughput
- in Kbytes
- Command is iostat -x -d 10 -g total
This first test performs reads using O_DIRECT in order to show the maximum
throughput that can be obtained using these drives. It also demonstrates
how rapidly throughput scales as the number of dd tasks are increased.
The dd command for this test looks like this:
Command Used: dd iflag=direct if=/d${i}/$n of=/dev/null bs=4M
Test #1: Direct IO
dd sy dd_cpu throughput
6 0 2.33 14726026.40
10 1 2.95 19954974.80
16 1 2.63 24419689.30
22 1 2.63 25430303.20
28 1 2.91 26026513.20
34 1 2.53 26178618.00
40 1 2.18 26239229.20
46 1 1.91 26250550.40
52 1 1.69 26251845.60
58 1 1.54 26253205.60
64 1 1.43 26253780.80
70 1 1.31 26254154.80
76 1 1.21 26253660.80
82 1 1.12 26254214.80
88 1 1.07 26253770.00
90 1 1.04 26252406.40
Throughput was close to peak with only 22 dd tasks. Very little system CPU
was consumed as expected as the drives DMA directly into the user address
space when using direct IO.
In this next test, the iflag=direct option is removed and we only run the
test until the pgscan_kswapd from /proc/vmstat starts to increment. At
that point metrics are parsed and reported and the pagecache contents are
dropped prior to the next test. Lather, rinse, repeat.
Test #2: standard file system IO, no page replacement
dd sy dd_cpu throughput
6 2 28.78 5134316.40
10 3 31.40 8051218.40
16 5 34.73 11438106.80
22 7 33.65 14140596.40
28 8 31.24 16393455.20
34 10 29.88 18219463.60
40 11 28.33 19644159.60
46 11 25.05 20802497.60
52 13 26.92 22092370.00
58 13 23.29 22884881.20
64 14 23.12 23452248.80
70 15 22.40 23916468.00
76 16 22.06 24328737.20
82 17 20.97 24718693.20
88 16 18.57 25149404.40
90 16 18.31 25245565.60
Each read has to pause after the buffer in kernel space is populated while
those pages are added to the pagecache and copied into the user address
space. For this reason, more parallel streams are required to achieve peak
throughput. The copy operation consumes substantially more CPU than direct
IO as expected.
The next test measures throughput after kswapd starts running. This is the
same test only we wait for kswapd to wake up before we start collecting
metrics. The script actually keeps track of a few things that were not
mentioned earlier. It tracks direct reclaims and page scans by watching
the metrics in /proc/vmstat. CPU consumption for kswapd is tracked the
same way it is tracked for dd.
Since the test is 100% reads, you can assume that the page steal rate for
kswapd and direct reclaims is almost identical to the scan rate.
Test #3: 1 kswapd thread per node
dd sy dd_cpu kswapd0 kswapd1 throughput dr pgscan_kswapd pgscan_direct
10 4 26.07 28.56 27.03 7355924.40 0 459316976 0
16 7 34.94 69.33 69.66 10867895.20 0 872661643 0
22 10 36.03 93.99 99.33 13130613.60 489 1037654473 11268334
28 10 30.34 95.90 98.60 14601509.60 671 1182591373 15429142
34 14 34.77 97.50 99.23 16468012.00 10850 1069005644 249839515
40 17 36.32 91.49 97.11 17335987.60 18903 975417728 434467710
46 19 38.40 90.54 91.61 17705394.40 25369 855737040 582427973
52 22 40.88 83.97 83.70 17607680.40 31250 709532935 724282458
58 25 40.89 82.19 80.14 17976905.60 35060 657796473 804117540
64 28 41.77 73.49 75.20 18001910.00 39073 561813658 895289337
70 33 45.51 63.78 64.39 17061897.20 44523 379465571 1020726436
76 36 46.95 57.96 60.32 16964459.60 47717 291299464 1093172384
82 39 47.16 55.43 56.16 16949956.00 49479 247071062 1134163008
88 42 47.41 53.75 47.62 16930911.20 51521 195449924 1180442208
90 43 47.18 51.40 50.59 16864428.00 51618 190758156 1183203901
In the previous test where kswapd was not involved, the system-wide kernel
mode CPU consumption with 90 dd tasks was 16%. In this test CPU consumption
with 90 tasks is at 43%. With 52 cores, and two kswapd tasks (one per NUMA
node), kswapd can only be responsible for a little over 4% of the increase.
