Commit e9979b36 authored by Pavel Begunkov's avatar Pavel Begunkov Committed by Jens Axboe
Browse files

io_uring: skip futile iopoll iterations 



The only way to get out of io_iopoll_getevents() and continue iterating
is to have empty iopoll_list, otherwise the main loop would just exit.
So, instead of the unlock on 8th time heuristic, do that based on
iopoll_list.

Also, as no one can add new requests to iopoll_list while
io_iopoll_check() hold uring_lock, it's useless to spin with the list
empty, return in that case.

Signed-off-by: default avatarPavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/5b8ebe84f5fff7ffa1f708952dfef7fc78b668e2.1618278933.git.asml.silence@gmail.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent cce4b8b0

fs/io_uring.c

+5 −2
Original line number Diff line number Diff line
@@ -2385,7 +2385,7 @@ static void io_iopoll_try_reap_events(struct io_ring_ctx *ctx) 
static int io_iopoll_check(struct io_ring_ctx *ctx, long min)

{

	unsigned int nr_events = 0;

	int iters = 0, ret = 0;

	int ret = 0;



	/*

	 * We disallow the app entering submit/complete with polling, but we
@@ -2414,10 +2414,13 @@ static int io_iopoll_check(struct io_ring_ctx *ctx, long min) 
		 * forever, while the workqueue is stuck trying to acquire the

		 * very same mutex.

		 */

		if (!(++iters & 7)) {

		if (list_empty(&ctx->iopoll_list)) {

			mutex_unlock(&ctx->uring_lock);

			io_run_task_work();

			mutex_lock(&ctx->uring_lock);



			if (list_empty(&ctx->iopoll_list))

				break;

		}



		ret = io_iopoll_getevents(ctx, &nr_events, min);