io_uring: remove priority tw list optimisation

This optimisation has some built in assumptions that make it easy to
introduce bugs. It also does not have clear wins that make it worth keeping.

Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220622134028.2013417-2-dylany@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

5 files changed, 12 insertions, 70 deletions

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 8bc63413fc54..d21d0fc3645b 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -986,44 +986,6 @@ static void ctx_flush_and_put(struct io_ring_ctx *ctx, bool *locked)
 	percpu_ref_put(&ctx->refs);
 }
 
-static void handle_prev_tw_list(struct io_wq_work_node *node,
-				struct io_ring_ctx **ctx, bool *uring_locked)
-{
-	if (*ctx && !*uring_locked)
-		spin_lock(&(*ctx)->completion_lock);
-
-	do {
-		struct io_wq_work_node *next = node->next;
-		struct io_kiocb *req = container_of(node, struct io_kiocb,
-						    io_task_work.node);
-
-		prefetch(container_of(next, struct io_kiocb, io_task_work.node));
-
-		if (req->ctx != *ctx) {
-			if (unlikely(!*uring_locked && *ctx))
-				io_cq_unlock_post(*ctx);
-
-			ctx_flush_and_put(*ctx, uring_locked);
-			*ctx = req->ctx;
-			/* if not contended, grab and improve batching */
-			*uring_locked = mutex_trylock(&(*ctx)->uring_lock);
-			percpu_ref_get(&(*ctx)->refs);
-			if (unlikely(!*uring_locked))
-				io_cq_lock(*ctx);
-		}
-		if (likely(*uring_locked)) {
-			req->io_task_work.func(req, uring_locked);
-		} else {
-			req->cqe.flags = io_put_kbuf_comp(req);
-			__io_req_complete_post(req);
-		}
-		node = next;
-	} while (node);
-
-	if (unlikely(!*uring_locked))
-		io_cq_unlock_post(*ctx);
-}
-
 static void handle_tw_list(struct io_wq_work_node *node,
 			   struct io_ring_ctx **ctx, bool *locked)
 {
@@ -1054,27 +1016,20 @@ void tctx_task_work(struct callback_head *cb)
 						  task_work);
 
 	while (1) {
-		struct io_wq_work_node *node1, *node2;
+		struct io_wq_work_node *node;
 
 		spin_lock_irq(&tctx->task_lock);
-		node1 = tctx->prio_task_list.first;
-		node2 = tctx->task_list.first;
+		node = tctx->task_list.first;
 		INIT_WQ_LIST(&tctx->task_list);
-		INIT_WQ_LIST(&tctx->prio_task_list);
-		if (!node2 && !node1)
+		if (!node)
 			tctx->task_running = false;
 		spin_unlock_irq(&tctx->task_lock);
-		if (!node2 && !node1)
+		if (!node)
 			break;
-
-		if (node1)
-			handle_prev_tw_list(node1, &ctx, &uring_locked);
-		if (node2)
-			handle_tw_list(node2, &ctx, &uring_locked);
+		handle_tw_list(node, &ctx, &uring_locked);
 		cond_resched();
 
-		if (data_race(!tctx->task_list.first) &&
-		    data_race(!tctx->prio_task_list.first) && uring_locked)
+		if (data_race(!tctx->task_list.first) && uring_locked)
 			io_submit_flush_completions(ctx);
 	}
 