The rest is likely caused by 51,618 direct reclaims that scanned 1.2
billion pages over the five minute time period of the test.
Same test, more kswapd tasks:
Test #4: 4 kswapd threads per node
dd sy dd_cpu kswapd0 kswapd1 throughput dr pgscan_kswapd pgscan_direct
10 5 27.09 16.65 14.17 7842605.60 0 459105291 0
16 10 37.12 26.02 24.85 11352920.40 15 920527796 358515
22 11 36.94 37.13 35.82 13771869.60 0 1132169011 0
28 13 35.23 48.43 46.86 16089746.00 0 1312902070 0
34 15 33.37 53.02 55.69 18314856.40 0 1476169080 0
40 19 35.90 69.60 64.41 19836126.80 0 1629999149 0
46 22 36.82 88.55 57.20 20740216.40 0 1708478106 0
52 24 34.38 93.76 68.34 21758352.00 0 1794055559 0
58 24 30.51 79.20 82.33 22735594.00 0 1872794397 0
64 26 30.21 97.12 76.73 23302203.60 176 1916593721 4206821
70 33 32.92 92.91 92.87 23776588.00 3575 1817685086 85574159
76 37 31.62 91.20 89.83 24308196.80 4752 1812262569 113981763
82 29 25.53 93.23 92.33 24802791.20 306 2032093122 7350704
88 43 37.12 76.18 77.01 25145694.40 20310 1253204719 487048202
90 42 38.56 73.90 74.57 22516787.60 22774 1193637495 545463615
By increasing the number of kswapd threads, throughput increased by ~50%
while kernel mode CPU utilization decreased or stayed the same, likely due
to a decrease in the number of parallel tasks at any given time doing page
replacement.
Signed-off-by: Buddy Lumpkin <buddy.lumpkin@oracle.com>
Bug: 171351667
Link: https://lore.kernel.org/lkml/1522661062-39745-1-git-send-email-buddy.lumpkin@oracle.com
[charante@codeaurora.org]: Changes made to select number of kswapds through uapi
Change-Id: I8425cab7f40cbeaf65af0ea118c1a9ac7da0930e
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>
|
||
|---|---|---|
| .. | ||
| acpi | ||
| aoe | ||
| auxdisplay | ||
| blockdev | ||
| cgroup-v1 | ||
| cifs | ||
| device-mapper | ||
| gpio | ||
| hw-vuln | ||
| kdump | ||
| laptops | ||
| LSM | ||
| media | ||
| mm | ||
| namespaces | ||
| nfs | ||
| perf | ||
| pm | ||
| sysctl | ||
| wimax | ||
| abi-obsolete.rst | ||
| abi-removed.rst | ||
| abi-stable.rst | ||
| abi-testing.rst | ||
| abi.rst | ||
| bcache.rst | ||
| binderfs.rst | ||
| binfmt-misc.rst | ||
| bootconfig.rst | ||
| braille-console.rst | ||
| btmrvl.rst | ||
| bug-bisect.rst | ||
| bug-hunting.rst | ||
| cgroup-v2.rst | ||
| clearing-warn-once.rst | ||
| cpu-load.rst | ||
| cputopology.rst | ||
| dell_rbu.rst | ||
| devices.rst | ||
| devices.txt | ||
| dynamic-debug-howto.rst | ||
| edid.rst | ||
| efi-stub.rst | ||
| ext4.rst | ||
| highuid.rst | ||
| hw_random.rst | ||
| index.rst | ||
| init.rst | ||
| initrd.rst | ||
| iostats.rst | ||
| java.rst | ||
| jfs.rst | ||
| kernel-parameters.rst | ||
| kernel-parameters.txt | ||
| kernel-per-CPU-kthreads.rst | ||
| lcd-panel-cgram.rst | ||
| ldm.rst | ||
| lockup-watchdogs.rst | ||
| md.rst | ||
| module-signing.rst | ||
| mono.rst | ||
| numastat.rst | ||
| parport.rst | ||
| perf-security.rst | ||
| pnp.rst | ||
| pstore-blk.rst | ||
| ramoops.rst | ||
| rapidio.rst | ||
| ras.rst | ||
| README.rst | ||
| reporting-bugs.rst | ||
| rtc.rst | ||
| security-bugs.rst | ||
| serial-console.rst | ||
| spkguide.txt | ||
| svga.rst | ||
| sysfs-rules.rst | ||
| sysrq.rst | ||
| tainted-kernels.rst | ||
| thunderbolt.rst | ||
| ufs.rst | ||
| unicode.rst | ||
| vga-softcursor.rst | ||
| video-output.rst | ||
| xfs.rst | ||
.. _readme:
Linux kernel release 5.x <http://kernel.org/>
=============================================
