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

[Frederic Weisbecker <frederic@kernel.org>]

Le Tue, Sep 22, 2026 at 07:53:23PM +0400, Ahmed Shaltout a écrit :
> Hi Frederic,
> 
> Le Mon, Sep 21, 2026, Frederic Weisbecker a écrit :
> > I can't manage to reproduce that, neither on latest mainline nor on 7.2.7
> >
> > Can you share your whole .config file?
> 
> Attached: config-7.2.5-1-default, taken from /boot/config-$(uname -r) on an
> affected node. It is the stock openSUSE Tumbleweed/MicroOS package
> kernel-default-7.2.5-1.1.x86_64, unmodified, no custom build. It differs
> from
> config/x86_64/default in openSUSE:Factory/kernel-source at the 7.2.5 source
> revision only in toolchain-detection and build-metadata lines (CC/AS/LD
> version, LOCALVERSION, MODULE_SIG_KEY, CC_HAS_*), no functional option:
> https://api.opensuse.org/public/source/openSUSE:Factory/kernel-source/config.tar.bz2?rev=4dabae0b715184e35b05b9a168bde6b7

I fear I still can't reproduce with the config in attachment.

> 
> The unaffected control box runs kernel-default-7.1.8-1.1.x86_64 from the
> same
> distribution, also stock, same VM type, same command line. Between the two
> configs the only change among the scheduler, tick, accounting, preemption
> and
> RCU options is CONFIG_SCHED_CACHE=y appearing in 7.2.5.
> 
> Environment, in case it is what your test box does not share:
> 
>   - Every node is a KVM guest (Hetzner Cloud, QEMU, "AMD EPYC-Rome
> Processor",
>     8 vCPUs, one with 4), clocksource kvm-clock.
>   - No steal-time accounting at all: there is no kvm-stealtime line in the
>     boot log and the steal column has read exactly 0 on every node for the
>     75 hours since boot, so the hypervisor does not seem to expose the MSR.
>   - CONFIG_VIRT_CPU_ACCOUNTING_GEN=y, CONFIG_CONTEXT_TRACKING_IDLE=y and
>     CONFIG_NO_HZ_FULL=y are built in (SUSE default) with nohz_full= empty,
>     so the CPUs run idle dynticks, not full.
>   - CONFIG_HZ=1000, CONFIG_PREEMPT_DYNAMIC=y, psi=1 on the command line:
>     BOOT_IMAGE=/boot/vmlinuz-7.2.5-1-default root=UUID=... rd.timeout=60
>     rd.retry=45 quiet systemd.show_status=yes console=ttyS0,115200
>     console=tty0 ignition.platform.id=openstack security=selinux selinux=1
>     psi=1

I ran on KVM too, overcommiting the vcpus like you did (16 vCPUs on 8 CPUs)
and still nothing wrong.

I'm wondering if this is specific to opensuse somehow. Can you try to build
the latest upstream kernel?

Thanks.

-- 
Frederic Weisbecker
SUSE Labs