RE: [PATCH v2 0/8] x86, sched, mm: Speed up CPU hotplug on large systems

[Luck, Tony]

> Benchmark workload (mean of 10 runs per step):
>
>  # echo 1 > /sys/kernel/rcu_expedited
>  # for i in {1..N}; do echo 0 > /sys/devices/system/cpu/cpu$i/online; done

Side question. Have you had issues with this step failing on large systems with "smart" I/O
devices that support many interrupt vectors?

Some validation folks inside Intel had some tests that looped taking all CPUs offline and
bringing them back. They complained starting around Sapphire Rapids this their test
would get down to just CPU 0 and CPU 1 and fail to take CPU 1 offline because there
were too many interrupts to fit into just a single CPUs available vectors.

It was a while ago, so maybe something changed in interrupt code to handle this.

-Tony