[BUG?] Possible scheduler bug on Rock 5B RK3588 on 7.2.5

[No SPAM here]

I have now retested with kernel 7.3.0-rc3 and this bug appears to have been fixed. The same command now runs all 8 cores at 100% for the duration of the test and the resulting numbers differ (in favour of the 6.18.52 CLUSTER=n kernel) by a maximum of 0.25% which is measurement error.

Thanks for your attention. This can be marked as solved.

Trevor


Sent with Proton Mail secure email.

On Friday, 18 September 2026 at 02:22, Chaoyi Chen <chaoyi.chen at rock-chips.com> wrote:

> On 9/18/2026 3:15 AM, No SPAM here wrote:
> > Hi
> >
> > On Thursday, 17 September 2026 at 03:37, Chaoyi Chen <chaoyi.chen at rock-chips.com> wrote:
> >
> >> Hello Trevor,
> >>
> >> On 9/17/2026 9:21 AM, No SPAM here wrote:
> >>>> Would you mind trying to disable `CONFIG_SCHED_CLUSTER` and checking whether
> >>>> the problem still reproduces?
> >
> > trevor at rock-5b:~$ uname -a
> > Linux rock-5b 6.18.52-current-rockchip64 #1 SMP PREEMPT Mon Sep 14 11:36:19 UTC 2026 aarch64 GNU/Linux
> > trevor at rock-5b:~$ grep CONFIG_SCHED_CLU /boot/config-6.18.52-current-rockchip64
> > # CONFIG_SCHED_CLUSTER is not set
> > trevor at rock-5b:~$ sar | tail -5
> >
> > 18:50:15        CPU     %user     %nice   %system   %iowait    %steal     %idle
> > 19:00:15        all     99.89      0.00      0.11      0.00      0.00      0.00
> > 19:10:15        all     99.89      0.00      0.11      0.00      0.00      0.00
> > Average:        all     99.89      0.00      0.11      0.00      0.00      0.00
> >
> > Been running stress --cpu 8 since 18:47 and so far it is using all 8 cores at 100%. It would normally have shown the 7/8ths problem after 20s or so, maybe 2 or 3 minutes at max. So I'd say this setting is definitely involved.
> >
> 
> Thank you very much for testing. I'm not a scheduler expert, but I see
> that CONFIG_SCHED_CLUSTER is enabled by default on arm64 [0].
> 
> Peter is the maintainer and author of this series.
> @Peter, do you have any further insights? Thank you!
> 
> This thread background is here[1].
> 
> [0]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7bd291abe2da09f59dca81f35a4ec220e5e138a2
> [1]: https://lore.kernel.org/all/f15f8166-c1e4-45dc-9ddd-4ec887e415eb@gdead.co.uk/
> 
> --
> Best,
> Chaoyi
>