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

[No SPAM here]

Thanks Chaoyi, Hello Peter.

I have run `openssl speed -multi 8 rsa md5 sha256 sha512 aes sha1  camellia  des rmd160` while booted to the same 6.18.52 kernel, one built with CONFIG_SCHED_CLUSTER=y and one with it =n. This produces a lot of output and runs for about 8.5 minutes and puts out a 21 line table of statistics. I've compared a fair few of the numbers from both runs and most of the numbers from the cluster=n run are between 8 and 11% higher which seems to back up the idea that it's just not using one whole core of the 8 available. I've attached the two 21 line summaries here, CLUSTER=n results are in openssl-speed-nocluster.txt and CLUSTER=y in openssl-speed-cluster.txt.

Trevor

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
> 
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