linux-kernel - Re: ppc64le: `NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #20!!!` when turning off SMT

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Date:   Tue, 8 Feb 2022 08:35:35 +0100
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Frederic Weisbecker <fweisbec@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, linuxppc-dev@...ts.ozlabs.org
Subject: Re: ppc64le: `NOHZ tick-stop error: Non-RCU local softirq work is
 pending, handler #20!!!` when turning off SMT

[attach output of `dmesg`]

Am 08.02.22 um 08:32 schrieb Paul Menzel:
> Dear Linux folks,
> 
> 
> On the POWER8 server IBM S822LC running Ubuntu 21.10, Linux 5.17-rc1+ 
> built with
> 
>      $ grep HZ /boot/config-5.17.0-rc1+
>      CONFIG_NO_HZ_COMMON=y
>      # CONFIG_HZ_PERIODIC is not set
>      CONFIG_NO_HZ_IDLE=y
>      # CONFIG_NO_HZ_FULL is not set
>      CONFIG_NO_HZ=y
>      # CONFIG_HZ_100 is not set
>      CONFIG_HZ_250=y
>      # CONFIG_HZ_300 is not set
>      # CONFIG_HZ_1000 is not set
>      CONFIG_HZ=250
> 
> once warned about a NOHZ tick-stop error, when I executed `sudo 
> /usr/sbin/ppc64_cpu --smt=off` (so that KVM would work).
> 
> ```
> $ dmesg
> [    0.000000] Linux version 5.17.0-rc1+ 
> (pmenzel@...ghafenberlinbrandenburgwillybrandt.molgen.mpg.de) (Ubuntu clang version 13.0.0-2, LLD 13.0.0) #1 SMP Fri Jan 28 17:13:04 CET 2022
> […]
> [271272.030262] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #20!!!
> [271272.305726] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #20!!!
> [271272.549790] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #20!!!
> [271274.885167] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #20!!!
> [271275.113896] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #20!!!
> [271275.412902] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #20!!!
> [271275.625245] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #20!!!
> [271275.833107] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #20!!!
> [271276.041391] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #20!!!
> [271277.244880] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #20!!!
> ```
> 
> 
> Kind regards,
> 
> Paul
View attachment "linux-5.17-rc1+-nohz-tick-stop-error.txt" of type "text/plain" (180962 bytes)