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

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Message-ID: <e0364c9a-0364-4993-99a1-9e51a47529fe@linux.ibm.com>
Date: Wed, 8 Jan 2025 10:26:36 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: Robert Joslyn <robert_joslyn@...inc.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



On 1/7/25 23:43, Robert Joslyn wrote:
>> -----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.
> 


with preempt_rt, dynamic preemption allows you to switch between full 
and lazy. without preempt_rt, you can switch between none, 
voluntary,full and lazy.


> Thanks,
> Robert