[PATCH] io_uring/nop: add IORING_NOP_TW completion flag

[Jens Axboe <axboe@kernel.dk>]

To test and profile the overhead of io_uring task_work and the various
types of it, add IORING_NOP_TW which tells nop to signal completions
through task_work rather than complete them inline.

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

---

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index cfd17e382082..8c3d43caab02 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -449,6 +449,7 @@ enum io_uring_msg_ring_flags {
 #define IORING_NOP_FILE			(1U << 1)
 #define IORING_NOP_FIXED_FILE		(1U << 2)
 #define IORING_NOP_FIXED_BUFFER		(1U << 3)
+#define IORING_NOP_TW			(1U << 4)
 
 /*
  * IO completion data structure (Completion Queue Entry)
diff --git a/io_uring/nop.c b/io_uring/nop.c
index 6ac2de761fd3..20ed0f85b1c2 100644
--- a/io_uring/nop.c
+++ b/io_uring/nop.c
@@ -20,7 +20,8 @@ struct io_nop {
 };
 
 #define NOP_FLAGS	(IORING_NOP_INJECT_RESULT | IORING_NOP_FIXED_FILE | \
-			 IORING_NOP_FIXED_BUFFER | IORING_NOP_FILE)
+			 IORING_NOP_FIXED_BUFFER | IORING_NOP_FILE | \
+			 IORING_NOP_TW)
 
 int io_nop_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
@@ -68,5 +69,10 @@ int io_nop(struct io_kiocb *req, unsigned int issue_flags)
 	if (ret < 0)
 		req_set_fail(req);
 	io_req_set_res(req, nop->result, 0);
+	if (nop->flags & IORING_NOP_TW) {
+		req->io_task_work.func = io_req_task_complete;
+		io_req_task_work_add(req);
+		return IOU_ISSUE_SKIP_COMPLETE;
+	}
 	return IOU_COMPLETE;
 }

-- 
Jens Axboe