Re: [RFC 1/1] io_uring: process requests completed with -EAGAIN on poll list

[Jens Axboe <axboe@kernel.dk>]

On 4/2/20 12:54 PM, Bijan Mottahedeh wrote:
> A request that completes with an -EAGAIN result after it has been added
> to the poll list, will not be removed from that list in io_do_iopoll()
> because the f_op->iopoll() will not succeed for that request.
> 
> Maintain a retryable local list similar to the done list, and explicity
> reissue requests with an -EAGAIN result.

I think this looks reasonable. You could make the loop here:

> +static void io_iopoll_queue(struct list_head *again)
> +{
> +	struct io_kiocb *req;
> +
> +	while (!list_empty(again)) {
> +		req = list_first_entry(again, struct io_kiocb, list);
> +		list_del(&req->list);
> +		refcount_inc(&req->refs);
> +		io_queue_async_work(req);
> +	}
> +}

be:
	do {
		req = list_first_entry(again, struct io_kiocb, list);
		list_del(&req->list);
		refcount_inc(&req->refs);
		io_queue_async_work(req);
	} while (!list_empty(again));

as you always enter with it non-empty, at least that eliminates one
check per list.

We could also issue inline again, instead of punting these async. But
probably not worth the bother.

-- 
Jens Axboe