Re: [REGRESSION] /proc/stat idle time exceeds wall clock since v7.2

[Frederic Weisbecker]

Hi Ahmed,

Le Sun, Sep 20, 2026 at 03:14:22AM +0400, Ahmed Shaltout a écrit :
> Hello,
> 
> Since moving from 7.1.8 to 7.2.5 (openSUSE MicroOS kernel-default), the idle
> time reported in /proc/stat exceeds the wall-clock time the CPUs have been up
> for. Idle alone accrues ~103% of the ceiling, and user+nice+system+idle+iowait
> +irq+softirq+steal sums to ~108% of it.
> 
> This breaks the common `100 - rate(idle)` derivation of CPU utilisation, which
> goes negative on an idle-but-working machine. node_exporter, and anything built
> on it, is affected.
> 
> #regzbot introduced: v7.1..v7.2
> 
> Reproducer
> ==========
> 
> No tooling needed; /proc/uptime shows it directly, since its second field is
> idle time and cannot legitimately exceed uptime x nr_cpus:
> 
>   read -r up idle < /proc/uptime && awk -v u="$up" -v i="$idle" -v c="$(nproc)" \
>     'BEGIN{printf "idle %.2f%% of ceiling\n", 100*i/(u*c)}'
> 
>   7.2.5:  idle 103.10% of ceiling
>   7.1.8:  idle  89.13% of ceiling

I can't manage to reproduce that, neither on latest mainline nor on 7.2.7

Can you share your whole .config file?

Thanks.

-- 
Frederic Weisbecker
SUSE Labs