linux-kernel - Re: [PATCH -next v6 8/8] arm64: entry: Switch to generic IRQ entry

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Message-ID: <xhsmh1pvjkrfb.mognet@vschneid-thinkpadt14sgen2i.remote.csb>
Date: Thu, 27 Feb 2025 22:29:12 +0100
From: Valentin Schneider <vschneid@...hat.com>
To: Mark Rutland <mark.rutland@....com>
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Subject: Re: [PATCH -next v6 8/8] arm64: entry: Switch to generic IRQ entry

On 27/02/25 18:35, Mark Rutland wrote:
> On Thu, Feb 27, 2025 at 07:08:56PM +0100, Valentin Schneider wrote:
>> On 13/02/25 21:00, Jinjie Ruan wrote:
>> > Currently, x86, Riscv, Loongarch use the generic entry. Convert arm64
>> > to use the generic entry infrastructure from kernel/entry/*.
>> > The generic entry makes maintainers' work easier and codes
>> > more elegant.
>> >
>> > Switch arm64 to generic IRQ entry first, which removed duplicate 100+
>> > LOC and make Lazy preemption on arm64 available by adding a
>> > _TIF_NEED_RESCHED_LAZY bit and enabling ARCH_HAS_PREEMPT_LAZY.
>>
>> Just a drive-by comment as I'm interested in lazy preemption for arm64;
>> this series doesn't actually enable lazy preemption, is that for a
>> follow-up with the rest of the generic entry stuff?
>>
>> From a quick glance, it looks like everything is in place for enabling it.
>
> Sorry, there's been some fractured discussion on this on the
> linux-rt-users list:
>
>   https://lore.kernel.org/linux-rt-users/20241216190451.1c61977c@mordecai.tesarici.cz/
>
> The TL;DR is that lazy preemption doesn't actually depend on generic
> entry, and we should be able to enable it on arm64 independently of this
> series. I'd posted a quick hack which Mike Galbraith cleaned up:
>
>   https://lore.kernel.org/linux-rt-users/a198a7dd9076f97b89d8882bb249b3bf303564ef.camel@gmx.de/
>
> ... but that was never posted as a new thread to LAKML.
>

Thanks for the breadcrumbs!

> Would you be happy to take charge and take that patch, test it, and post
> it here (or spin your own working version)? I was happy with the way it
> looks but hadn't had the time for testing and so on.
>

Sure, looks straightforward enough, I'll pick this up.

> I expect that we'll merge the generic entry code too, but having them
> separate is a bit easier for bisection and backporting where people want
> lazy preemption in downstream trees.
>
> Mark.