[PATCH net-next v6 0/5] net/smc: Optimizing performance in short-lived scenarios

From: "D. Wythe" <alibuda@linux.alibaba.com>

This patch set aims to optimizing performance of SMC in short-lived
links scenarios, which is quite unsatisfactory right now.

In our benchmark, we test it with follow scripts:

./wrk -c 10000 -t 4 -H 'Connection: Close' -d 20 http://smc-server

Current performance figures like that:

Running 20s test @ http://11.213.45.6
  4 threads and 10000 connections
  4956 requests in 20.06s, 3.24MB read
  Socket errors: connect 0, read 0, write 672, timeout 0
Requests/sec:    247.07
Transfer/sec:    165.28KB

There are many reasons for this phenomenon, this patch set doesn't
solve it all though, but it can be well alleviated with it in.

Patch 1/5  (Make smc_tcp_listen_work() independent) :

Separate smc_tcp_listen_work() from smc_listen_work(), make them
independent of each other, the busy SMC handshake can not affect new TCP
connections visit any more. Avoid discarding a large number of TCP
connections after being overstock, which is undoubtedly raise the
connection establishment time.

Patch 2/5 (Limits SMC backlog connections):

Since patch 1 has separated smc_tcp_listen_work() from
smc_listen_work(), an unrestricted TCP accept have come into being. This
patch try to put a limit on SMC backlog connections refers to
implementation of TCP.

Patch 3/5 (Fallback when SMC handshake workqueue congested):

Considering the complexity of SMC handshake right now, in short-lived
links scenarios, this may not be the main scenario of SMC though, it's
performance is still quite poor. This Patch try to provide auto fallback
case when SMC handshake workqueue congested, which is the sign of SMC
handshake stacking in our opinion.

Patch 4/5 (Dynamic control SMC auto fallback by socket options)

This patch allow applications dynamically control the ability of SMC
auto fallback. Since SMC don't support set SMC socket option before,
this patch also have to support SMC's owns socket options.

Patch 5/5 (Add global configure for auto fallback by netlink)

This patch provides a way to get benefit of auto fallback without
modifying any code for applications, which is quite useful for most
existing applications.

After this patch set, performance figures like that:

Running 20s test @ http://11.213.45.6
  4 threads and 10000 connections
  693253 requests in 20.10s, 452.88MB read
Requests/sec:  34488.13
Transfer/sec:     22.53MB

That's a quite well performance improvement, about to 6 to 7 times in my
environment.
---
changelog:
v2 -> v1:
- fix compile warning
- fix invalid dependencies in kconfig
v3 -> v2:
- correct spelling mistakes
- fix useless variable declare
v4 -> v3
- make smc_tcp_ls_wq be static
v5 -> v4
- add dynamic control for SMC auto fallback by socket options
- add global configure for SMC auto fallback through netlink
v6 -> v5
- move auto fallback to net namespace scope
- remove auto fallback attribute in SMC_GEN_SYS_INFO 
- add independent attributes for auto fallback
---
D. Wythe (5):
  net/smc: Make smc_tcp_listen_work() independent
  net/smc: Limit backlog connections
  net/smc: Fallback when handshake workqueue congested
  net/smc: Dynamic control auto fallback by socket options
  net/smc: Add global configure for auto fallback by netlink

 include/linux/socket.h   |   1 +
 include/linux/tcp.h      |   1 +
 include/net/netns/smc.h  |   2 +
 include/uapi/linux/smc.h |  15 ++++
 net/ipv4/tcp_input.c     |   3 +-
 net/smc/af_smc.c         | 182 ++++++++++++++++++++++++++++++++++++++++++++++-
 net/smc/smc.h            |  11 +++
 net/smc/smc_netlink.c    |  15 ++++
 net/smc/smc_pnet.c       |   3 +
 9 files changed, 230 insertions(+), 3 deletions(-)

-- 
1.8.3.1

From: "D. Wythe" <alibuda@linux.alibaba.com>

In multithread and 10K connections benchmark, the backend TCP connection
established very slowly, and lots of TCP connections stay in SYN_SENT
state.

Client: smc_run wrk -c 10000 -t 4 http://server

the netstate of server host shows like:
    145042 times the listen queue of a socket overflowed
    145042 SYNs to LISTEN sockets dropped

One reason of this issue is that, since the smc_tcp_listen_work() shared
the same workqueue (smc_hs_wq) with smc_listen_work(), while the
smc_listen_work() do blocking wait for smc connection established. Once
the workqueue became congested, it's will block the accept() from TCP
listen.

This patch creates a independent workqueue(smc_tcp_ls_wq) for
smc_tcp_listen_work(), separate it from smc_listen_work(), which is
quite acceptable considering that smc_tcp_listen_work() runs very fast.

Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
---
 net/smc/af_smc.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index 00b2e9d..4969ac8 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c

@@ -59,6 +59,7 @@
 						 * creation on client
 						 */
 
+static struct workqueue_struct	*smc_tcp_ls_wq;	/* wq for tcp listen work */
 struct workqueue_struct	*smc_hs_wq;	/* wq for handshake work */
 struct workqueue_struct	*smc_close_wq;	/* wq for close work */
 

@@ -2227,7 +2228,7 @@ static void smc_clcsock_data_ready(struct sock *listen_clcsock)
 	lsmc->clcsk_data_ready(listen_clcsock);
 	if (lsmc->sk.sk_state == SMC_LISTEN) {
 		sock_hold(&lsmc->sk); /* sock_put in smc_tcp_listen_work() */
-		if (!queue_work(smc_hs_wq, &lsmc->tcp_listen_work))
+		if (!queue_work(smc_tcp_ls_wq, &lsmc->tcp_listen_work))
 			sock_put(&lsmc->sk);
 	}
 }

@@ -3024,9 +3025,14 @@ static int __init smc_init(void)
 		goto out_nl;
 
 	rc = -ENOMEM;
+
+	smc_tcp_ls_wq = alloc_workqueue("smc_tcp_ls_wq", 0, 0);
+	if (!smc_tcp_ls_wq)
+		goto out_pnet;
+
 	smc_hs_wq = alloc_workqueue("smc_hs_wq", 0, 0);
 	if (!smc_hs_wq)
-		goto out_pnet;
+		goto out_alloc_tcp_ls_wq;
 
 	smc_close_wq = alloc_workqueue("smc_close_wq", 0, 0);
 	if (!smc_close_wq)

@@ -3097,6 +3103,8 @@ static int __init smc_init(void)
 	destroy_workqueue(smc_close_wq);
 out_alloc_hs_wq:
 	destroy_workqueue(smc_hs_wq);
+out_alloc_tcp_ls_wq:
+	destroy_workqueue(smc_tcp_ls_wq);
 out_pnet:
 	smc_pnet_exit();
 out_nl:

@@ -3115,6 +3123,7 @@ static void __exit smc_exit(void)
 	smc_core_exit();
 	smc_ib_unregister_client();
 	destroy_workqueue(smc_close_wq);
+	destroy_workqueue(smc_tcp_ls_wq);
 	destroy_workqueue(smc_hs_wq);
 	proto_unregister(&smc_proto6);
 	proto_unregister(&smc_proto);

-- 
1.8.3.1

From: "D. Wythe" <alibuda@linux.alibaba.com>

This patch intends to provide a mechanism to allow automatic fallback to
TCP according to the pressure of SMC handshake process. At present,
frequent visits will cause the incoming connections to be backlogged in
SMC handshake queue, raise the connections established time. Which is
quite unacceptable for those applications who base on short lived
connections.

There are two ways to implement this mechanism:

1. Fallback when TCP established.
2. Fallback before TCP established.

In the first way, we need to wait and receive CLC messages that the
client will potentially send, and then actively reply with a decline
message, in a sense, which is also a sort of SMC handshake, affect the
connections established time on its way.

In the second way, the only problem is that we need to inject SMC logic
into TCP when it is about to reply the incoming SYN, since we already do
that, it's seems not a problem anymore. And advantage is obvious, few
additional processes are required to complete the fallback.

This patch use the second way.

Link: https://lore.kernel.org/all/1641301961-59331-1-git-send-email-alibuda@linux.alibaba.com/
Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
---
 include/linux/tcp.h  |  1 +
 net/ipv4/tcp_input.c |  3 ++-
 net/smc/af_smc.c     | 18 ++++++++++++++++++
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 78b91bb..1c4ae5d 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h

@@ -394,6 +394,7 @@ struct tcp_sock {
 	bool	is_mptcp;
 #endif
 #if IS_ENABLED(CONFIG_SMC)
+	bool	(*smc_in_limited)(const struct sock *sk);
 	bool	syn_smc;	/* SYN includes SMC */
 #endif
 

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index af94a6d..e817ec6 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c

@@ -6703,7 +6703,8 @@ static void tcp_openreq_init(struct request_sock *req,
 	ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
 	ireq->ir_mark = inet_request_mark(sk, skb);
 #if IS_ENABLED(CONFIG_SMC)
-	ireq->smc_ok = rx_opt->smc_ok;
+	ireq->smc_ok = rx_opt->smc_ok && !(tcp_sk(sk)->smc_in_limited &&
+			tcp_sk(sk)->smc_in_limited(sk));
 #endif
 }
 

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index ebfce3d..8175f60 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c

@@ -101,6 +101,22 @@ static struct sock *smc_tcp_syn_recv_sock(const struct sock *sk, struct sk_buff
 	return NULL;
 }
 
+static bool smc_is_in_limited(const struct sock *sk)
+{
+	const struct smc_sock *smc;
+
+	smc = (const struct smc_sock *)
+		((uintptr_t)sk->sk_user_data & ~SK_USER_DATA_NOCOPY);
+
+	if (!smc)
+		return true;
+
+	if (workqueue_congested(WORK_CPU_UNBOUND, smc_hs_wq))
+		return true;
+
+	return false;
+}
+
 static struct smc_hashinfo smc_v4_hashinfo = {
 	.lock = __RW_LOCK_UNLOCKED(smc_v4_hashinfo.lock),
 };