These are the release notes for Linux version 5. Read them carefully,
as they tell you what this is all about, explain how to install the
kernel, and what to do if something goes wrong.
What is Linux?
--------------
Linux is a clone of the operating system Unix, written from scratch by
Linus Torvalds with assistance from a loosely-knit team of hackers across
the Net. It aims towards POSIX and Single UNIX Specification compliance.
It has all the features you would expect in a modern fully-fledged Unix,
including true multitasking, virtual memory, shared libraries, demand
loading, shared copy-on-write executables, proper memory management,
and multistack networking including IPv4 and IPv6.
It is distributed under the GNU General Public License v2 - see the
accompanying COPYING file for more details.
On what hardware does it run?
-----------------------------
Although originally developed first for 32-bit x86-based PCs (386 or higher),
today Linux also runs on (at least) the Compaq Alpha AXP, Sun SPARC and
UltraSPARC, Motorola 68000, PowerPC, PowerPC64, ARM, Hitachi SuperH, Cell,
IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64 Xtensa, and
ARC architectures.
Linux is easily portable to most general-purpose 32- or 64-bit architectures
as long as they have a paged memory management unit (PMMU) and a port of the
GNU C compiler (gcc) (part of The GNU Compiler Collection, GCC). Linux has
also been ported to a number of architectures without a PMMU, although
functionality is then obviously somewhat limited.
Linux has also been ported to itself. You can now run the kernel as a
userspace application - this is called UserMode Linux (UML).
Documentation
-------------
- There is a lot of documentation available both in electronic form on
the Internet and in books, both Linux-specific and pertaining to
general UNIX questions. I'd recommend looking into the documentation
subdirectories on any Linux FTP site for the LDP (Linux Documentation
Project) books. This README is not meant to be documentation on the
system: there are much better sources available.
- There are various README files in the Documentation/ subdirectory:
these typically contain kernel-specific installation notes for some
drivers for example. Please read the
:ref:`Documentation/process/changes.rst <changes>` file, as it
contains information about the problems, which may result by upgrading
your kernel.
Installing the kernel source
----------------------------
- If you install the full sources, put the kernel tarball in a
directory where you have permissions (e.g. your home directory) and
unpack it::
xz -cd linux-5.x.tar.xz | tar xvf -
Replace "X" with the version number of the latest kernel.
Do NOT use the /usr/src/linux area! This area has a (usually
incomplete) set of kernel headers that are used by the library header
files. They should match the library, and not get messed up by
whatever the kernel-du-jour happens to be.
- You can also upgrade between 5.x releases by patching. Patches are
distributed in the xz format. To install by patching, get all the
newer patch files, enter the top level directory of the kernel source
(linux-5.x) and execute::
xz -cd ../patch-5.x.xz | patch -p1
Replace "x" for all versions bigger than the version "x" of your current
source tree, **in_order**, and you should be ok. You may want to remove
the backup files (some-file-name~ or some-file-name.orig), and make sure
that there are no failed patches (some-file-name# or some-file-name.rej).
