[PATCH v7] io_uring: batch completion in prior_task_list

[Hao Xu <haoxu@xxxxxxxxxxxxxxxxx>]

In previous patches, we have already gathered some tw with
io_req_task_complete() as callback in prior_task_list, let's complete
them in batch while we cannot grab uring lock. In this way, we batch
the req_complete_post path.

Signed-off-by: Hao Xu <haoxu@xxxxxxxxxxxxxxxxx>
---

v6->v7
- use function pointer to reduce the if check everytime running a task
work in handle_prior_tw_list()

 fs/io_uring.c | 68 +++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 61 insertions(+), 7 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index e9c67f19d585..2c0ff1fc6974 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2223,6 +2223,53 @@ static inline unsigned int io_put_rw_kbuf(struct io_kiocb *req)
 	return io_put_kbuf(req, req->kbuf);
 }
 
+static inline void ctx_commit_and_unlock(struct io_ring_ctx *ctx)
+{
+	io_commit_cqring(ctx);
+	spin_unlock(&ctx->completion_lock);
+	io_cqring_ev_posted(ctx);
+}
+
+static inline void io_req_complete_inline(struct io_kiocb *req, s32 res,
+					  u32 cflags)
+{
+		io_req_complete_state(req, res, cflags);
+		io_req_add_compl_list(req);
+}
+
+static void handle_prior_tw_list(struct io_wq_work_node *node, struct io_ring_ctx **ctx,
+				 bool *locked)
+{
+	void (*io_req_complete_func)(struct io_kiocb *, s32, u32);
+
+	do {
+		struct io_wq_work_node *next = node->next;
+		struct io_kiocb *req = container_of(node, struct io_kiocb,
+						    io_task_work.node);
+
+		if (req->ctx != *ctx) {
+			if (unlikely(!*locked) && *ctx)
+				ctx_commit_and_unlock(*ctx);
+			ctx_flush_and_put(*ctx, locked);
+			*ctx = req->ctx;
+			/* if not contended, grab and improve batching */
+			*locked = mutex_trylock(&(*ctx)->uring_lock);
+			percpu_ref_get(&(*ctx)->refs);
+			if (unlikely(!*locked)) {
+				spin_lock(&(*ctx)->completion_lock);
+				io_req_complete_func = __io_req_complete_post;
+			} else {
+				io_req_complete_func = io_req_complete_inline;
+			}
+		}
+		io_req_complete_func(req, req->result, io_put_rw_kbuf(req));
+		node = next;
+	} while (node);
+
+	if (unlikely(!*locked) && *ctx)
+		ctx_commit_and_unlock(*ctx);
+}
+
 static void handle_tw_list(struct io_wq_work_node *node, struct io_ring_ctx **ctx, bool *locked)
 {
 	do {
@@ -2250,21 +2297,28 @@ static void tctx_task_work(struct callback_head *cb)
 						  task_work);
 
 	while (1) {
-		struct io_wq_work_node *node;
+		struct io_wq_work_node *node1, *node2;
 
-		if (!tctx->prior_task_list.first &&
-		    !tctx->task_list.first && locked)
+		if (!tctx->task_list.first &&
+		    !tctx->prior_task_list.first && locked)
 			io_submit_flush_completions(ctx);
 
 		spin_lock_irq(&tctx->task_lock);
-		node= wq_list_merge(&tctx->prior_task_list, &tctx->task_list);
-		if (!node)
+		node1 = tctx->prior_task_list.first;
+		node2 = tctx->task_list.first;
+		INIT_WQ_LIST(&tctx->task_list);
+		INIT_WQ_LIST(&tctx->prior_task_list);
+		if (!node2 && !node1)
 			tctx->task_running = false;
 		spin_unlock_irq(&tctx->task_lock);
-		if (!node)
+		if (!node2 && !node1)
 			break;
 
-		handle_tw_list(node, &ctx, &locked);
+		if (node1)
+			handle_prior_tw_list(node1, &ctx, &locked);
+
+		if (node2)
+			handle_tw_list(node2, &ctx, &locked);
 		cond_resched();
 	}
 
-- 
2.24.4