@@ -2309,6 +2325,8 @@ static int smc_listen(struct socket *sock, int backlog)
 
 	inet_csk(smc->clcsock->sk)->icsk_af_ops = &smc->af_ops;
 
+	tcp_sk(smc->clcsock->sk)->smc_in_limited = smc_is_in_limited;
+
 	rc = kernel_listen(smc->clcsock, backlog);
 	if (rc) {
 		smc->clcsock->sk->sk_data_ready = smc->clcsk_data_ready;

-- 
1.8.3.1

From: "D. Wythe" <alibuda@linux.alibaba.com>

Current implementation does not handling backlog semantics, one
potential risk is that server will be flooded by infinite amount
connections, even if client was SMC-incapable.

This patch works to put a limit on backlog connections, referring to the
TCP implementation, we divides SMC connections into two categories:

1. Half SMC connection, which includes all TCP established while SMC not
connections.

2. Full SMC connection, which includes all SMC established connections.

For half SMC connection, since all half SMC connections starts with TCP
established, we can achieve our goal by put a limit before TCP
established. Refer to the implementation of TCP, this limits will based
on not only the half SMC connections but also the full connections,
which is also a constraint on full SMC connections.

For full SMC connections, although we know exactly where it starts, it's
quite hard to put a limit before it. The easiest way is to block wait
before receive SMC confirm CLC message, while it's under protection by
smc_server_lgr_pending, a global lock, which leads this limit to the
entire host instead of a single listen socket. Another way is to drop
the full connections, but considering the cast of SMC connections, we
prefer to keep full SMC connections.

Even so, the limits of full SMC connections still exists, see commits
about half SMC connection below.

After this patch, the limits of backend connection shows like:

For SMC:

1. Client with SMC-capability can makes 2 * backlog full SMC connections
   or 1 * backlog half SMC connections and 1 * backlog full SMC
   connections at most.

2. Client without SMC-capability can only makes 1 * backlog half TCP
   connections and 1 * backlog full TCP connections.

Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
---
 net/smc/af_smc.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 net/smc/smc.h    |  4 ++++
 2 files changed, 47 insertions(+)

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index 4969ac8..ebfce3d 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c

@@ -73,6 +73,34 @@ static void smc_set_keepalive(struct sock *sk, int val)
 	smc->clcsock->sk->sk_prot->keepalive(smc->clcsock->sk, val);
 }
 
+static struct sock *smc_tcp_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
+					  struct request_sock *req,
+					  struct dst_entry *dst,
+					  struct request_sock *req_unhash,
+					  bool *own_req)
+{
+	struct smc_sock *smc;
+
+	smc = (struct smc_sock *)((uintptr_t)sk->sk_user_data & ~SK_USER_DATA_NOCOPY);
+
+	if (READ_ONCE(sk->sk_ack_backlog) + atomic_read(&smc->smc_pendings) >
+				sk->sk_max_ack_backlog)
+		goto drop;
+
+	if (sk_acceptq_is_full(&smc->sk)) {
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
+		goto drop;
+	}
+
+	/* passthrough to origin syn recv sock fct */
+	return smc->ori_af_ops->syn_recv_sock(sk, skb, req, dst, req_unhash, own_req);
+
+drop:
+	dst_release(dst);
+	tcp_listendrop(sk);
+	return NULL;
+}
+
 static struct smc_hashinfo smc_v4_hashinfo = {
 	.lock = __RW_LOCK_UNLOCKED(smc_v4_hashinfo.lock),
 };

@@ -1595,6 +1623,9 @@ static void smc_listen_out(struct smc_sock *new_smc)
 	struct smc_sock *lsmc = new_smc->listen_smc;
 	struct sock *newsmcsk = &new_smc->sk;
 
+	if (tcp_sk(new_smc->clcsock->sk)->syn_smc)
+		atomic_dec(&lsmc->smc_pendings);
+
 	if (lsmc->sk.sk_state == SMC_LISTEN) {
 		lock_sock_nested(&lsmc->sk, SINGLE_DEPTH_NESTING);
 		smc_accept_enqueue(&lsmc->sk, newsmcsk);

@@ -2200,6 +2231,9 @@ static void smc_tcp_listen_work(struct work_struct *work)
 		if (!new_smc)
 			continue;
 
+		if (tcp_sk(new_smc->clcsock->sk)->syn_smc)
+			atomic_inc(&lsmc->smc_pendings);
+
 		new_smc->listen_smc = lsmc;
 		new_smc->use_fallback = lsmc->use_fallback;
 		new_smc->fallback_rsn = lsmc->fallback_rsn;

