Re: [PATCH] io_uring: IORING_OP_TIMEOUT support

[Andres Freund <andres@anarazel.de>]

Hi,

On 2019-09-17 10:03:58 -0600, Jens Axboe wrote:
> There's been a few requests for functionality similar to io_getevents()
> and epoll_wait(), where the user can specify a timeout for waiting on
> events. I deliberately did not add support for this through the system
> call initially to avoid overloading the args, but I can see that the use
> cases for this are valid.

> This adds support for IORING_OP_TIMEOUT. If a user wants to get woken
> when waiting for events, simply submit one of these timeout commands
> with your wait call. This ensures that the application sleeping on the
> CQ ring waiting for events will get woken. The timeout command is passed
> in a pointer to a struct timespec. Timeouts are relative.

Hm. This interface wouldn't allow to to reliably use a timeout waiting for
io_uring_enter(..., min_complete > 1, ING_ENTER_GETEVENTS, ...)
right?

I can easily imagine usecases where I'd want to submit a bunch of ios
and wait for all of their completion to minimize unnecessary context
switches, as all IOs are required to continue. But with a relatively
small timeout, to allow switching to do other work etc.

- Andres