Commit 3a0c037b authored by Dylan Yudaken's avatar Dylan Yudaken Committed by Jens Axboe
Browse files

io_uring: batch task_work 



Batching task work up is an important performance optimisation, as
task_work_add is expensive.

In order to keep the semantics replace the task_list with a fake node
while processing the old list, and then do a cmpxchg at the end to see if
there is more work.

Signed-off-by: default avatarDylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220622134028.2013417-6-dylany@fb.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 923d1592

io_uring/io_uring.c

+13 −9
Original line number Diff line number Diff line
@@ -986,11 +986,11 @@ static void ctx_flush_and_put(struct io_ring_ctx *ctx, bool *locked) 
	percpu_ref_put(&ctx->refs);

}





static void handle_tw_list(struct llist_node *node,

			   struct io_ring_ctx **ctx, bool *locked)

			   struct io_ring_ctx **ctx, bool *locked,

			   struct llist_node *last)

{

	do {

	while (node != last) {

		struct llist_node *next = node->next;

		struct io_kiocb *req = container_of(node, struct io_kiocb,

						    io_task_work.node);
@@ -1006,7 +1006,7 @@ static void handle_tw_list(struct llist_node *node, 
		}

		req->io_task_work.func(req, locked);

		node = next;

	} while (node);

	}

}



/**
@@ -1045,11 +1045,15 @@ void tctx_task_work(struct callback_head *cb) 
	struct io_ring_ctx *ctx = NULL;

	struct io_uring_task *tctx = container_of(cb, struct io_uring_task,

						  task_work);

	struct llist_node *node = llist_del_all(&tctx->task_list);



	if (node) {

		handle_tw_list(node, &ctx, &uring_locked);

		cond_resched();

	struct llist_node fake = {};

	struct llist_node *node = io_llist_xchg(&tctx->task_list, &fake);



	handle_tw_list(node, &ctx, &uring_locked, NULL);

	node = io_llist_cmpxchg(&tctx->task_list, &fake, NULL);

	while (node != &fake) {

		node = io_llist_xchg(&tctx->task_list, &fake);

		handle_tw_list(node, &ctx, &uring_locked, &fake);

		node = io_llist_cmpxchg(&tctx->task_list, &fake, NULL);

	}



	ctx_flush_and_put(ctx, &uring_locked);