@@ -2266,6 +2300,15 @@ static int smc_listen(struct socket *sock, int backlog)
 	smc->clcsock->sk->sk_data_ready = smc_clcsock_data_ready;
 	smc->clcsock->sk->sk_user_data =
 		(void *)((uintptr_t)smc | SK_USER_DATA_NOCOPY);
+
+	/* save origin ops */
+	smc->ori_af_ops = inet_csk(smc->clcsock->sk)->icsk_af_ops;
+
+	smc->af_ops = *smc->ori_af_ops;
+	smc->af_ops.syn_recv_sock = smc_tcp_syn_recv_sock;
+
+	inet_csk(smc->clcsock->sk)->icsk_af_ops = &smc->af_ops;
+
 	rc = kernel_listen(smc->clcsock, backlog);
 	if (rc) {
 		smc->clcsock->sk->sk_data_ready = smc->clcsk_data_ready;

diff --git a/net/smc/smc.h b/net/smc/smc.h
index 37b2001..5e5e38d 100644
--- a/net/smc/smc.h
+++ b/net/smc/smc.h

@@ -252,6 +252,10 @@ struct smc_sock {				/* smc sock container */
 	bool			use_fallback;	/* fallback to tcp */
 	int			fallback_rsn;	/* reason for fallback */
 	u32			peer_diagnosis; /* decline reason from peer */
+	atomic_t                smc_pendings;   /* pending smc connections */
+	struct inet_connection_sock_af_ops		af_ops;
+	const struct inet_connection_sock_af_ops	*ori_af_ops;
+						/* origin af ops */
 	int			sockopt_defer_accept;
 						/* sockopt TCP_DEFER_ACCEPT
 						 * value

-- 
1.8.3.1

From: "D. Wythe" <alibuda@linux.alibaba.com>

Although we can control SMC auto fallback through socket options, which
means that applications who need it must modify their code. It's quite
troublesome for many existing applications. This patch modifies the
global default value of auto fallback through netlink, providing a way
to auto fallback without modifying any code for applications.

Suggested-by: Tony Lu <tonylu@linux.alibaba.com>
Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
---
 include/net/netns/smc.h  |  2 ++
 include/uapi/linux/smc.h | 11 +++++++++++
 net/smc/af_smc.c         | 41 +++++++++++++++++++++++++++++++++++++++++
 net/smc/smc.h            |  6 ++++++
 net/smc/smc_netlink.c    | 15 +++++++++++++++
 net/smc/smc_pnet.c       |  3 +++
 6 files changed, 78 insertions(+)

diff --git a/include/net/netns/smc.h b/include/net/netns/smc.h
index ea8a9cf..61646ff 100644
--- a/include/net/netns/smc.h
+++ b/include/net/netns/smc.h

@@ -12,5 +12,7 @@ struct netns_smc {
 	/* protect fback_rsn */
 	struct mutex			mutex_fback_rsn;
 	struct smc_stats_rsn		*fback_rsn;
+
+	bool				auto_fallback;	/* whether allow auto_fallback */
 };
 #endif

diff --git a/include/uapi/linux/smc.h b/include/uapi/linux/smc.h
index 9f2cbf8..28a590d 100644
--- a/include/uapi/linux/smc.h
+++ b/include/uapi/linux/smc.h

@@ -59,6 +59,9 @@ enum {
 	SMC_NETLINK_DUMP_SEID,
 	SMC_NETLINK_ENABLE_SEID,
 	SMC_NETLINK_DISABLE_SEID,
+	SMC_NETLINK_DUMP_AUTO_FALLBACK,
+	SMC_NETLINK_ENABLE_AUTO_FALLBACK,
+	SMC_NETLINK_DISABLE_AUTO_FALLBACK,
 };
 
 /* SMC_GENL_FAMILY top level attributes */

@@ -285,6 +288,14 @@ enum {
 	SMC_NLA_SEID_TABLE_MAX = __SMC_NLA_SEID_TABLE_MAX - 1
 };
 
+/* SMC_NETLINK_AUTO_FALLBACK attributes */
+enum {
+	SMC_NLA_AUTO_FALLBACK_UNSPEC,
+	SMC_NLA_AUTO_FALLBACK_ENABLED,	/* u8 */
+	__SMC_NLA_AUTO_FALLBACK_MAX,
+	SMC_NLA_AUTO_FALLBACK_MAX = __SMC_NLA_AUTO_FALLBACK_MAX - 1
+};
+
 /* SMC socket options */
 #define SMC_AUTO_FALLBACK 1	/* allow auto fallback to TCP */
 

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index c313561..5e56281 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c

@@ -66,6 +66,44 @@
 static void smc_tcp_listen_work(struct work_struct *);
 static void smc_connect_work(struct work_struct *);
 
