[PATCH 1/2] io_uring: add IOSQE_ASYNC_HYBRID flag for pollable requests

[Hao Xu <haoxu@linux.alibaba.com>]

The current logic of requests with IOSQE_FORCE_ASYNC is first queueing
it to io-worker, then execute it in a synchronous way. For unbound works
like pollable requests(e.g. read/write a socketfd), the io-worker may
stuck there waiting for events for a long time. And thus other works
wait in the list for a long time too.
Let's introduce a new sqe flag IOSQE_ASYNC_HIBRID for unbound works
(currently pollable requests), with this a request will first be queued
to io-worker, then executed in a nonblock try rather than a synchronous
way. Failure of that leads it to arm poll stuff and then the worker can
begin to handle other works.

Suggested-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
---
 fs/io_uring.c                 | 6 +++++-
 include/uapi/linux/io_uring.h | 4 +++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 73135c5c6168..a99f7f46e6d4 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -104,7 +104,8 @@
 #define IORING_MAX_REG_BUFFERS	(1U << 14)
 
 #define SQE_COMMON_FLAGS (IOSQE_FIXED_FILE | IOSQE_IO_LINK | \
-			  IOSQE_IO_HARDLINK | IOSQE_ASYNC)
+			  IOSQE_IO_HARDLINK | IOSQE_ASYNC | \
+			  IOSQE_ASYNC_HYBRID)
 
 #define SQE_VALID_FLAGS	(SQE_COMMON_FLAGS|IOSQE_BUFFER_SELECT|IOSQE_IO_DRAIN)
 
@@ -709,6 +710,7 @@ enum {
 	REQ_F_HARDLINK_BIT	= IOSQE_IO_HARDLINK_BIT,
 	REQ_F_FORCE_ASYNC_BIT	= IOSQE_ASYNC_BIT,
 	REQ_F_BUFFER_SELECT_BIT	= IOSQE_BUFFER_SELECT_BIT,
+	REQ_F_ASYNC_HYBRID_BIT	= IOSQE_ASYNC_HYBRID_BIT,
 
 	/* first byte is taken by user flags, shift it to not overlap */
 	REQ_F_FAIL_BIT		= 8,
@@ -747,6 +749,8 @@ enum {
 	REQ_F_FORCE_ASYNC	= BIT(REQ_F_FORCE_ASYNC_BIT),
 	/* IOSQE_BUFFER_SELECT */
 	REQ_F_BUFFER_SELECT	= BIT(REQ_F_BUFFER_SELECT_BIT),
+	/* IOSQE_ASYNC_HYBRID */
+	REQ_F_ASYNC_HYBRID	= BIT(REQ_F_ASYNC_HYBRID_BIT),
 
 	/* fail rest of links */
 	REQ_F_FAIL		= BIT(REQ_F_FAIL_BIT),
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index c45b5e9a9387..3e49a7dbe636 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -70,6 +70,7 @@ enum {
 	IOSQE_IO_HARDLINK_BIT,
 	IOSQE_ASYNC_BIT,
 	IOSQE_BUFFER_SELECT_BIT,
+	IOSQE_ASYNC_HYBRID_BIT,
 };
 
 /*
@@ -87,7 +88,8 @@ enum {
 #define IOSQE_ASYNC		(1U << IOSQE_ASYNC_BIT)
 /* select buffer from sqe->buf_group */
 #define IOSQE_BUFFER_SELECT	(1U << IOSQE_BUFFER_SELECT_BIT)
-
+/* first force async then arm poll */
+#define IOSQE_ASYNC_HYBRID	(1U << IOSQE_ASYNC_HYBRID_BIT)
 /*
  * io_uring_setup() flags
  */
-- 
2.24.4