linux-kernel - Re: [PATCH] ARM: support PREEMPT

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Message-ID: <dbb9955b-b12f-6b4b-d380-1f95d3d9fed6@huawei.com>
Date: Mon, 5 Aug 2024 10:00:01 +0800
From: Jinjie Ruan <ruanjinjie@...wei.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
CC: <arnd@...db.de>, <afd@...com>, <akpm@...ux-foundation.org>,
	<linus.walleij@...aro.org>, <eric.devolder@...cle.com>, <robh@...nel.org>,
	<vincent.whitchurch@...s.com>, <bhe@...hat.com>, <nico@...xnic.net>,
	<ardb@...nel.org>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <linux-arch@...r.kernel.org>
Subject: Re: [PATCH] ARM: support PREEMPT_DYNAMIC



On 2024/8/2 19:44, Russell King (Oracle) wrote:
> On Wed, Jul 31, 2024 at 10:07:53AM +0800, Jinjie Ruan wrote:
>> On 2024/6/20 17:00, Jinjie Ruan wrote:
>>> Enable support for PREEMPT_DYNAMIC on arm32, allowing the preemption model
>>> to be chosen at boot time.
>>>
>>> Similar to arm64, arm32 does not yet use the generic entry code, we must
>>> define our own `sk_dynamic_irqentry_exit_cond_resched`, which will be
>>> enabled/disabled by the common code in kernel/sched/core.c.
>>>
>>> And arm32 use generic preempt.h, so declare
>>> `sk_dynamic_irqentry_exit_cond_resched` if the arch do not use generic
>>> entry. Other architectures which use generic preempt.h but not use generic
>>> entry can benefit from it.
>>>
>>> Test ok with the below cmdline parameters on Qemu versatilepb board:
>>> 	`preempt=none`
>>> 	`preempt=voluntary`
>>> 	`preempt=full`
>>>
>>> Update preempt mode with debugfs interface on above Qemu board is also
>>> tested ok:
>>> 	# cd /sys/kernel/debug/sched
>>> 	# echo none > preempt
>>> 	# echo voluntary > preempt
>>> 	# echo full > preempt
> 
> Do you have a use case for this feature?

Yes, many of our ARM32 products use different preemption models, and it
would be much more convenient if we could configure it at startup.

>