If there are, either you or I have made a mistake.
Unlike patches for the 5.x kernels, patches for the 5.x.y kernels
(also known as the -stable kernels) are not incremental but instead apply
directly to the base 5.x kernel. For example, if your base kernel is 5.0
and you want to apply the 5.0.3 patch, you must not first apply the 5.0.1
and 5.0.2 patches. Similarly, if you are running kernel version 5.0.2 and
want to jump to 5.0.3, you must first reverse the 5.0.2 patch (that is,
patch -R) **before** applying the 5.0.3 patch. You can read more on this in
:ref:`Documentation/process/applying-patches.rst <applying_patches>`.
Alternatively, the script patch-kernel can be used to automate this
process. It determines the current kernel version and applies any
patches found::
linux/scripts/patch-kernel linux
The first argument in the command above is the location of the
kernel source. Patches are applied from the current directory, but
an alternative directory can be specified as the second argument.
- Make sure you have no stale .o files and dependencies lying around::
cd linux
make mrproper
You should now have the sources correctly installed.
Software requirements
---------------------
Compiling and running the 5.x kernels requires up-to-date
versions of various software packages. Consult
:ref:`Documentation/process/changes.rst <changes>` for the minimum version numbers
required and how to get updates for these packages. Beware that using
excessively old versions of these packages can cause indirect
errors that are very difficult to track down, so don't assume that
you can just update packages when obvious problems arise during
build or operation.
Build directory for the kernel
------------------------------
When compiling the kernel, all output files will per default be
stored together with the kernel source code.
Using the option ``make O=output/dir`` allows you to specify an alternate
place for the output files (including .config).
Example::
kernel source code: /usr/src/linux-5.x
build directory: /home/name/build/kernel
To configure and build the kernel, use::
cd /usr/src/linux-5.x
make O=/home/name/build/kernel menuconfig
make O=/home/name/build/kernel
sudo make O=/home/name/build/kernel modules_install install
Please note: If the ``O=output/dir`` option is used, then it must be
used for all invocations of make.
Configuring the kernel
----------------------
Do not skip this step even if you are only upgrading one minor
version. New configuration options are added in each release, and
odd problems will turn up if the configuration files are not set up
as expected. If you want to carry your existing configuration to a
new version with minimal work, use ``make oldconfig``, which will
only ask you for the answers to new questions.
- Alternative configuration commands are::
"make config" Plain text interface.
"make menuconfig" Text based color menus, radiolists & dialogs.
"make nconfig" Enhanced text based color menus.
"make xconfig" Qt based configuration tool.
"make gconfig" GTK+ based configuration tool.
"make oldconfig" Default all questions based on the contents of
your existing ./.config file and asking about
new config symbols.
"make olddefconfig"
Like above, but sets new symbols to their default
values without prompting.
"make defconfig" Create a ./.config file by using the default
symbol values from either arch/$ARCH/defconfig
or arch/$ARCH/configs/${PLATFORM}_defconfig,
depending on the architecture.
"make ${PLATFORM}_defconfig"
Create a ./.config file by using the default
symbol values from
arch/$ARCH/configs/${PLATFORM}_defconfig.
Use "make help" to get a list of all available
platforms of your architecture.
"make allyesconfig"
Create a ./.config file by setting symbol
values to 'y' as much as possible.
"make allmodconfig"
Create a ./.config file by setting symbol
values to 'm' as much as possible.
"make allnoconfig" Create a ./.config file by setting symbol
values to 'n' as much as possible.
"make randconfig" Create a ./.config file by setting symbol
values to random values.
"make localmodconfig" Create a config based on current config and
loaded modules (lsmod). Disables any module
option that is not needed for the loaded modules.
To create a localmodconfig for another machine,
store the lsmod of that machine into a file
and pass it in as a LSMOD parameter.