+int smc_nl_dump_auto_fallback(struct sk_buff *skb, struct netlink_callback *cb)
+{
+	struct smc_nl_dmp_ctx *cb_ctx = smc_nl_dmp_ctx(cb);
+	void *hdr;
+
+	if (cb_ctx->pos[0])
+		goto out;
+
+	hdr = genlmsg_put(skb, NETLINK_CB(cb->skb).portid, cb->nlh->nlmsg_seq,
+			  &smc_gen_nl_family, NLM_F_MULTI,
+			  SMC_NETLINK_DUMP_AUTO_FALLBACK);
+	if (!hdr)
+		return -ENOMEM;
+
+	if (nla_put_u8(skb, SMC_NLA_AUTO_FALLBACK_ENABLED, sock_net(skb->sk)->smc.auto_fallback))
+		goto err;
+
+	genlmsg_end(skb, hdr);
+	cb_ctx->pos[0] = 1;
+out:
+	return skb->len;
+err:
+	genlmsg_cancel(skb, hdr);
+	return -EMSGSIZE;
+}
+
+int smc_nl_enable_auto_fallback(struct sk_buff *skb, struct genl_info *info)
+{
+	sock_net(skb->sk)->smc.auto_fallback = true;
+	return 0;
+}
+
+int smc_nl_disable_auto_fallback(struct sk_buff *skb, struct genl_info *info)
+{
+	sock_net(skb->sk)->smc.auto_fallback = false;
+	return 0;
+}
+
 static void smc_set_keepalive(struct sock *sk, int val)
 {
 	struct smc_sock *smc = smc_sk(sk);

@@ -3006,6 +3044,9 @@ static int __smc_create(struct net *net, struct socket *sock, int protocol,
 	smc->use_fallback = false; /* assume rdma capability first */
 	smc->fallback_rsn = 0;
 
+	/* default behavior from auto_fallback */
+	smc->auto_fallback = net->smc.auto_fallback;
+
 	rc = 0;
 	if (!clcsock) {
 		rc = sock_create_kern(net, family, SOCK_STREAM, IPPROTO_TCP,

diff --git a/net/smc/smc.h b/net/smc/smc.h
index a0bdf75..4cfbd61 100644
--- a/net/smc/smc.h
+++ b/net/smc/smc.h

@@ -14,6 +14,7 @@
 #include <linux/socket.h>
 #include <linux/types.h>
 #include <linux/compiler.h> /* __aligned */
+#include <net/genetlink.h>
 #include <net/sock.h>
 
 #include "smc_ib.h"

@@ -336,4 +337,9 @@ void smc_fill_gid_list(struct smc_link_group *lgr,
 		       struct smc_gidlist *gidlist,
 		       struct smc_ib_device *known_dev, u8 *known_gid);
 
+/* smc auto_fallback interface for netlink */
+int smc_nl_dump_auto_fallback(struct sk_buff *skb, struct netlink_callback *cb);
+int smc_nl_enable_auto_fallback(struct sk_buff *skb, struct genl_info *info);
+int smc_nl_disable_auto_fallback(struct sk_buff *skb, struct genl_info *info);
+
 #endif	/* __SMC_H */

diff --git a/net/smc/smc_netlink.c b/net/smc/smc_netlink.c
index f13ab06..9f3abf7 100644
--- a/net/smc/smc_netlink.c
+++ b/net/smc/smc_netlink.c

@@ -111,6 +111,21 @@
 		.flags = GENL_ADMIN_PERM,
 		.doit = smc_nl_disable_seid,
 	},
+	{
+		.cmd = SMC_NETLINK_DUMP_AUTO_FALLBACK,
+		/* can be retrieved by unprivileged users */
+		.dumpit = smc_nl_dump_auto_fallback,
+	},
+	{
+		.cmd = SMC_NETLINK_ENABLE_AUTO_FALLBACK,
+		.flags = GENL_ADMIN_PERM,
+		.doit = smc_nl_enable_auto_fallback,
+	},
+	{
+		.cmd = SMC_NETLINK_DISABLE_AUTO_FALLBACK,
+		.flags = GENL_ADMIN_PERM,
+		.doit = smc_nl_disable_auto_fallback,
+	},
 };
 
 static const struct nla_policy smc_gen_nl_policy[2] = {

diff --git a/net/smc/smc_pnet.c b/net/smc/smc_pnet.c
index 291f148..07d7ee8 100644
--- a/net/smc/smc_pnet.c
+++ b/net/smc/smc_pnet.c

@@ -868,6 +868,9 @@ int smc_pnet_net_init(struct net *net)
 
 	smc_pnet_create_pnetids_list(net);
 
+	/* disable auto fallback by default */
+	net->smc.auto_fallback = 0;
+
 	return 0;
 }
 

-- 
1.8.3.1

From: "D. Wythe" <alibuda@linux.alibaba.com>

This patch aims to add dynamic control for SMC auto fallback, since we
don't have socket option level for SMC yet, which requires we need to
implement it at the same time.

This patch does the following:

- add new socket option level: SOL_SMC.
- add new SMC socket option: SMC_AUTO_FALLBACK.
- provide getter/setter for SMC socket options.

Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
---
 include/linux/socket.h   |  1 +
 include/uapi/linux/smc.h |  4 +++
 net/smc/af_smc.c         | 69 +++++++++++++++++++++++++++++++++++++++++++++++-
 net/smc/smc.h            |  1 +
 4 files changed, 74 insertions(+), 1 deletion(-)

diff --git a/include/linux/socket.h b/include/linux/socket.h
index 8ef26d8..6f85f5d 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h

@@ -366,6 +366,7 @@ struct ucred {
 #define SOL_XDP		283
 #define SOL_MPTCP	284
 #define SOL_MCTP	285
+#define SOL_SMC		286
 
 /* IPX options */
 #define IPX_TYPE	1

diff --git a/include/uapi/linux/smc.h b/include/uapi/linux/smc.h
index 6c2874f..9f2cbf8 100644
--- a/include/uapi/linux/smc.h
+++ b/include/uapi/linux/smc.h

@@ -284,4 +284,8 @@ enum {
 	__SMC_NLA_SEID_TABLE_MAX,
 	SMC_NLA_SEID_TABLE_MAX = __SMC_NLA_SEID_TABLE_MAX - 1
 };
+
+/* SMC socket options */
+#define SMC_AUTO_FALLBACK 1	/* allow auto fallback to TCP */
+
 #endif /* _UAPI_LINUX_SMC_H */

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index 8175f60..c313561 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c

@@ -2325,7 +2325,8 @@ static int smc_listen(struct socket *sock, int backlog)
 
 	inet_csk(smc->clcsock->sk)->icsk_af_ops = &smc->af_ops;
 
-	tcp_sk(smc->clcsock->sk)->smc_in_limited = smc_is_in_limited;
+	if (smc->auto_fallback)
+		tcp_sk(smc->clcsock->sk)->smc_in_limited = smc_is_in_limited;
 
 	rc = kernel_listen(smc->clcsock, backlog);
 	if (rc) {

@@ -2620,6 +2621,67 @@ static int smc_shutdown(struct socket *sock, int how)
 	return rc ? rc : rc1;
 }
 
+static int __smc_getsockopt(struct socket *sock, int level, int optname,
+			    char __user *optval, int __user *optlen)
+{
+	struct smc_sock *smc;
+	int val, len;
+
+	smc = smc_sk(sock->sk);
+
+	if (get_user(len, optlen))
+		return -EFAULT;
+
+	len = min_t(int, len, sizeof(int));
+
+	if (len < 0)
+		return -EINVAL;
+
+	switch (optname) {
+	case SMC_AUTO_FALLBACK:
+		val = smc->auto_fallback;
+		break;
+	default:
+		return -EOPNOTSUPP;
+	}
+
+	if (put_user(len, optlen))
+		return -EFAULT;
+	if (copy_to_user(optval, &val, len))
+		return -EFAULT;
+
+	return 0;
+}
+
+static int __smc_setsockopt(struct socket *sock, int level, int optname,
+			    sockptr_t optval, unsigned int optlen)
+{
+	struct sock *sk = sock->sk;
+	struct smc_sock *smc;
+	int val, rc;
+
+	smc = smc_sk(sk);
+
+	lock_sock(sk);
+	switch (optname) {
+	case SMC_AUTO_FALLBACK:
+		if (optlen < sizeof(int))
+			return -EINVAL;
+		if (copy_from_sockptr(&val, optval, sizeof(int)))
+			return -EFAULT;
+
+		smc->auto_fallback = !!val;
+		rc = 0;
+		break;
+	default:
+		rc = -EOPNOTSUPP;
+		break;
+	}
+	release_sock(sk);
+
+	return rc;
+}
+
 static int smc_setsockopt(struct socket *sock, int level, int optname,
 			  sockptr_t optval, unsigned int optlen)
 {

@@ -2629,6 +2691,8 @@ static int smc_setsockopt(struct socket *sock, int level, int optname,
 
 	if (level == SOL_TCP && optname == TCP_ULP)
 		return -EOPNOTSUPP;
+	else if (level == SOL_SMC)
+		return __smc_setsockopt(sock, level, optname, optval, optlen);
 
 	smc = smc_sk(sk);
 

@@ -2711,6 +2775,9 @@ static int smc_getsockopt(struct socket *sock, int level, int optname,
 	struct smc_sock *smc;
 	int rc;
 
+	if (level == SOL_SMC)
+		return __smc_getsockopt(sock, level, optname, optval, optlen);
+
 	smc = smc_sk(sock->sk);
 	mutex_lock(&smc->clcsock_release_lock);
 	if (!smc->clcsock) {

diff --git a/net/smc/smc.h b/net/smc/smc.h
index 5e5e38d..a0bdf75 100644
--- a/net/smc/smc.h
+++ b/net/smc/smc.h

