[PATCH v2 0/2] improvements for poll requests

[PATCH v2 0/2] improvements for poll requests

[Xiaoguang Wang]

Echo_server codes can be clone from:
https://codeup.openanolis.cn/codeup/storage/io_uring-echo-server.git
branch is xiaoguangwang/io_uring_multishot. There is a simple HOWTO
in this repository.

Usage:
In server: port 10016, 1000 connections, packet size 16 bytes, and
enable fixed files.
  taskset -c 10 io_uring_echo_server_multi_shot  -f -p 10016 -n 1000 -l 16

In client:
  taskset -c 13,14,15,16 ./echo -addr 11.238.147.21:10016 -n 1000 -size 16

Before this patchset, the tps is like below:
1:15:53 req: 1430425, req/s: 286084.693
11:15:58 req: 1426021, req/s: 285204.079
11:16:03 req: 1416761, req/s: 283352.146
11:16:08 req: 1417969, req/s: 283165.637
11:16:13 req: 1424591, req/s: 285349.915
11:16:18 req: 1418706, req/s: 283738.725
11:16:23 req: 1411988, req/s: 282399.052
11:16:28 req: 1419097, req/s: 283820.477
11:16:33 req: 1417816, req/s: 283563.262
11:16:38 req: 1422461, req/s: 284491.702
11:16:43 req: 1418176, req/s: 283635.327
11:16:48 req: 1414525, req/s: 282905.276
11:16:53 req: 1415624, req/s: 283124.140
11:16:58 req: 1426435, req/s: 284970.486

with this patchset:
2021/09/24 11:10:01 start to do client
11:10:06 req: 1444979, req/s: 288995.300
11:10:11 req: 1442559, req/s: 288511.689
11:10:16 req: 1427253, req/s: 285450.390
11:10:21 req: 1445236, req/s: 288349.853
11:10:26 req: 1423949, req/s: 285480.941
11:10:31 req: 1445304, req/s: 289060.815
11:10:36 req: 1441036, req/s: 288207.119
11:10:41 req: 1441117, req/s: 288220.695
11:10:46 req: 1441451, req/s: 288292.731
11:10:51 req: 1438801, req/s: 287759.157
11:10:56 req: 1433227, req/s: 286646.338
11:11:01 req: 1438307, req/s: 287661.577

about 1.3% tps improvements.

Changes in v2:
  I dropped the poll request completion batching patch in V1, since
it shows performance fluctuations, hard to say whether it's useful.

Xiaoguang Wang (2):
  io_uring: reduce frequent add_wait_queue() overhead for multi-shot
    poll request
  io_uring: don't get completion_lock in io_poll_rewait()

 fs/io_uring.c | 66 ++++++++++++++++++++++++++++++++---------------------------
 1 file changed, 36 insertions(+), 30 deletions(-)

-- 
2.14.4.44.g2045bb6

[PATCH v2 1/2] io_uring: reduce frequent add_wait_queue() overhead for multi-shot poll request

[Xiaoguang Wang]

Run echo_server to evaluate io_uring's multi-shot poll performance, perf
shows that add_wait_queue() has obvious overhead. Intruduce a new state
'active' in io_poll_iocb to indicate whether io_poll_wake() should queue
a task_work. This new state will be set to true initially, be set to false
when starting to queue a task work, and be set to true again when a poll
cqe has been committed. One concern is that this method may lost waken-up
event, but seems it's ok.

  io_poll_wake                io_poll_task_func
t1                       |
t2                       |    WRITE_ONCE(req->poll.active, true);
t3                       |
t4                       |    io_commit_cqring(ctx);
t5                       |
t6                       |

If waken-up events happens before or at t4, it's ok, user app will always
see a cqe. If waken-up events happens after t4 and IIUC, io_poll_wake()
will see the new req->poll.active value by using READ_ONCE().

Echo_server codes can be cloned from:
https://codeup.openanolis.cn/codeup/storage/io_uring-echo-server.git,
branch is xiaoguangwang/io_uring_multishot.

Without this patch, the tps in our test environment is 284116, with
this patch, the tps is 287832, about 1.3% reqs improvement, which
is indeed in accord with the saved add_wait_queue() cost.

Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
---
 fs/io_uring.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 7bfd2d00d4fc..7fc52a7f6f05 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -488,6 +488,7 @@ struct io_poll_iocb {
 	__poll_t			events;
 	bool				done;
 	bool				canceled;
+	bool				active;
 	struct wait_queue_entry		wait;
 };
 
@@ -5248,8 +5249,6 @@ static int __io_async_wake(struct io_kiocb *req, struct io_poll_iocb *poll,
 
 	trace_io_uring_task_add(req->ctx, req->opcode, req->user_data, mask);
 
-	list_del_init(&poll->wait.entry);
-
 	req->result = mask;
 	req->io_task_work.func = func;
 
@@ -5280,7 +5279,10 @@ static bool io_poll_rewait(struct io_kiocb *req, struct io_poll_iocb *poll)
 
 	spin_lock(&ctx->completion_lock);
 	if (!req->result && !READ_ONCE(poll->canceled)) {
-		add_wait_queue(poll->head, &poll->wait);
+		if (req->opcode == IORING_OP_POLL_ADD)
+			WRITE_ONCE(req->poll.active, true);
+		else
+			add_wait_queue(poll->head, &poll->wait);
 		return true;
 	}
 
@@ -5356,6 +5358,9 @@ static inline bool io_poll_complete(struct io_kiocb *req, __poll_t mask)
 	return done;
 }
 
+static bool __io_poll_remove_one(struct io_kiocb *req,
+				 struct io_poll_iocb *poll, bool do_cancel);
+
 static void io_poll_task_func(struct io_kiocb *req, bool *locked)
 {
 	struct io_ring_ctx *ctx = req->ctx;
@@ -5369,10 +5374,11 @@ static void io_poll_task_func(struct io_kiocb *req, bool *locked)
 		done = __io_poll_complete(req, req->result);
 		if (done) {
 			io_poll_remove_double(req);
+			__io_poll_remove_one(req, io_poll_get_single(req), true);
 			hash_del(&req->hash_node);
 		} else {
 			req->result = 0;
-			add_wait_queue(req->poll.head, &req->poll.wait);
+			WRITE_ONCE(req->poll.active, true);
 		}
 		io_commit_cqring(ctx);
 		spin_unlock(&ctx->completion_lock);
@@ -5427,6 +5433,7 @@ static void io_init_poll_iocb(struct io_poll_iocb *poll, __poll_t events,
 	poll->head = NULL;
 	poll->done = false;
 	poll->canceled = false;
+	poll->active = true;
 #define IO_POLL_UNMASK	(EPOLLERR|EPOLLHUP|EPOLLNVAL|EPOLLRDHUP)
 	/* mask in events that we always want/need */
 	poll->events = events | IO_POLL_UNMASK;
@@ -5524,6 +5531,7 @@ static int io_async_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
 	trace_io_uring_poll_wake(req->ctx, req->opcode, req->user_data,
 					key_to_poll(key));
 
+	list_del_init(&poll->wait.entry);
 	return __io_async_wake(req, poll, key_to_poll(key), io_async_task_func);
 }
 
@@ -5792,6 +5800,10 @@ static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
 	struct io_kiocb *req = wait->private;
 	struct io_poll_iocb *poll = &req->poll;
 
+	if (!READ_ONCE(poll->active))
+		return 0;
+
+	WRITE_ONCE(poll->active, false);
 	return __io_async_wake(req, poll, key_to_poll(key), io_poll_task_func);
 }
 
-- 
2.14.4.44.g2045bb6

[PATCH v2 2/2] io_uring: don't get completion_lock in io_poll_rewait()

[Xiaoguang Wang]

In current implementation, if there are not available events,
io_poll_rewait() just gets completion_lock, and unlocks it in
io_poll_task_func() or io_async_task_func(), which isn't necessary.

Change this logic to let io_poll_task_func() or io_async_task_func()
get the completion_lock lock, this is also a preparation for
later patch, which will batch poll request completion.

Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
---
 fs/io_uring.c | 50 ++++++++++++++++++++++----------------------------
 1 file changed, 22 insertions(+), 28 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 7fc52a7f6f05..1cf0aaaa086e 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5263,10 +5263,7 @@ static int __io_async_wake(struct io_kiocb *req, struct io_poll_iocb *poll,
 }
 
 static bool io_poll_rewait(struct io_kiocb *req, struct io_poll_iocb *poll)
-	__acquires(&req->ctx->completion_lock)
 {
-	struct io_ring_ctx *ctx = req->ctx;
-
 	/* req->task == current here, checking PF_EXITING is safe */
 	if (unlikely(req->task->flags & PF_EXITING))
 		WRITE_ONCE(poll->canceled, true);
@@ -5277,7 +5274,6 @@ static bool io_poll_rewait(struct io_kiocb *req, struct io_poll_iocb *poll)
 		req->result = vfs_poll(req->file, &pt) & poll->events;
 	}
 
