can the idle value of /proc/stat decrease?

can the idle value of /proc/stat decrease?

[xuqiang (M)]

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

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@huawei.com> 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@cloud.ionos.com | Web: www.ionos.de

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