Re: IRQ thread timeouts and affinity

[Thierry Reding]

On Fri, Oct 10, 2025 at 03:38:59PM +0100, Jon Hunter wrote:
> 
> On 10/10/2025 15:18, 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).
> 
> Thierry, do we ever hotplug CPUs on this device? If not, I am wondering if
> something like this, for now, could only be enabled for devices that don't
> hotplug CPUs. Maybe tied to the kernel config (ie. CONFIG_HOTPLUG_CPU)? Just
> a thought ...

I've only had limited exposure to this, so I don't know all of the use-
cases. People can buy these devices and do anything they want with it,
so I think we have to account for the general case.

Thierry

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