-	spin_lock(&ctx->completion_lock);
 	if (!req->result && !READ_ONCE(poll->canceled)) {
 		if (req->opcode == IORING_OP_POLL_ADD)
 			WRITE_ONCE(req->poll.active, true);
@@ -5365,30 +5361,29 @@ static void io_poll_task_func(struct io_kiocb *req, bool *locked)
 {
 	struct io_ring_ctx *ctx = req->ctx;
 	struct io_kiocb *nxt;
+	bool done;
 
-	if (io_poll_rewait(req, &req->poll)) {
-		spin_unlock(&ctx->completion_lock);
-	} else {
-		bool done;
+	if (io_poll_rewait(req, &req->poll))
+		return;
 
-		done = __io_poll_complete(req, req->result);
-		if (done) {
-			io_poll_remove_double(req);
-			__io_poll_remove_one(req, io_poll_get_single(req), true);
-			hash_del(&req->hash_node);
-		} else {
-			req->result = 0;
-			WRITE_ONCE(req->poll.active, true);
-		}
-		io_commit_cqring(ctx);
-		spin_unlock(&ctx->completion_lock);
-		io_cqring_ev_posted(ctx);
+	spin_lock(&ctx->completion_lock);
+	done = __io_poll_complete(req, req->result);
+	if (done) {
+		io_poll_remove_double(req);
+		__io_poll_remove_one(req, io_poll_get_single(req), true);
+		hash_del(&req->hash_node);
+	} else {
+		req->result = 0;
+		WRITE_ONCE(req->poll.active, true);
+	}
+	io_commit_cqring(ctx);
+	spin_unlock(&ctx->completion_lock);
+	io_cqring_ev_posted(ctx);
 
-		if (done) {
-			nxt = io_put_req_find_next(req);
-			if (nxt)
-				io_req_task_submit(nxt, locked);
-		}
+	if (done) {
+		nxt = io_put_req_find_next(req);
+		if (nxt)
+			io_req_task_submit(nxt, locked);
 	}
 }
 
@@ -5507,11 +5502,10 @@ static void io_async_task_func(struct io_kiocb *req, bool *locked)
 
 	trace_io_uring_task_run(req->ctx, req, req->opcode, req->user_data);
 
-	if (io_poll_rewait(req, &apoll->poll)) {
-		spin_unlock(&ctx->completion_lock);
+	if (io_poll_rewait(req, &apoll->poll))
 		return;
-	}
 
+	spin_lock(&ctx->completion_lock);
 	hash_del(&req->hash_node);
 	io_poll_remove_double(req);
 	spin_unlock(&ctx->completion_lock);
-- 
2.14.4.44.g2045bb6

Re: [PATCH v2 0/2] improvements for poll requests

[Xiaoguang Wang]

hello,


Friendly ping.

The method in this patch set can improve multi-shot's performance a bit. 
If you have some free

time, please have a look, thanks.