Also, you can preserve modules in certain folders
or kconfig files by specifying their paths in
parameter LMC_KEEP.
target$ lsmod > /tmp/mylsmod
target$ scp /tmp/mylsmod host:/tmp
host$ make LSMOD=/tmp/mylsmod \
LMC_KEEP="drivers/usb:drivers/gpu:fs" \
localmodconfig
The above also works when cross compiling.
"make localyesconfig" Similar to localmodconfig, except it will convert
all module options to built in (=y) options. You can
also preserve modules by LMC_KEEP.
"make kvmconfig" Enable additional options for kvm guest kernel support.
"make xenconfig" Enable additional options for xen dom0 guest kernel
support.
"make tinyconfig" Configure the tiniest possible kernel.
You can find more information on using the Linux kernel config tools
in Documentation/kbuild/kconfig.rst.
- NOTES on ``make config``:
- Having unnecessary drivers will make the kernel bigger, and can
under some circumstances lead to problems: probing for a
nonexistent controller card may confuse your other controllers.
- A kernel with math-emulation compiled in will still use the
coprocessor if one is present: the math emulation will just
never get used in that case. The kernel will be slightly larger,
but will work on different machines regardless of whether they
have a math coprocessor or not.
- The "kernel hacking" configuration details usually result in a
bigger or slower kernel (or both), and can even make the kernel
less stable by configuring some routines to actively try to
break bad code to find kernel problems (kmalloc()). Thus you
should probably answer 'n' to the questions for "development",
"experimental", or "debugging" features.
Compiling the kernel
--------------------
- Make sure you have at least gcc 4.9 available.
For more information, refer to :ref:`Documentation/process/changes.rst <changes>`.
Please note that you can still run a.out user programs with this kernel.
- Do a ``make`` to create a compressed kernel image. It is also
possible to do ``make install`` if you have lilo installed to suit the
kernel makefiles, but you may want to check your particular lilo setup first.
To do the actual install, you have to be root, but none of the normal
build should require that. Don't take the name of root in vain.
- If you configured any of the parts of the kernel as ``modules``, you
will also have to do ``make modules_install``.
- Verbose kernel compile/build output:
Normally, the kernel build system runs in a fairly quiet mode (but not
totally silent). However, sometimes you or other kernel developers need
to see compile, link, or other commands exactly as they are executed.
For this, use "verbose" build mode. This is done by passing
``V=1`` to the ``make`` command, e.g.::
make V=1 all
To have the build system also tell the reason for the rebuild of each
target, use ``V=2``. The default is ``V=0``.
- Keep a backup kernel handy in case something goes wrong. This is
especially true for the development releases, since each new release
contains new code which has not been debugged. Make sure you keep a
backup of the modules corresponding to that kernel, as well. If you
are installing a new kernel with the same version number as your
working kernel, make a backup of your modules directory before you
do a ``make modules_install``.
Alternatively, before compiling, use the kernel config option
"LOCALVERSION" to append a unique suffix to the regular kernel version.
LOCALVERSION can be set in the "General Setup" menu.
- In order to boot your new kernel, you'll need to copy the kernel
image (e.g. .../linux/arch/x86/boot/bzImage after compilation)
to the place where your regular bootable kernel is found.
- Booting a kernel directly from a floppy without the assistance of a
bootloader such as LILO, is no longer supported.
If you boot Linux from the hard drive, chances are you use LILO, which
uses the kernel image as specified in the file /etc/lilo.conf. The
kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or
/boot/bzImage. To use the new kernel, save a copy of the old image
and copy the new image over the old one. Then, you MUST RERUN LILO
to update the loading map! If you don't, you won't be able to boot
the new kernel image.
Reinstalling LILO is usually a matter of running /sbin/lilo.
You may wish to edit /etc/lilo.conf to specify an entry for your
old kernel image (say, /vmlinux.old) in case the new one does not
work. See the LILO docs for more information.
After reinstalling LILO, you should be all set. Shutdown the system,
reboot, and enjoy!
