Commit 7a778f9d authored Jun 17, 2021 by Pavel Begunkov Committed by Jens Axboe Jun 18, 2021

io_uring: improve in tctx_task_work() resubmission



If task_state is cleared, io_req_task_work_add() will go the slow path
adding a task_work, setting the task_state, waking up the task and so
on. Not to mention it's expensive. tctx_task_work() first clears the
state and then executes all the work items queued, so if any of them
resubmits or adds new task_work items, it would unnecessarily go through
the slow path of io_req_task_work_add().

Let's clear the ->task_state at the end. We still have to check
->task_list for emptiness afterward to synchronise with
io_req_task_work_add(), do that, and set the state back if we're going
to retry, because clearing not-ours task_state on the next iteration
would be buggy.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/1ef72cdac7022adf0cd7ce4bfe3bb5c82a62eb93.1623949695.git.asml.silence@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 16f72070

fs/io_uring.c

+8 −4

Original line number	Diff line number	Diff line
		@@ -1894,8 +1894,6 @@ static void tctx_task_work(struct callback_head *cb)
		struct io_uring_task *tctx = container_of(cb, struct io_uring_task,
		task_work);

		clear_bit(0, &tctx->task_state);

		while (1) {
		struct io_wq_work_node *node;

		@@ -1917,8 +1915,14 @@ static void tctx_task_work(struct callback_head *cb)
		req->task_work.func(&req->task_work);
		node = next;
		}
		if (wq_list_empty(&tctx->task_list)) {
		clear_bit(0, &tctx->task_state);
		if (wq_list_empty(&tctx->task_list))
		break;
		/* another tctx_task_work() is enqueued, yield */
		if (test_and_set_bit(0, &tctx->task_state))
		break;
		}
		cond_resched();
		}