Regards,

Xiaoguang Wang


> Echo_server codes can be clone from:
> https://codeup.openanolis.cn/codeup/storage/io_uring-echo-server.git
> branch is xiaoguangwang/io_uring_multishot. There is a simple HOWTO
> in this repository.
>
> Usage:
> In server: port 10016, 1000 connections, packet size 16 bytes, and
> enable fixed files.
>    taskset -c 10 io_uring_echo_server_multi_shot  -f -p 10016 -n 1000 -l 16
>
> In client:
>    taskset -c 13,14,15,16 ./echo -addr 11.238.147.21:10016 -n 1000 -size 16
>
> Before this patchset, the tps is like below:
> 1:15:53 req: 1430425, req/s: 286084.693
> 11:15:58 req: 1426021, req/s: 285204.079
> 11:16:03 req: 1416761, req/s: 283352.146
> 11:16:08 req: 1417969, req/s: 283165.637
> 11:16:13 req: 1424591, req/s: 285349.915
> 11:16:18 req: 1418706, req/s: 283738.725
> 11:16:23 req: 1411988, req/s: 282399.052
> 11:16:28 req: 1419097, req/s: 283820.477
> 11:16:33 req: 1417816, req/s: 283563.262
> 11:16:38 req: 1422461, req/s: 284491.702
> 11:16:43 req: 1418176, req/s: 283635.327
> 11:16:48 req: 1414525, req/s: 282905.276
> 11:16:53 req: 1415624, req/s: 283124.140
> 11:16:58 req: 1426435, req/s: 284970.486
>
> with this patchset:
> 2021/09/24 11:10:01 start to do client
> 11:10:06 req: 1444979, req/s: 288995.300
> 11:10:11 req: 1442559, req/s: 288511.689
> 11:10:16 req: 1427253, req/s: 285450.390
> 11:10:21 req: 1445236, req/s: 288349.853
> 11:10:26 req: 1423949, req/s: 285480.941
> 11:10:31 req: 1445304, req/s: 289060.815
> 11:10:36 req: 1441036, req/s: 288207.119
> 11:10:41 req: 1441117, req/s: 288220.695
> 11:10:46 req: 1441451, req/s: 288292.731
> 11:10:51 req: 1438801, req/s: 287759.157
> 11:10:56 req: 1433227, req/s: 286646.338
> 11:11:01 req: 1438307, req/s: 287661.577
>
> about 1.3% tps improvements.
>
> Changes in v2:
>    I dropped the poll request completion batching patch in V1, since
> it shows performance fluctuations, hard to say whether it's useful.
>
> Xiaoguang Wang (2):
>    io_uring: reduce frequent add_wait_queue() overhead for multi-shot
>      poll request
>    io_uring: don't get completion_lock in io_poll_rewait()
>
>   fs/io_uring.c | 66 ++++++++++++++++++++++++++++++++---------------------------
>   1 file changed, 36 insertions(+), 30 deletions(-)
>

Re: [PATCH v2 0/2] improvements for poll requests

[Jens Axboe]

On 9/23/21 10:22 PM, Xiaoguang Wang wrote:
> Echo_server codes can be clone from:
> https://codeup.openanolis.cn/codeup/storage/io_uring-echo-server.git
> branch is xiaoguangwang/io_uring_multishot. There is a simple HOWTO
> in this repository.
> 
> Usage:
> In server: port 10016, 1000 connections, packet size 16 bytes, and
> enable fixed files.
>   taskset -c 10 io_uring_echo_server_multi_shot  -f -p 10016 -n 1000 -l 16
> 
> In client:
>   taskset -c 13,14,15,16 ./echo -addr 11.238.147.21:10016 -n 1000 -size 16
> 
> Before this patchset, the tps is like below:
> 1:15:53 req: 1430425, req/s: 286084.693
> 11:15:58 req: 1426021, req/s: 285204.079
> 11:16:03 req: 1416761, req/s: 283352.146
> 11:16:08 req: 1417969, req/s: 283165.637
> 11:16:13 req: 1424591, req/s: 285349.915
> 11:16:18 req: 1418706, req/s: 283738.725
> 11:16:23 req: 1411988, req/s: 282399.052
> 11:16:28 req: 1419097, req/s: 283820.477
> 11:16:33 req: 1417816, req/s: 283563.262
> 11:16:38 req: 1422461, req/s: 284491.702
> 11:16:43 req: 1418176, req/s: 283635.327
> 11:16:48 req: 1414525, req/s: 282905.276
> 11:16:53 req: 1415624, req/s: 283124.140
> 11:16:58 req: 1426435, req/s: 284970.486
> 
> with this patchset:
> 2021/09/24 11:10:01 start to do client
> 11:10:06 req: 1444979, req/s: 288995.300
> 11:10:11 req: 1442559, req/s: 288511.689
> 11:10:16 req: 1427253, req/s: 285450.390
> 11:10:21 req: 1445236, req/s: 288349.853
> 11:10:26 req: 1423949, req/s: 285480.941
> 11:10:31 req: 1445304, req/s: 289060.815
> 11:10:36 req: 1441036, req/s: 288207.119
> 11:10:41 req: 1441117, req/s: 288220.695
> 11:10:46 req: 1441451, req/s: 288292.731
> 11:10:51 req: 1438801, req/s: 287759.157
> 11:10:56 req: 1433227, req/s: 286646.338
> 11:11:01 req: 1438307, req/s: 287661.577
> 
> about 1.3% tps improvements.
> 
> Changes in v2:
>   I dropped the poll request completion batching patch in V1, since
> it shows performance fluctuations, hard to say whether it's useful.

Sorry for being slow on this one. Can you resend it against
for-5.16/io_uring? It no longer applies. Thanks!

-- 
Jens Axboe