Re: [Linux PPC] Disable PREEMPT

["Christophe Leroy (CS GROUP)" <chleroy@kernel.org>]

Hi Christian,

Le 26/02/2026 à 06:37, Christian Zigotzky a écrit :
> On 25/02/26 08:16, Christophe Leroy (CS GROUP) wrote:
>> +Peter
>>
>> Hi Christian,
>>
>> Le 25/02/2026 à 06:54, Christian Zigotzky a écrit :
>>> 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?
>>
>> Can you give more details on why you want to be able to deactivate 
>> PREEMPT ?
>>
>> Read https://eur01.safelinks.protection.outlook.com/? 
>> url=https%3A%2F%2Fgithub.com%2Ftorvalds%2Flinux%2Fcommit%2F7dadeaa6e851e&data=05%7C02%7Cchristophe.leroy2%40cs-soprasteria.com%7C7006c8b4b98c4315a7e508de74f9388a%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639076810956939768%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=6xLB%2FOVSkmgZRamaBM9zaxm%2FUTk9ssf4409QJdiXkDg%3D&reserved=0
> I use PREEMPT_NONE kernels on my Linux PPC servers. (Without desktop)

You are doing that today because it is possible. Tomorrow it will not be 
possible anymore, for the reasons explained by Peter.

My question was not to know what you are doing but why, and why you 
think you still need PREEMPT_NONE and why the modern PREEMPT_LAZY is not 
good enough for you.

Christophe

>>
>>
>>>
>>> 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
>>>
>>> ---
>>>
>>> Thanks in advance,
>>>
>>> Christian
>>>
>>
> 
>