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Thu, 26 Feb 2026 13:24:54 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5D220C116C6; Thu, 26 Feb 2026 13:24:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772112294; bh=2/QPW79kVlJl5CXnRPzQ9jK+/xV64cz0chwvlkpUCTY=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ZzRWg6m3RkIiQsJnc5Rn30PQvsl3rrrmyfR917f2UY7UE2nwVO3siznjTO/0Yw5J4 Sed00gijglV/Z8/jXNTglE+v102BhOFpTrHJg1fDqU8rMl17AnlBdAEXRllRx3ARmQ SHkp5RpkIfK/t9004lI3/tjAq/2V20Itfsl4afyGVcOD9pTR0Du9eOM182lHXJdqPE zENeXInjUc0gRjvF+njZ8zD4K5TcY/Rw8n4tgdhyKbx4fZ3qOAeOL9WO0c0wkLvrSh ZfS3mJnDCPCTaP/3c5knJOl5zz/7+tSUXZ+amLqCXYg+M4S46GgBnrYweFDMEtPmpg T4qtzqNx+vZfg== Message-ID: <8c6f2510-1dc5-4c45-9288-6b9c8f9b6b24@kernel.org> Date: Thu, 26 Feb 2026 14:24:50 +0100 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [Linux PPC] Disable PREEMPT To: Christian Zigotzky , Shrikanth Hegde , linuxppc-dev , "kvm-ppc@vger.kernel.org" , Madhavan Srinivasan , Peter Zijlstra Cc: "R.T.Dickinson" , hypexed@yahoo.com.au, mad skateman , Christian Zigotzky References: <185d7a42-f7b4-44e1-a129-f5989d211c74@linux.ibm.com> <40154f6a-39da-959d-e039-5ab9ff62db3c@xenosoft.de> <709b864f-9daa-4a48-b3d6-39baedce63b2@linux.ibm.com> <843b7c60-23f1-47d0-b4e8-2147c3e40c23@linux.ibm.com> <2a27e6fc-7eb4-41a5-ba88-58f6a22625b5@xenosoft.de> <1d79ec6f-ce7f-4432-80e0-a54fa1668642@linux.ibm.com> <1c9b879a-7907-4849-a416-5df3db5617d6@kernel.org> <34112e67-85a5-a380-a42b-24c6562d65be@xenosoft.de> Content-Language: fr-FR From: "Christophe Leroy (CS GROUP)" In-Reply-To: <34112e67-85a5-a380-a42b-24c6562d65be@xenosoft.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 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 >>> >> > >