linux-kernel - Re: [PATCH v1 3/6] clocksource/drivers/exynos_mct: Set local timer interrupts as percpu

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Message-ID: <Z+yh2UUwxUz/vRbK@perf>
Date: Wed, 2 Apr 2025 11:32:57 +0900
From: Youngmin Nam <youngmin.nam@...sung.com>
To: William McVicker <willmcvicker@...gle.com>
Cc: John Stultz <jstultz@...gle.com>, Catalin Marinas
	<catalin.marinas@....com>, Will Deacon <will@...nel.org>, Peter Griffin
	<peter.griffin@...aro.org>, André Draszik
	<andre.draszik@...aro.org>, Tudor Ambarus <tudor.ambarus@...aro.org>, Rob
	Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor
	Dooley <conor+dt@...nel.org>, Alim Akhtar <alim.akhtar@...sung.com>, Daniel
	Lezcano <daniel.lezcano@...aro.org>, Thomas Gleixner <tglx@...utronix.de>,
	Saravana Kannan <saravanak@...gle.com>, Krzysztof Kozlowski
	<krzk@...nel.org>, kernel-team@...roid.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-samsung-soc@...r.kernel.org, devicetree@...r.kernel.org,
	tigersoundkim@...il.com
Subject: Re: [PATCH v1 3/6] clocksource/drivers/exynos_mct: Set local timer
 interrupts as percpu

On Tue, Apr 01, 2025 at 09:36:19AM -0700, William McVicker wrote:
> On 03/31/2025, John Stultz wrote:
> > On Mon, Mar 31, 2025 at 4:00 PM 'Will McVicker' via kernel-team
> > <kernel-team@...roid.com> wrote:
> > >
> > > From: Hosung Kim <hosung0.kim@...sung.com>
> > >
> > > The MCT local timers can be used as a per-cpu event timer. To prevent
> > 
> > Can be used, or are used?  If it's an option, is this change important
> > in both cases?
> > 
> > > the timer interrupts from migrating to other CPUs, set the flag
> > > IRQF_PERCPU.
> > 
> > Might be work expanding this a bit to clarify why the interrupts
> > migrating to other cpus is undesired.
> 
> Let me dig into this further to figure out if the IP has a limitation where the
> interrupts need to be handled by the CPU the timer was triggered on or if this
> is just an optimization.
> 
> Any chance you know this @Youngmin?
> 
> Thanks,
> Will
> 

Hi Will.

Yes. In downstream, we’ve been using MCT as the clock event timer instead of the ARM timer.
Setting this flag allows each CPU to handle its own clock events, such as scheduling interrupts.

> > 
> > > Signed-off-by: Hosung Kim <hosung0.kim@...sung.com>
> > > [Original commit from https://android.googlesource.com/kernel/gs/+/03267fad19f093bac979ca78309483e9eb3a8d16]
> > > Signed-off-by: Will McVicker <willmcvicker@...gle.com>
> > 
> > thanks!
> > -john
> 
>