If you ever need to change the default root device, video mode,
etc. in the kernel image, use your bootloader's boot options
where appropriate. No need to recompile the kernel to change
these parameters.
- Reboot with the new kernel and enjoy.
If something goes wrong
-----------------------
- If you have problems that seem to be due to kernel bugs, please check
the file MAINTAINERS to see if there is a particular person associated
with the part of the kernel that you are having trouble with. If there
isn't anyone listed there, then the second best thing is to mail
them to me (torvalds@linux-foundation.org), and possibly to any other
relevant mailing-list or to the newsgroup.
- In all bug-reports, *please* tell what kernel you are talking about,
how to duplicate the problem, and what your setup is (use your common
sense). If the problem is new, tell me so, and if the problem is
old, please try to tell me when you first noticed it.
- If the bug results in a message like::
unable to handle kernel paging request at address C0000010
Oops: 0002
EIP: 0010:XXXXXXXX
eax: xxxxxxxx ebx: xxxxxxxx ecx: xxxxxxxx edx: xxxxxxxx
esi: xxxxxxxx edi: xxxxxxxx ebp: xxxxxxxx
ds: xxxx es: xxxx fs: xxxx gs: xxxx
Pid: xx, process nr: xx
xx xx xx xx xx xx xx xx xx xx
or similar kernel debugging information on your screen or in your
system log, please duplicate it *exactly*. The dump may look
incomprehensible to you, but it does contain information that may
help debugging the problem. The text above the dump is also
important: it tells something about why the kernel dumped code (in
the above example, it's due to a bad kernel pointer). More information
on making sense of the dump is in Documentation/admin-guide/bug-hunting.rst
- If you compiled the kernel with CONFIG_KALLSYMS you can send the dump
as is, otherwise you will have to use the ``ksymoops`` program to make
sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred).
This utility can be downloaded from
https://www.kernel.org/pub/linux/utils/kernel/ksymoops/ .
Alternatively, you can do the dump lookup by hand:
- In debugging dumps like the above, it helps enormously if you can
look up what the EIP value means. The hex value as such doesn't help
me or anybody else very much: it will depend on your particular
kernel setup. What you should do is take the hex value from the EIP
line (ignore the ``0010:``), and look it up in the kernel namelist to
see which kernel function contains the offending address.
To find out the kernel function name, you'll need to find the system
binary associated with the kernel that exhibited the symptom. This is
the file 'linux/vmlinux'. To extract the namelist and match it against
the EIP from the kernel crash, do::
nm vmlinux | sort | less
This will give you a list of kernel addresses sorted in ascending
order, from which it is simple to find the function that contains the
offending address. Note that the address given by the kernel
debugging messages will not necessarily match exactly with the
function addresses (in fact, that is very unlikely), so you can't
just 'grep' the list: the list will, however, give you the starting
point of each kernel function, so by looking for the function that
has a starting address lower than the one you are searching for but
is followed by a function with a higher address you will find the one
you want. In fact, it may be a good idea to include a bit of
"context" in your problem report, giving a few lines around the
interesting one.
If you for some reason cannot do the above (you have a pre-compiled
kernel image or similar), telling me as much about your setup as
possible will help. Please read the :ref:`admin-guide/reporting-bugs.rst <reportingbugs>`
document for details.
- Alternatively, you can use gdb on a running kernel. (read-only; i.e. you
cannot change values or set break points.) To do this, first compile the
kernel with -g; edit arch/x86/Makefile appropriately, then do a ``make
clean``. You'll also need to enable CONFIG_PROC_FS (via ``make config``).
After you've rebooted with the new kernel, do ``gdb vmlinux /proc/kcore``.
You can now use all the usual gdb commands. The command to look up the
point where your system crashed is ``l *0xXXXXXXXX``. (Replace the XXXes
with the EIP value.)
gdb'ing a non-running kernel currently fails because ``gdb`` (wrongly)
disregards the starting offset for which the kernel is compiled.