@@ -249,6 +249,7 @@ struct smc_sock {				/* smc sock container */
 	struct work_struct	smc_listen_work;/* prepare new accept socket */
 	struct list_head	accept_q;	/* sockets to be accepted */
 	spinlock_t		accept_q_lock;	/* protects accept_q */
+	bool			auto_fallback;	/* auto fallabck to tcp */
 	bool			use_fallback;	/* fallback to tcp */
 	int			fallback_rsn;	/* reason for fallback */
 	u32			peer_diagnosis; /* decline reason from peer */

-- 
1.8.3.1

On 09/02/2022 15:11, D. Wythe wrote:

+static struct sock *smc_tcp_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
+					  struct request_sock *req,
+					  struct dst_entry *dst,
+					  struct request_sock *req_unhash,
+					  bool *own_req)
+{
+	struct smc_sock *smc;
+
+	smc = (struct smc_sock *)((uintptr_t)sk->sk_user_data & ~SK_USER_DATA_NOCOPY);

Did you run checkpatch.pl for these patches, for me this and other lines look longer 
than 80 characters.

I don't like the name smc_pendings, its not very specific. 
What about queued_smc_hs?
And for the comment: queued smc handshakes

+	struct inet_connection_sock_af_ops		af_ops;
+	const struct inet_connection_sock_af_ops	*ori_af_ops;
+						/* origin af ops */

origin -> original

 	int			sockopt_defer_accept;
 						/* sockopt TCP_DEFER_ACCEPT
 						 * value

-- 
Karsten

On 09/02/2022 15:11, D. Wythe wrote:

From: "D. Wythe" <alibuda@linux.alibaba.com>

This patch intends to provide a mechanism to allow automatic fallback to

I would like to avoid the wording fallback all over here. The term SMC fallback
is used for SMC connections that are in our socket list, but use TCP because 
something went wrong during handshake.
What you changes result in are TCP-only connections which are not handled by
the SMC module at all. So the comments should use a different naming for that.
What the patch actually does is to disable the SMC experimental TCP header option,
so the client receives no SMC indication and does not proceed with SMC.
Is this correct?

Please also see my comments below.

Better variable name: smc_hs_congested

Use new name here and elsewhere ...

Better function name: smc_hs_congested()

Use new names here, too.

+
 	rc = kernel_listen(smc->clcsock, backlog);
 	if (rc) {
 		smc->clcsock->sk->sk_data_ready = smc->clcsk_data_ready;

On 09/02/2022 15:11, D. Wythe wrote:

From: "D. Wythe" <alibuda@linux.alibaba.com>

This patch aims to add dynamic control for SMC auto fallback, since we

Same here, we need a different wording. Maybe something like 
"SMC handshake limitation".

One idea: SMC_LIMIT_HS ?

New variable name: limit_smc_hs ?

 	bool			use_fallback;	/* fallback to tcp */
 	int			fallback_rsn;	/* reason for fallback */
 	u32			peer_diagnosis; /* decline reason from peer */

-- 
Karsten

On 09/02/2022 15:11, D. Wythe wrote:

From: "D. Wythe" <alibuda@linux.alibaba.com>

Although we can control SMC auto fallback through socket options, which
means that applications who need it must modify their code. It's quite
troublesome for many existing applications. This patch modifies the
global default value of auto fallback through netlink, providing a way
to auto fallback without modifying any code for applications.

And of course also in this patch: no "auto fallback" in comments or as part 
of variable names.

Do you plan to enhance the smc-tools user space part, too?

在 2022/2/10 上午12:02, Karsten Graul 写道:

On 09/02/2022 15:11, D. Wythe wrote:

quoted

+static struct sock *smc_tcp_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
+					  struct request_sock *req,
+					  struct dst_entry *dst,
+					  struct request_sock *req_unhash,
+					  bool *own_req)
+{
+	struct smc_sock *smc;
+
+	smc = (struct smc_sock *)((uintptr_t)sk->sk_user_data & ~SK_USER_DATA_NOCOPY);

Did you run checkpatch.pl for these patches, for me this and other lines look longer
than 80 characters.

The latest checkpacth removes this restriction, so I didn't find this 
problem, I'll fix it right away.

quoted

diff --git a/net/smc/smc.h b/net/smc/smc.h
index 37b2001..5e5e38d 100644
--- a/net/smc/smc.h
+++ b/net/smc/smc.h

@@ -252,6 +252,10 @@ struct smc_sock {				/* smc sock container */
  	bool			use_fallback;	/* fallback to tcp */
  	int			fallback_rsn;	/* reason for fallback */
  	u32			peer_diagnosis; /* decline reason from peer */
+	atomic_t                smc_pendings;   /* pending smc connections */

I don't like the name smc_pendings, its not very specific.
What about queued_smc_hs?
And for the comment: queued smc handshakes

quoted

+	struct inet_connection_sock_af_ops		af_ops;
+	const struct inet_connection_sock_af_ops	*ori_af_ops;
+						/* origin af ops */

origin -> original

quoted

  	int			sockopt_defer_accept;
  						/* sockopt TCP_DEFER_ACCEPT
  						 * value

Copy that. I'll rename it all.

