diff mbox series

[net-next,v4,3/3] net/smc: Fallback when handshake workqueue congested

Message ID 6deeca64bfecbd01d724092a1a2c91ca8bce3ce0.1644214112.git.alibuda@linux.alibaba.com (mailing list archive)
State Superseded
Headers show
Series net/smc: Optimizing performance in short-lived scenarios | expand

Commit Message

D. Wythe Feb. 7, 2022, 6:24 a.m. UTC 
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.

It should be optional for applications that don't care about connection
established time. For now, this patch only provides the switch at the
compile time.

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/Kconfig      | 12 ++++++++++++
 net/smc/af_smc.c     | 22 ++++++++++++++++++++++
 4 files changed, 37 insertions(+), 1 deletion(-)

Comments

Karsten Graul Feb. 7, 2022, 7:56 a.m. UTC | #1 
On 07/02/2022 07:24, D. Wythe wrote:
> 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.

I hope I didn't miss any news, but with your latest reply to the v2 series you
questioned the config option in this v4 patch, so this is still work in progress, right?
D. Wythe Feb. 7, 2022, 9:50 a.m. UTC | #2 
The main communication in v2 series is about adding a dynamic control 
for auto fallback to TCP. I will soon add a new patch to implements this 
in v5 series, or modify it in curret patch. Which one do you recommend?

Look forward to your suggestions.

Thanks.


在 2022/2/7 下午3:56, Karsten Graul 写道:
> On 07/02/2022 07:24, D. Wythe wrote:
>> 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.
> 
> I hope I didn't miss any news, but with your latest reply to the v2 series you
> questioned the config option in this v4 patch, so this is still work in progress, right?
Karsten Graul Feb. 7, 2022, 10:03 a.m. UTC | #3 
On 07/02/2022 10:50, D. Wythe wrote:
> 
> The main communication in v2 series is about adding a dynamic control for auto fallback to TCP. I will soon add a new patch to implements this in v5 series, or modify it in curret patch. Which one do you recommend?
> 

When you change a patch then you need to send a new series.
D. Wythe Feb. 8, 2022, 12:58 p.m. UTC | #4 
You may have misunderstood what I mean ... but it doesn't matter now, 
I've sent the v5 series.

Looking forward to your suggestions for v5 series.

Thanks.

在 2022/2/7 下午6:03, Karsten Graul 写道:
> On 07/02/2022 10:50, D. Wythe wrote:
>>
>> The main communication in v2 series is about adding a dynamic control for auto fallback to TCP. I will soon add a new patch to implements this in v5 series, or modify it in curret patch. Which one do you recommend?
>>
> 
> When you change a patch then you need to send a new series.
diff mbox series

Patch

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 dc49a3d..9890de9 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6701,7 +6701,8 @@  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/Kconfig b/net/smc/Kconfig
index 1ab3c5a..a4e1713 100644
--- a/net/smc/Kconfig
+++ b/net/smc/Kconfig
@@ -19,3 +19,15 @@  config SMC_DIAG
 	  smcss.
 
 	  if unsure, say Y.
+
+if SMC
+
+config SMC_AUTO_FALLBACK
+	bool "SMC: automatic fallback to TCP"
+	default y
+	help
+	  Allow automatic fallback to TCP accroding to the pressure of SMC-R
+	  handshake process.
+
+	  If that's not what you except or unsure, say N.
+endif
diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index 697573f..46f86a2 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -101,6 +101,24 @@  static struct sock *smc_tcp_syn_recv_sock(const struct sock *sk, struct sk_buff
 	return NULL;
 }
 
+#if IS_ENABLED(CONFIG_SMC_AUTO_FALLBACK)
+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;
+}
+#endif
+
 static struct smc_hashinfo smc_v4_hashinfo = {
 	.lock = __RW_LOCK_UNLOCKED(smc_v4_hashinfo.lock),
 };
@@ -2206,6 +2224,10 @@  static int smc_listen(struct socket *sock, int backlog)
 
 	inet_csk(smc->clcsock->sk)->icsk_af_ops = &smc->af_ops;
 
+#if IS_ENABLED(CONFIG_SMC_AUTO_FALLBACK)
+	tcp_sk(smc->clcsock->sk)->smc_in_limited = smc_is_in_limited;
+#endif
+
 	rc = kernel_listen(smc->clcsock, backlog);
 	if (rc) {
 		smc->clcsock->sk->sk_data_ready = smc->clcsk_data_ready;