linux-kernel - Re: [PATCH -next v7 5/7] arm64: entry: Refactor preempt_schedule

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Message-ID: <ced13246-4c00-4837-9d8a-1d140eb0bcb3@arm.com>
Date: Mon, 11 Aug 2025 17:02:25 +0100
From: Ada Couprie Diaz <ada.coupriediaz@....com>
To: Jinjie Ruan <ruanjinjie@...wei.com>
Cc: catalin.marinas@....com, will@...nel.org, oleg@...hat.com,
 sstabellini@...nel.org, mark.rutland@....com, puranjay@...nel.org,
 broonie@...nel.org, mbenes@...e.cz, ryan.roberts@....com,
 akpm@...ux-foundation.org, chenl311@...natelecom.cn,
 anshuman.khandual@....com, kristina.martsenko@....com,
 liaochang1@...wei.com, ardb@...nel.org, leitao@...ian.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 xen-devel@...ts.xenproject.org, Ada Couprie Diaz <ada.coupriediaz@....com>
Subject: Re: [PATCH -next v7 5/7] arm64: entry: Refactor
 preempt_schedule_irq() check code

On 06/08/2025 07:39, Jinjie Ruan wrote:

> On 2025/8/5 23:06, Ada Couprie Diaz wrote:
>> Hi Jinjie,
>>
>> On 29/07/2025 02:54, Jinjie Ruan wrote:
>>> ARM64 requires an additional check whether to reschedule on return
>>> from interrupt. So add arch_irqentry_exit_need_resched() as the default
>>> NOP implementation and hook it up into the need_resched() condition in
>>> raw_irqentry_exit_cond_resched(). This allows ARM64 to implement
>>> the architecture specific version for switching over to
>>> the generic entry code.
>>> [...]
>> I've had some trouble reviewing this patch : on the one hand because
>> I didn't notice `arch_irqentry_exit_need_resched()` was added in
>> the common entry code, which is on me !
>> On the other hand, I felt that the patch itself was a bit disconnected :
>> we add `arch_irqentry_exit_need_resched()` in the common entry code,
>> with a default NOP, but in the same function we add to arm64,
>> while mentioning that this is for arm64's additional checks,
>> which we only implement in patch 7.
> Yes, it does.
>
>> Would it make sense to move the `arch_irqentry_exit_need_resched()`
>> part of the patch to patch 7, so that the introduction and
>> arch-specific implementation appear together ?
>> To me it seems easier to wrap my head around, as it would look like
>> "Move arm64 to generic entry, but it does additional checks : add a new
>> arch-specific function controlling re-scheduling, defaulting to true,
>> and implement it for arm64". I feel it could help making patch 7's
>> commit message clearer as well.
>>
>>  From what I gathered on the archive `arch_irqentry_exit_need_resched()`
>> being added here was suggested previously, so others might not have the
>> same opinion.
> Yes, introduce `arch_irqentry_exit_need_resched()` here may help
> understand the patch's refactoring purpose.
I can see that as well.
I shared my opinion in case it could be useful, but as I mentioned
in my reply to the cover : it's not a big issue and I'm happy for
`arch_irqentry_exit_need_resched()` to be implemented here if that
makes more sense !
>> Maybe improving the commit message and comment for this would be enough
>> as well, as per my suggestions above.
> Thank you! I'll improve the commit message and comment.
>
My pleasure !
Ada