linux-kernel - Re: [PATCH 0/3] Allow to enable PREEMPT

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Message-ID: <20240930102223.j780j0oy@linutronix.de>
Date: Mon, 30 Sep 2024 12:22:23 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	John Ogness <john.ogness@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH 0/3] Allow to enable PREEMPT_RT.

On 2024-09-30 10:39:17 [+0530], Shrikanth Hegde wrote:
> Hi Sebastian.
Hi Shrikanth,

> 
> Added the ARCH_SUPPORTS_RT in arch/powerpc/Kconfig. Selected the preempt_rt in menuconfig.
> It *compiled and booted successfully* on POWERPC/ppc64le.

…
> So, Curious to know what are those patches that are left for POWERPC?
> would like to work on those and get it enabled on POWERPC.

Based on [0] this is what I have in my queue:
| powerpc__traps__Use_PREEMPT_RT.patch
| powerpc_pseries_iommu__Use_a_locallock_instead_local_irq_save.patch
| powerpc-pseries-Select-the-generic-memory-allocator.patch
| powerpc_kvm__Disable_in-kernel_MPIC_emulation_for_PREEMPT_RT.patch
| powerpc_stackprotector__work_around_stack-guard_init_from_atomic.patch
| POWERPC__Allow_to_enable_RT.patch

Be aware that PREEMPT_RT run only on 32bit PowerPC and 64bit from FSL
which is the embedded variant. That means it (64bit) had altivec but
also a "simple" MMU. The P-Series (server grade hardware) version has a
hashing MMU which has additional locking constrains. I never tested this
outside of qemu and this was limited to booting.

The traps patch in the queue was submitted a while ago
	https://lore.kernel.org/linuxppc-dev/20191015191821.11479-4-bigeasy@linutronix.de/

and reduced to the traps.c part.
The powerpc should be reviewed and then decided what to do with them
before enabling.

[0] https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/tree/patches/series?h=v6.11-rt7-patches&id=28e79a9ab2504e245837070f27f525520a6f5acb#n147

Sebastian