Re: io_uring vs CPU hotplug, was Re: [PATCH 5/9] blk-mq: don't set data->ctx and data->hctx in blk_mq_alloc_request_hctx

Christoph Hellwig
2020-05-20T15:31:31Z

On Wed, May 20, 2020 at 09:20:50AM -0600, Jens Axboe wrote:
> Just checked, and it works fine for me. If I create an SQPOLL ring with
> SQ_AFF set and bound to CPU 3, if CPU 3 goes offline, then the kthread
> just appears unbound but runs just fine. When CPU 3 comes online again,
> the mask appears correct.
>
> So don't think there's anything wrong on that side. The affinity is a
> performance optimization, not a correctness issue. Really not much we
> can do if the chosen CPU is offlined, apart from continue to chug along.

Ok, that sounds pretty sensible.