linux-kernel - Re: [PATCH 1/4] sched/preempt: Prepare for supporting !CONFIG_GENERIC

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Message-ID: <20210921135032.GB35846@C02TD0UTHF1T.local>
Date:   Tue, 21 Sep 2021 14:50:32 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        James Morse <james.morse@....com>,
        Quentin Perret <qperret@...gle.com>
Subject: Re: [PATCH 1/4] sched/preempt: Prepare for supporting
 !CONFIG_GENERIC_ENTRY dynamic preemption

On Tue, Sep 21, 2021 at 09:10:10AM +0200, Peter Zijlstra wrote:
> On Tue, Sep 21, 2021 at 01:32:34AM +0200, Frederic Weisbecker wrote:
> > There is no need to force dynamic preemption to depend on the generic
> > entry code. The latter is convenient but not mandatory. An architecture
> > that doesn't support it just need to provide a static call on its
> > kernel IRQ exit preemption path.
> 
> True; but at the same time ARM64 is also moving to generic entry. Mark?

That's the aspiration, but it's going to take a while to rework the
arm64 and common code. So far I've just been focusing on the groundwork
of moving stuff out of asm so that we can see the wood for the trees.

Generally my preference would be to move things over in stages, to avoid
a flag day where there's the potential for many things to break
simultaneously. So if this is relatively self contained, I think it
maybe worthwhile to do on its own, but I don't have very strong feelings
on that.

Thanks,
Mark.