Re: Question on handling managed IRQs when hotplugging CPUs

Thomas Gleixner
2019-02-01T21:57:59Z

On Fri, 1 Feb 2019, Hannes Reinecke wrote:
> Thing is, if we have _managed_ CPU hotplug (ie if the hardware provides some
> means of quiescing the CPU before hotplug) then the whole thing is trivial;
> disable SQ and wait for all outstanding commands to complete.
> Then trivially all requests are completed and the issue is resolved.
> Even with todays infrastructure.
>
> And I'm not sure if we can handle surprise CPU hotplug at all, given all the
> possible race conditions.
> But then I might be wrong.

The kernel would completely fall apart when a CPU would vanish by surprise,
i.e. uncontrolled by the kernel. Then the SCSI driver exploding would be
the least of our problems.

Thanks,

tglx