Re: [PATCH 05/11] eventpoll: add ep_poll_queue() loop

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

On 2/4/25 19:46, Jens Axboe wrote:
> If a wait_queue_entry is passed in to epoll_wait(), then utilize this
> new helper for reaping events and/or adding to the epoll waitqueue
> rather than calling the potentially sleeping ep_poll(). It works like
> ep_poll(), except it doesn't block - it either returns the events that
> are already available, or it adds the specified entry to the struct
> eventpoll waitqueue to get a callback when events are triggered. It
> returns -EIOCBQUEUED for that case.
> 
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
>   fs/eventpoll.c | 37 ++++++++++++++++++++++++++++++++++++-
>   1 file changed, 36 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index ecaa5591f4be..a8be0c7110e4 100644
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -2032,6 +2032,39 @@ static int ep_try_send_events(struct eventpoll *ep,
>   	return res;
>   }
>   
> +static int ep_poll_queue(struct eventpoll *ep,
> +			 struct epoll_event __user *events, int maxevents,
> +			 struct wait_queue_entry *wait)
> +{
> +	int res, eavail;
> +
> +	/* See ep_poll() for commentary */
> +	eavail = ep_events_available(ep);
> +	while (1) {
> +		if (eavail) {
> +			res = ep_try_send_events(ep, events, maxevents);
> +			if (res)
> +				return res;
> +		}
> +
> +		eavail = ep_busy_loop(ep, true);

I have doubts we want to busy loop here even if it's just one iteration /
nonblockinf. And there is already napi polling support in io_uring done
from the right for io_uring users spot.

-- 
Pavel Begunkov