linux-kernel - Re: Arches that don't support PREEMPT

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Message-ID: <9a5c0856-d542-9912-7494-53d7fe4538a3@cambridgegreys.com>
Date:   Tue, 19 Sep 2023 16:21:29 +0100
From:   Anton Ivanov <anton.ivanov@...bridgegreys.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ankur Arora <ankur.a.arora@...cle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
        akpm@...ux-foundation.org, luto@...nel.org, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, mingo@...hat.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org, mgorman@...e.de,
        rostedt@...dmis.org, jon.grimm@....com, bharata@....com,
        raghavendra.kt@....com, boris.ostrovsky@...cle.com,
        konrad.wilk@...cle.com, jgross@...e.com, andrew.cooper3@...rix.com,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-m68k@...ts.linux-m68k.org,
        Richard Weinberger <richard@....at>,
        Johannes Berg <johannes@...solutions.net>,
        linux-um@...ts.infradead.org, Brian Cain <bcain@...cinc.com>,
        linux-hexagon@...r.kernel.org,
        Richard Henderson <richard.henderson@...aro.org>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>, linux-alpha@...r.kernel.org
Subject: Re: Arches that don't support PREEMPT


On 19/09/2023 16:17, Thomas Gleixner wrote:
> On Tue, Sep 19 2023 at 15:21, Anton Ivanov wrote:
>> On 19/09/2023 14:42, Peter Zijlstra wrote:
>>> If you're working on one of them, then surely it's a simple matter of
>>> working on adding CONFIG_PREEMPT support :-)
>> In the case of UML adding preempt will be quite difficult. I looked at
>> this a few years back.
> What's so difficult about it?

It's been a while. I remember that I dropped it at the time, but do not remember the full details.

There was some stuff related to FP state and a few other issues I ran into while rewriting the interrupt controller. Some of it may be resolved by now as we are using host cpu flags, etc.

I can give it another go :)

>
> Thanks,
>
>          tglx
>
-- 
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661
https://www.cambridgegreys.com/