Re: can the idle value of /proc/stat decrease?

[Gioh Kim]

Hi,

We found the same problem on our production servers.

For example, prometheus-node-exporter reported below message:
daemon.info: Feb  8 17:43:12 ps601b-202
prometheus-node-exporter[2506]: level=warn ts=2021-02-08T17:43:12.052Z
caller=cpu_linux.go:247 collector=cpu msg="CPU Idle counter jumped
backwards, possible hotplug event, resetting CPU stats" cpu=78
old_value=1.04782328e+06 new_value=1.04782178e+06

The idle value was changed from 1.04782328e+06 to 1.04782178e+06.

AND the server rebooted after some minutes.
There is no other error in the log files.
I currently suspect the CPU counter decreasing caused the system reboot.

On Mon, Dec 28, 2020 at 8:57 AM xuqiang (M) <xuqiang36@xxxxxxxxxx> wrote:
>
> Our recent test shows that the idle value of /proc/stat can decrease.
> Is this an unreported bug? or it has been reported and the solution is
> waiting to get merged.
>
> The results of the two readings from /proc/stat are shown as below, the
> interval between the two readings is 150 ms:
>
> cat /proc/stat
> cpu0 5536 10 14160 4118960 0 0 227128 0 0 0
>
> cat /proc/stat
> cpu0 5536 10 14160 4118959 0 0 227143 0 0 0



-- 
Gioh Kim

Cloud server kernel maintainer
Quality Management (IONOS Cloud)

1&1 IONOS SE | Greifswalder Str. 207 | 10405 Berlin | Germany
Phone: +49 176 26978962
E-mail: gi-oh.kim@xxxxxxxxxxxxxxx | Web: www.ionos.de

Hauptsitz Montabaur, Amtsgericht Montabaur, HRB 24498

Vorstand: Dr. Christian Böing, Hüseyin Dogan, Dr. Martin Endreß,
Hans-Henning Kettler, Arthur Mai, Matthias Steinberg, Achim Weiß
Aufsichtsratsvorsitzender: Markus Kadelke

Member of United Internet

Diese E-Mail kann vertrauliche und/oder gesetzlich geschützte
Informationen enthalten. Wenn Sie nicht der bestimmungsgemäße Adressat
sind oder diese E-Mail irrtümlich erhalten haben, unterrichten Sie
bitte den Absender und vernichten Sie diese E-Mail. Anderen als dem
bestimmungsgemäßen Adressaten ist untersagt, diese E-Mail zu
speichern, weiterzuleiten oder ihren Inhalt auf welche Weise auch
immer zu verwenden.

This e-mail may contain confidential and/or privileged information. If
you are not the intended recipient of this e-mail, you are hereby
notified that saving, distribution or use of the content of this
e-mail in any way is prohibited. If you have received this e-mail in
error, please notify the sender and delete the e-mail.