net/smc: add sysctl for autocorking

This add a new sysctl: net.smc.autocorking_size

We can dynamically change the behaviour of autocorking
by change the value of autocorking_size.
Setting to 0 disables autocorking in SMC
Signed-off-by: Dust Li <dust.li@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/smc-sysctl.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+=========
+SMC Sysctl
+=========
+
+/proc/sys/net/smc/* Variables
+==============================
+
+autocorking_size - INTEGER
+	Setting SMC auto corking size:
+	SMC auto corking is like TCP auto corking from the application's
+	perspective of view. When applications do consecutive small
+	write()/sendmsg() system calls, we try to coalesce these small writes
+	as much as possible, to lower total amount of CDC and RDMA Write been
+	sent.
+	autocorking_size limits the maximum corked bytes that can be sent to
+	the under device in 1 single sending. If set to 0, the SMC auto corking
+	is disabled.
+	Applications can still use TCP_CORK for optimal behavior when they
+	know how/when to uncork their sockets.
+
+	Default: 64K

include/net/netns/smc.h

@@ -17,5 +17,6 @@ struct netns_smc {
 #ifdef CONFIG_SYSCTL
 	struct ctl_table_header		*smc_hdr;
 #endif
+	unsigned int			sysctl_autocorking_size;
 };
 #endif

net/smc/smc_sysctl.c

@@ -14,9 +14,17 @@
 #include <linux/sysctl.h>
 #include <net/net_namespace.h>
 
+#include "smc.h"
 #include "smc_sysctl.h"
 
 static struct ctl_table smc_table[] = {
+	{
+		.procname       = "autocorking_size",
+		.data           = &init_net.smc.sysctl_autocorking_size,
+		.maxlen         = sizeof(unsigned int),
+		.mode           = 0644,
+		.proc_handler	= proc_douintvec,
+	},
 	{  }
 };
 
@@ -40,6 +48,8 @@ static __net_init int smc_sysctl_init_net(struct net *net)
 	if (!net->smc.smc_hdr)
 		goto err_reg;
 
+	net->smc.sysctl_autocorking_size = SMC_AUTOCORKING_DEFAULT_SIZE;
+
 	return 0;
 
 err_reg:

net/smc/smc_tx.c

@@ -147,7 +147,7 @@ static bool smc_should_autocork(struct smc_sock *smc)
 	struct smc_connection *conn = &smc->conn;
 	int corking_size;
 
-	corking_size = min(SMC_AUTOCORKING_DEFAULT_SIZE,
+	corking_size = min(sock_net(&smc->sk)->smc.sysctl_autocorking_size,
 			   conn->sndbuf_desc->len >> 1);
 
 	if (atomic_read(&conn->cdc_pend_tx_wr) == 0 ||