linux-kernel - Re: IRQ thread timeouts and affinity

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Message-ID: <87sefpoj10.wl-maz@kernel.org>
Date: Sat, 11 Oct 2025 11:00:11 +0100
From: Marc Zyngier <maz@...nel.org>
To: Thierry Reding <thierry.reding@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
	linux-tegra@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: IRQ thread timeouts and affinity

On Fri, 10 Oct 2025 16:03:01 +0100,
Thierry Reding <thierry.reding@...il.com> wrote:
> 
> On Fri, Oct 10, 2025 at 03:18:13PM +0100, Marc Zyngier wrote:
> > 
> > CPU hotplug is the main area of concern, and I'm pretty sure it breaks
> > this distribution mechanism (or the other way around). Another thing
> > is that if firmware isn't aware that 1:N interrupts can (or should)
> > wake-up a CPU from sleep, bad things will happen. Given that nobody
> > uses 1:N, you can bet that any bit of privileged SW (TF-A,
> > hypervisors) is likely to be buggy (I've already spotted bugs in KVM
> > around this).
> 
> Okay, I can find out if CPU hotplug is a common use-case on these
> devices, or if we can run some tests with that.

It's not so much whether CPU hotplug is of any use to your particular
box, but whether this has any detrimental impact on *any* machine
doing CPU hotplug.

To be clear, this stuff doesn't go in if something breaks, no matter
how small.

	M.

-- 
Without deviation from the norm, progress is not possible.