CONFIG_LOG_BUF_SHIFT is too low on arm64

[Dimitri John Ledkov]

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.

Please backport this to xenial and up.

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1824863

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.