Re: IRQ thread timeouts and affinity

On Fri, Oct 10, 2025 at 03:38:59PM +0100, Jon Hunter wrote:

On 10/10/2025 15:18, Marc Zyngier wrote:

...

quoted

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