@@ -1086,8 +1041,7 @@ void tctx_task_work(struct callback_head *cb)
 }
 
 static void __io_req_task_work_add(struct io_kiocb *req,
-				   struct io_uring_task *tctx,
-				   struct io_wq_work_list *list)
+				   struct io_uring_task *tctx)
 {
 	struct io_ring_ctx *ctx = req->ctx;
 	struct io_wq_work_node *node;
@@ -1095,7 +1049,7 @@ static void __io_req_task_work_add(struct io_kiocb *req,
 	bool running;
 
 	spin_lock_irqsave(&tctx->task_lock, flags);
-	wq_list_add_tail(&req->io_task_work.node, list);
+	wq_list_add_tail(&req->io_task_work.node, &tctx->task_list);
 	running = tctx->task_running;
 	if (!running)
 		tctx->task_running = true;
@@ -1113,7 +1067,8 @@ static void __io_req_task_work_add(struct io_kiocb *req,
 
 	spin_lock_irqsave(&tctx->task_lock, flags);
 	tctx->task_running = false;
-	node = wq_list_merge(&tctx->prio_task_list, &tctx->task_list);
+	node = tctx->task_list.first;
+	INIT_WQ_LIST(&tctx->task_list);
 	spin_unlock_irqrestore(&tctx->task_lock, flags);
 
 	while (node) {
@@ -1129,17 +1084,7 @@ void io_req_task_work_add(struct io_kiocb *req)
 {
 	struct io_uring_task *tctx = req->task->io_uring;
 
-	__io_req_task_work_add(req, tctx, &tctx->task_list);
-}
-
-void io_req_task_prio_work_add(struct io_kiocb *req)
-{
-	struct io_uring_task *tctx = req->task->io_uring;
-
-	if (req->ctx->flags & IORING_SETUP_SQPOLL)
-		__io_req_task_work_add(req, tctx, &tctx->prio_task_list);
-	else
-		__io_req_task_work_add(req, tctx, &tctx->task_list);
+	__io_req_task_work_add(req, tctx);
 }
 
 static void io_req_tw_post(struct io_kiocb *req, bool *locked)
diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index f026d2670959..f77e4a5403e4 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -36,7 +36,6 @@ struct file *io_file_get_fixed(struct io_kiocb *req, int fd,
 bool io_is_uring_fops(struct file *file);
 bool io_alloc_async_data(struct io_kiocb *req);
 void io_req_task_work_add(struct io_kiocb *req);
-void io_req_task_prio_work_add(struct io_kiocb *req);
 void io_req_tw_post_queue(struct io_kiocb *req, s32 res, u32 cflags);
 void io_req_task_queue(struct io_kiocb *req);
 void io_queue_iowq(struct io_kiocb *req, bool *dont_use);
diff --git a/io_uring/rw.c b/io_uring/rw.c
index e07f2670dfa8..ade3e235f277 100644
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -215,7 +215,7 @@ static void io_complete_rw(struct kiocb *kiocb, long res)
 		return;
 	io_req_set_res(req, res, 0);
 	req->io_task_work.func = io_req_task_complete;
-	io_req_task_prio_work_add(req);
+	io_req_task_work_add(req);
 }
 
 static void io_complete_rw_iopoll(struct kiocb *kiocb, long res)
diff --git a/io_uring/tctx.c b/io_uring/tctx.c
index 9b30fb0d3603..7a68ba9beec3 100644
--- a/io_uring/tctx.c
+++ b/io_uring/tctx.c
@@ -88,7 +88,6 @@ __cold int io_uring_alloc_task_context(struct task_struct *task,
 	task->io_uring = tctx;
 	spin_lock_init(&tctx->task_lock);
 	INIT_WQ_LIST(&tctx->task_list);
-	INIT_WQ_LIST(&tctx->prio_task_list);
 	init_task_work(&tctx->task_work, tctx_task_work);
 	return 0;
 }
diff --git a/io_uring/tctx.h b/io_uring/tctx.h
index dead0ed00429..c8566ea5dca4 100644
--- a/io_uring/tctx.h
+++ b/io_uring/tctx.h
@@ -22,7 +22,6 @@ struct io_uring_task {
 		spinlock_t		task_lock;
 		bool			task_running;
 		struct io_wq_work_list	task_list;
-		struct io_wq_work_list	prio_task_list;
 		struct callback_head	task_work;
 	} ____cacheline_aligned_in_smp;
 };