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

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Message-ID: <Z-28sR02GhsNMnlg@google.com>
Date: Wed, 2 Apr 2025 15:39:45 -0700
From: William McVicker <willmcvicker@...gle.com>
To: Youngmin Nam <youngmin.nam@...sung.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 04/02/2025, Youngmin Nam wrote:
> 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.

Thanks for the explanation! I'll integrate this into the commit text.

Regards,
Will

> 
> > > 
> > > > 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
> > 
> >