Re: [PATCH] io_uring: One wqe per wq

[Pavel Begunkov]

On 3/10/23 20:38, Jens Axboe wrote:
> On 3/10/23 1:11 PM, Breno Leitao wrote:
> > Right now io_wq allocates one io_wqe per NUMA node.  As io_wq is now
> > bound to a task, the task basically uses only the NUMA local io_wqe, and
> > almost never changes NUMA nodes, thus, the other wqes are mostly
> > unused.
>
> What if the task gets migrated to a different node? Unless the task
> is pinned to a node/cpumask that is local to that node, it will move
> around freely.

In which case we're screwed anyway and not only for the slow io-wq
path but also with the hot path as rings and all io_uring ctx and
requests won't be migrated locally.

It's also curious whether io-wq workers will get migrated
automatically as they are a part of the thread group.

> I'm not a huge fan of the per-node setup, but I think the reasonings
> given in this patch are a bit too vague and we need to go a bit
> deeper on what a better setup would look like.

--
Pavel Begunkov