Re: [PATCH v2] io_uring: enable toggle of iowait usage when waiting on CQEs

[Pavel Begunkov <asml.silence@gmail.com>]

On 3/14/25 18:48, Jens Axboe wrote:
> By default, io_uring marks a waiting task as being in iowait, if it's
> sleeping waiting on events and there are pending requests. This isn't
> necessarily always useful, and may be confusing on non-storage setups
> where iowait isn't expected. It can also cause extra power usage, by

I think this passage hints on controlling iowait stats, and in my opinion
we shouldn't conflate stats and optimisations. Global iowait stats
is there to stay, but ideally we want to never account io_uring as iowait.
That's while there were talks about removing optimisation toggle at all
(and do it as internal cpufreq magic, I suppose).

How about posing it as an optimisation option only and that iowait stat
is a side effect that can change. Explicitly spelling that in the commit
message and in a comment on top of the flag in an attempt to avoid the
uapi regression trap. We'd also need it in the option's man when it's
written. And I'd also add "hint" to the flag name, like
IORING_ENTER_HINT_NO_IOWAIT, as we might need to nop it if anything
changes on the cpufreq side.

-- 
Pavel Begunkov