** Changed in: linux (Ubuntu Disco)
Status: Confirmed => Fix Committed
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https://bugs.launchpad.net/bugs/1824864
Title:
CONFIG_LOG_BUF_SHIFT set to 14 is too low on arm64
Status in linux package in Ubuntu:
Confirmed
Status in systemd package in Ubuntu:
New
Status in linux source package in Xenial:
Confirmed
Status in systemd source package in Xenial:
New
Status in linux source package in Bionic:
Confirmed
Status in systemd source package in Bionic:
New
Status in linux source package in Cosmic:
Confirmed
Status in systemd source package in Cosmic:
New
Status in linux source package in Disco:
Fix Committed
Status in systemd source package in Disco:
New
Status in linux source package in Eoan:
Confirmed
Status in systemd source package in Eoan:
New
Bug description:
[Impact]
* Too small dmsg kernel buf ring size leads to loosing/missing early
boot kernel messages which happen before journald starts slurping them
up and storing them on disc. This results in messages similar to this
one on boot "missed NN kernel messages on boot". This is especially
pronounced on arm64 as the default setting there is way lower than any
other 32bit or 64bit architecture we ship. Also amd64 appears to have
the highest setting of 18 among all architectures we ship. The best
course of action to bump all 64bit arches to 18, and keep all 32bit
arches at the current & upstream default of 17.
[Test Case]
* $ cat /boot/config-`uname -r` | grep CONFIG_LOG_BUF_SHIFT
on 64bit arches result should be: CONFIG_LOG_BUF_SHIFT=18
on 32bit arches result should be: CONFIG_LOG_BUF_SHIFT=17
* run systemd adt test, the boot-and-services test case should not
fail journald tests with "missed kernel messages" visible in the error
logs.
[Regression Potential]
* Increasing the size of the log_buf, will increase kernel memory
usage which cannot be reclaimed. It will now become 256kb on arm64,
ppc64el, s390x instead of 8kB/128kb/128kb respectively. 32bit arches
remain unchanged at 128kb.
[Other Info]
* Original bug report
CONFIG_LOG_BUF_SHIFT
policy<{
'amd64' : '18',
'arm64' : '14',
'armhf' : '17',
'i386' : '17',
'ppc64el': '17',
's390x' : '17'}>
Please set CONFIG_LOG_BUF_SHIFT to at least 17 on arm64.
Potentially bump all 64-bit arches to 18 (or higher!) as was done on
amd64, meaning set 18 on arm64 s390x ppc64el.
I have a systemd autopkgtest test that asserts that we see Linux
kernel command line in the dmesg (journalctl -k -b). And it is
consistently failing on arm64 scalingstack KVM EFI machines with
messages of "missing 81 kernel messages".
config LOG_BUF_SHIFT
int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
range 12 25
default 17
depends on PRINTK
help
Select the minimal kernel log buffer size as a power of 2.
The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
parameter, see below. Any higher size also might be forced
by "log_buf_len" boot parameter.
Examples:
17 => 128 KB
16 => 64 KB
15 => 32 KB
14 => 16 KB
13 => 8 KB
12 => 4 KB
14 sounds like redictiously low for arm64. given that 17 is default
across 32-bit arches, and 18 is default on amd64.
On a related note, we have CONFIG_PRINTK_SAFE_LOG_BUF_SHIFT
policy<{'amd64': '13', 'arm64': '13', 'armhf': '13', 'i386': '13', 'ppc64el':
'13', 's390x': '13'}>
I'm not sure if we want to bump these up to LOG_BUF_SHIFT size or not.
Please backport this to xenial and up.
=== systemd ===
systemd, boot-and-services test case can bump the ring buffer before
running the tests.
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