Re: [Linux PPC] Disable PREEMPT

[Shrikanth Hegde <sshegde@linux.ibm.com>]

Hi Christian.


Is this sent as a patch or just a reply to the thread?

If it is sent as patch, Please follow these guidelines.
https://docs.kernel.org/process/submitting-patches.html

On 2/25/26 11:24 AM, Christian Zigotzky wrote:
> Hello,
> 
> We were previously able to disable PREEMPT in the kernel configuration, 
> but the latest kernels now enable it by default and it is no longer 
> possible to disable it.
> 
> Is it possible to let us decide whether to activate PREEMPT or not?
> 
> Currently we use the following revert patch for our non-preempt kernels.
> 
> --- a/kernel/Kconfig.preempt    2026-02-14 10:06:32.000000000 +0000
> +++ b/kernel/Kconfig.preempt    2026-02-08 21:03:27.000000000 +0000
> @@ -16,13 +16,11 @@ config ARCH_HAS_PREEMPT_LAZY
> 
>   choice
>       prompt "Preemption Model"
> -    default PREEMPT_LAZY if ARCH_HAS_PREEMPT_LAZY
>       default PREEMPT_NONE
> 
>   config PREEMPT_NONE
>       bool "No Forced Preemption (Server)"
>       depends on !PREEMPT_RT
> -    depends on ARCH_NO_PREEMPT
>       select PREEMPT_NONE_BUILD if !PREEMPT_DYNAMIC
>       help
>         This is the traditional Linux preemption model, geared towards
> @@ -37,7 +35,6 @@ config PREEMPT_NONE
> 
>   config PREEMPT_VOLUNTARY
>       bool "Voluntary Kernel Preemption (Desktop)"
> -    depends on !ARCH_HAS_PREEMPT_LAZY
>       depends on !ARCH_NO_PREEMPT
>       depends on !PREEMPT_RT
>       select PREEMPT_VOLUNTARY_BUILD if !PREEMPT_DYNAMIC
> 

I would instead fix any issue we have in PREEMPT FULL/LAZY rather than falling back to
old methods.

btw, did the previous patch sent, which you said helps you to boot, can you confirm
it did help you? If yes, i can send it as patch, since cond_resched if called from boot cpu
might be stuck in the loop forever.

IIRC, after boot, you had some driver causing crash. If so, share backtrace of the crash?
If you don't use that driver, is the guest stable?