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

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Date:   Wed, 20 Sep 2023 10:37:42 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Linus Torvalds' <torvalds@...ux-foundation.org>,
        "John Paul Adrian Glaubitz" <glaubitz@...sik.fu-berlin.de>
CC:     Peter Zijlstra <peterz@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ankur Arora <ankur.a.arora@...cle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "luto@...nel.org" <luto@...nel.org>, "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "juri.lelli@...hat.com" <juri.lelli@...hat.com>,
        "vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
        "mgorman@...e.de" <mgorman@...e.de>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "jon.grimm@....com" <jon.grimm@....com>,
        "bharata@....com" <bharata@....com>,
        "raghavendra.kt@....com" <raghavendra.kt@....com>,
        "boris.ostrovsky@...cle.com" <boris.ostrovsky@...cle.com>,
        "konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
        "jgross@...e.com" <jgross@...e.com>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "linux-m68k@...ts.linux-m68k.org" <linux-m68k@...ts.linux-m68k.org>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>,
        "linux-um@...ts.infradead.org" <linux-um@...ts.infradead.org>,
        Brian Cain <bcain@...cinc.com>,
        "linux-hexagon@...r.kernel.org" <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" <linux-alpha@...r.kernel.org>
Subject: RE: Arches that don't support PREEMPT

From: Linus Torvalds
> Sent: 19 September 2023 18:25
> 
> On Tue, 19 Sept 2023 at 06:48, John Paul Adrian Glaubitz
> <glaubitz@...sik.fu-berlin.de> wrote:
> >
> > As Geert poined out, I'm not seeing anything particular problematic with the
> > architectures lacking CONFIG_PREEMPT at the moment. This seems to be more
> > something about organizing KConfig files.
> 
> It can definitely be problematic.
> 
> Not the Kconfig file part, and not the preempt count part itself.
> 
> But the fact that it has never been used and tested means that there
> might be tons of "this architecture code knows it's not preemptible,
> because this architecture doesn't support preemption".

Do distos even build x86 kernels with PREEMPT_FULL?
I know I've had issues with massive latencies caused graphics driver
forcing write-backs of all the framebuffer memory.
(I think it is a failed attempt to fix a temporary display corruption.)

OTOH SMP support and CONFIG_RT will test most of the code.

	David

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