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Message-ID: <ZQqgFpA6l1eK1KKV@gmail.com>
Date: Wed, 20 Sep 2023 09:32:38 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Linus Torvalds <torvalds@...ux-foundation.org>,
John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
Peter Zijlstra <peterz@...radead.org>,
Matthew Wilcox <willy@...radead.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,
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>,
Anton Ivanov <anton.ivanov@...bridgegreys.com>,
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
* Steven Rostedt <rostedt@...dmis.org> wrote:
> On Tue, 19 Sep 2023 20:31:50 +0200
> Thomas Gleixner <tglx@...utronix.de> wrote:
>
> > The removal of cond_resched() might cause latencies, but then I doubt
> > that these museus pieces are used for real work :)
>
> We could simply leave the cond_resched() around but defined as nops for
> everything but the "nostalgia club" to keep them from having any regressions.
That's not a good idea IMO, it's an invitation for accelerated rate bitrot
turning cond_resched() meaningless very quickly.
We should remove cond_resched() - but probably not as the first step. They
are conceptually independent of NEED_RESCHED_LAZY and we don't *have to*
remove them straight away.
By removing cond_resched() separately there's an easily bisectable point to
blame for any longer latencies on legacy platforms, should any of them
still be used with recent kernels.
Thanks,
Ingo
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