[systemd-devel] What causes "systemd-journald[3256]: Missed 127 kernel messages"

[Ulrich Windl]

Hi!

Debugging an issue (a few hundred processes hanging)  I used "echo w >/proc/sysrq-trigger". When viewing the journal I found out that it's incomplete, saying (grep Missed):
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 3990 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 252 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 117 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 127 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 123 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 126 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 122 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 123 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 252 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 122 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 124 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 122 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 373 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 125 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 122 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 123 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 125 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 126 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 127 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 123 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 122 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 127 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 122 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 123 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 121 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 255 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 122 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 122 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 124 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 250 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 124 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 122 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 125 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 123 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 122 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 121 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 123 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 122 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 123 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 125 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 128 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 128 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 128 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 124 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 132 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 128 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 128 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 257 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 128 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 128 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 253 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 132 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 128 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 128 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 128 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 128 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 128 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 128 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 128 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 128 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 128 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 135 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 139 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 138 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 134 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 139 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 413 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 134 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 138 kernel messages
Jun 01 12:33:10 h18 systemd-journald[3256]: Missed 195 kernel messages

A few questions:
1) What causes this?
2) How can systemd know how many messasges were missed?
3) Can I avoid that problem?

(systemd-234-24.82.1.x86_64 of SLES 15 SP2)

Regards,
Ulrich