在 2022/2/10 上午12:11, Karsten Graul 写道:

On 09/02/2022 15:11, D. Wythe wrote:

quoted

From: "D. Wythe" <alibuda@linux.alibaba.com>

This patch intends to provide a mechanism to allow automatic fallback to

I would like to avoid the wording fallback all over here. The term SMC fallback
is used for SMC connections that are in our socket list, but use TCP because
something went wrong during handshake.
What you changes result in are TCP-only connections which are not handled by
the SMC module at all. So the comments should use a different naming for that.
What the patch actually does is to disable the SMC experimental TCP header option,
so the client receives no SMC indication and does not proceed with SMC.
Is this correct?

Please also see my comments below.

I agree with you, the wording fallback doesn't fit here. I'll try 
limitation.

quoted

TCP according to the pressure of SMC handshake process. At present,
frequent visits will cause the incoming connections to be backlogged in
SMC handshake queue, raise the connections established time. Which is
quite unacceptable for those applications who base on short lived
connections.

There are two ways to implement this mechanism:

1. Fallback when TCP established.
2. Fallback before TCP established.

In the first way, we need to wait and receive CLC messages that the
client will potentially send, and then actively reply with a decline
message, in a sense, which is also a sort of SMC handshake, affect the
connections established time on its way.

In the second way, the only problem is that we need to inject SMC logic
into TCP when it is about to reply the incoming SYN, since we already do
that, it's seems not a problem anymore. And advantage is obvious, few
additional processes are required to complete the fallback.

This patch use the second way.

Link: https://lore.kernel.org/all/1641301961-59331-1-git-send-email-alibuda@linux.alibaba.com/
Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
---
  include/linux/tcp.h  |  1 +
  net/ipv4/tcp_input.c |  3 ++-
  net/smc/af_smc.c     | 18 ++++++++++++++++++
  3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 78b91bb..1c4ae5d 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h

@@ -394,6 +394,7 @@ struct tcp_sock {
  	bool	is_mptcp;
  #endif
  #if IS_ENABLED(CONFIG_SMC)
+	bool	(*smc_in_limited)(const struct sock *sk);

Better variable name: smc_hs_congested

quoted

  	bool	syn_smc;	/* SYN includes SMC */
  #endif
  

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index af94a6d..e817ec6 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c

@@ -6703,7 +6703,8 @@ static void tcp_openreq_init(struct request_sock *req,
  	ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
  	ireq->ir_mark = inet_request_mark(sk, skb);
  #if IS_ENABLED(CONFIG_SMC)
-	ireq->smc_ok = rx_opt->smc_ok;
+	ireq->smc_ok = rx_opt->smc_ok && !(tcp_sk(sk)->smc_in_limited &&
+			tcp_sk(sk)->smc_in_limited(sk));

Use new name here and elsewhere ...

quoted

  #endif
  }
  

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index ebfce3d..8175f60 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c

@@ -101,6 +101,22 @@ static struct sock *smc_tcp_syn_recv_sock(const struct sock *sk, struct sk_buff
  	return NULL;
  }
  
+static bool smc_is_in_limited(const struct sock *sk)

Better function name: smc_hs_congested()

quoted

+{
+	const struct smc_sock *smc;
+
+	smc = (const struct smc_sock *)
+		((uintptr_t)sk->sk_user_data & ~SK_USER_DATA_NOCOPY);
+
+	if (!smc)
+		return true;
+
+	if (workqueue_congested(WORK_CPU_UNBOUND, smc_hs_wq))
+		return true;
+
+	return false;
+}
+
  static struct smc_hashinfo smc_v4_hashinfo = {
  	.lock = __RW_LOCK_UNLOCKED(smc_v4_hashinfo.lock),
  };

@@ -2309,6 +2325,8 @@ static int smc_listen(struct socket *sock, int backlog)
  
  	inet_csk(smc->clcsock->sk)->icsk_af_ops = &smc->af_ops;
  
+	tcp_sk(smc->clcsock->sk)->smc_in_limited = smc_is_in_limited;

Use new names here, too.

quoted

+
  	rc = kernel_listen(smc->clcsock, backlog);
  	if (rc) {
  		smc->clcsock->sk->sk_data_ready = smc->clcsk_data_ready;

Copy that, i'll rename it all soon.

Thanks.

在 2022/2/10 上午12:21, Karsten Graul 写道:

On 09/02/2022 15:11, D. Wythe wrote:

quoted

From: "D. Wythe" <alibuda@linux.alibaba.com>

Although we can control SMC auto fallback through socket options, which
means that applications who need it must modify their code. It's quite
troublesome for many existing applications. This patch modifies the
global default value of auto fallback through netlink, providing a way
to auto fallback without modifying any code for applications.

And of course also in this patch: no "auto fallback" in comments or as part
of variable names.

I will fix all the wording and the naming issues in next series as soon 
as possible.

Do you plan to enhance the smc-tools user space part, too?

Yes, I'll enhance the smc-tools later.

Thanks.