From: Peter Zijlstra <peterz@infradead.org>
To: "Christophe Leroy (CS GROUP)" <chleroy@kernel.org>
Cc: Christian Zigotzky <chzigotzky@xenosoft.de>,
Shrikanth Hegde <sshegde@linux.ibm.com>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
"kvm-ppc@vger.kernel.org" <kvm-ppc@vger.kernel.org>,
Madhavan Srinivasan <maddy@linux.ibm.com>,
"R.T.Dickinson" <rtd2@xtra.co.nz>,
hypexed@yahoo.com.au, mad skateman <madskateman@gmail.com>,
Christian Zigotzky <info@xenosoft.de>
Subject: Re: [Linux PPC] Disable PREEMPT
Date: Wed, 25 Feb 2026 12:36:53 +0100 [thread overview]
Message-ID: <20260225113653.GM3016024@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <1c9b879a-7907-4849-a416-5df3db5617d6@kernel.org>
On Wed, Feb 25, 2026 at 08:16:46AM +0100, 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://github.com/torvalds/linux/commit/7dadeaa6e851e
Right. So to recap, there are and will be more cases where relying on
preemption is mandatory.
The typical example is huge page memset/memcpy. Currently that is done
in single page chunks with cond_resched() in between, but it is much
better (and faster) to do a full huge page in one go.
Combine this with the endless stream of mostly random cond_resched()
placements due to $reason, and it is all a bit of a maintenance
nightmare.
I suppose the question is; why do you think you require non-preempt
kernels?
next prev parent reply other threads:[~2026-02-25 11:36 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-14 14:02 [Linux PPC] KVM PR and KVM HV do not work if the kernel was compiled with PREEMPT Christian Zigotzky
2026-02-17 5:02 ` Shrikanth Hegde
2026-02-17 8:52 ` Christian Zigotzky
2026-02-17 9:03 ` Shrikanth Hegde
2026-02-17 9:44 ` Christian Zigotzky
2026-02-17 10:17 ` Madhavan Srinivasan
2026-02-17 10:26 ` Christian Zigotzky
2026-02-17 11:34 ` Shrikanth Hegde
2026-02-21 5:30 ` Christian Zigotzky
2026-02-23 3:45 ` Shrikanth Hegde
2026-02-23 16:48 ` [Linux PPC] 7.0-rc1: e500_mmu.c:923:26: error: assignment to 'struct tlbe_priv *' from incompatible pointer type 'struct tlbe_ref *' Christian Zigotzky
2026-02-23 18:07 ` Christophe Leroy (CS GROUP)
2026-02-23 19:38 ` Christophe Leroy (CS GROUP)
2026-02-23 22:40 ` Kees Cook
2026-02-24 6:30 ` Christian Zigotzky
2026-02-24 7:18 ` Christophe Leroy (CS GROUP)
2026-02-25 5:54 ` [Linux PPC] Disable PREEMPT Christian Zigotzky
2026-02-25 6:23 ` Shrikanth Hegde
2026-02-25 7:16 ` Christophe Leroy (CS GROUP)
2026-02-25 11:36 ` Peter Zijlstra [this message]
2026-02-26 5:37 ` Christian Zigotzky
2026-02-26 13:24 ` Christophe Leroy (CS GROUP)
2026-09-03 9:53 ` Michal Suchánek
2026-09-03 10:56 ` Shrikanth Hegde
2026-09-03 11:25 ` Michal Suchánek
2026-09-03 11:31 ` Shrikanth Hegde
2026-09-03 11:40 ` Michal Suchánek
2026-09-03 12:04 ` Shrikanth Hegde
2026-09-03 12:25 ` Michal Suchánek
2026-09-03 12:36 ` Harsh Prateek Bora
2026-09-03 12:55 ` Michal Suchánek
2026-09-03 15:17 ` Amit Machhiwal
2026-09-03 13:28 ` Michal Suchánek
2026-09-04 7:39 ` Michal Suchánek
2026-09-03 17:22 ` Shrikanth Hegde
2026-09-04 7:35 ` Michal Suchánek
2026-09-04 9:04 ` Shrikanth Hegde
2026-09-10 8:59 ` Michal Suchánek
2026-09-10 10:41 ` Shrikanth Hegde
2026-09-10 11:29 ` Michal Suchánek
2026-09-10 12:16 ` Michal Suchánek
2026-09-11 17:09 ` Shrikanth Hegde
2026-09-04 8:55 ` Christian Zigotzky
2026-09-04 9:20 ` Christian Zigotzky
2026-09-04 9:24 ` Shrikanth Hegde
2026-09-04 9:34 ` Christian Zigotzky
2026-09-05 13:07 ` Christian Zigotzky
2026-09-07 8:50 ` Michal Suchánek
2026-09-07 11:32 ` Christian Zigotzky
2026-09-10 8:54 ` Michal Suchánek
2026-09-10 10:31 ` Michal Suchánek
2026-09-10 11:31 ` Michal Suchánek
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