linux-kernel - RE: [PATCH] powerpc: Allow scheduling of IRQ with PREEMPT

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Message-ID:
 <SJ2PR22MB3822B4550212A2418187A075E5112@SJ2PR22MB3822.namprd22.prod.outlook.com>
Date: Tue, 7 Jan 2025 18:13:07 +0000
From: Robert Joslyn <robert_joslyn@...inc.com>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "rostedt@...dmis.org"
	<rostedt@...dmis.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: RE: [PATCH] powerpc: Allow scheduling of IRQ with PREEMPT_RT

> -----Original Message-----
> From: Shrikanth Hegde <sshegde@...ux.ibm.com>
> Sent: Tuesday, January 7, 2025 5:10 AM
> To: Robert Joslyn <robert_joslyn@...inc.com>
> Cc: linux-kernel@...r.kernel.org; linux-rt-users@...r.kernel.org;
> tglx@...utronix.de; rostedt@...dmis.org; Sebastian Andrzej Siewior
> <bigeasy@...utronix.de>
> Subject: Re: [PATCH] powerpc: Allow scheduling of IRQ with PREEMPT_RT
> 
> [Caution - External]
> 
> On 1/7/25 17:26, Sebastian Andrzej Siewior wrote:
> > On 2024-12-26 11:12:38 [-0800], Robert Joslyn wrote:
> >> This branch is needed to allow preemptible IRQs to be scheduled,
> >> otherwise the kernel hangs during boot on my e300 based platforms.
> >> This branch is needed for both CONFIG_PREEMPT and
> CONFIG_PREEMPT_RT,
> 
> Hi Robert.
> 
> Are you running with preempt=full or enabled preempt_rt ?
> rt is yet to be supported on powerpc. are you having it enabled out of tree?

I'm running PREEMPT_RT using the out of tree patches on 6.6.58-rt45:
https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-stable-rt.git/

I haven't tried using the mainline kernel, since as you said, it doesn't have powerpc support for PREEMPT_RT yet.

> 
> Also, I have sent out patch to enable dynamic preemption. It uses
> preempt_model_preemptible.
> I think it should work for you as well. If you could give that a try and ensure it
> works, it would be great.
> https://urldefense.com/v3/__https://lore.kernel.org/all/20250106051919.5
> 5020-2-
> sshegde@...ux.ibm.com/__;!!O7uE89YCNVw!IDeomstGeuiEZi9FmLHH8C2xo
> PPo_ewL-
> k2kiQ9CmVID35U4J_v3Dkafjo3RnS9ygPoUZWwyyp91SP2euRkKArk$

Does the dynamic preemption support let me enable the same functionality as PREEMPT_RT with the out of tree patches? I can test it out either way.

Thanks,
Robert