tcp: add a sysctl to config the tcp_default_init_rwnd

The default initial rwnd is hardcoded to 10.

Now we allow it to be controlled via
  /proc/sys/net/ipv4/tcp_default_init_rwnd
which limits the values from 3 to 100

This is somewhat needed because ipv6 routes are
autoconfigured by the kernel.

See "An Argument for Increasing TCP's Initial Congestion Window"
in https://developers.google.com/speed/articles/tcp_initcwnd_paper.pdf

Change-Id: I386b2a9d62de0ebe05c1ebe1b4bd91b314af5c54
Signed-off-by: JP Abgrall <jpa@google.com>
Conflicts:
	net/ipv4/sysctl_net_ipv4.c
	net/ipv4/tcp_input.c

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 0020825157e20b86557c97705852c7e48139b397..b64bdeea00a993c7ec0de880309e9437adc27f5f 100644 (file)
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -284,6 +284,7 @@ extern int sysctl_tcp_autocorking;
 extern int sysctl_tcp_invalid_ratelimit;
 extern int sysctl_tcp_pacing_ss_ratio;
 extern int sysctl_tcp_pacing_ca_ratio;
+extern int sysctl_tcp_default_init_rwnd;
 
 extern atomic_long_t tcp_memory_allocated;
 extern struct percpu_counter tcp_sockets_allocated;

diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index a0bd7a55193e351c9ec75a469315c44e76195fd1..dd825be50089d91446d861eec56e7974cccab8c4 100644 (file)
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -152,6 +152,21 @@ static int ipv4_ping_group_range(struct ctl_table *table, int write,
        return ret;
 }
 
+/* Validate changes from /proc interface. */
+static int proc_tcp_default_init_rwnd(ctl_table *ctl, int write,
+                                     void __user *buffer,
+                                     size_t *lenp, loff_t *ppos)
+{
+       int old_value = *(int *)ctl->data;
+       int ret = proc_dointvec(ctl, write, buffer, lenp, ppos);
+       int new_value = *(int *)ctl->data;
+
+       if (write && ret == 0 && (new_value < 3 || new_value > 100))
+               *(int *)ctl->data = old_value;
+
+       return ret;
+}
+
 static int proc_tcp_congestion_control(struct ctl_table *ctl, int write,
                                       void __user *buffer, size_t *lenp, loff_t *ppos)
 {
@@ -760,6 +775,13 @@ static struct ctl_table ipv4_table[] = {
                .mode           = 0644,
                .proc_handler   = proc_dointvec_ms_jiffies,
        },
+       {
+               .procname       = "tcp_default_init_rwnd",
+               .data           = &sysctl_tcp_default_init_rwnd,
+               .maxlen         = sizeof(int),
+               .mode           = 0644,
+               .proc_handler   = proc_tcp_default_init_rwnd
+       },
        {
                .procname       = "icmp_msgs_per_sec",
                .data           = &sysctl_icmp_msgs_per_sec,

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index d4c51158470f5afb7cee8a5c875b5f9ed5b04e14..da34f830f4bc17ba611a6151d4feebc4ae5faa72 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -102,6 +102,7 @@ int sysctl_tcp_thin_dupack __read_mostly;
 int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
 int sysctl_tcp_early_retrans __read_mostly = 3;
 int sysctl_tcp_invalid_ratelimit __read_mostly = HZ/2;
+int sysctl_tcp_default_init_rwnd __read_mostly = TCP_INIT_CWND * 2;
 
 #define FLAG_DATA              0x01 /* Incoming frame contained data.          */
 #define FLAG_WIN_UPDATE                0x02 /* Incoming ACK was a window update.       */

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 9bfc39ff2285aecaab86f519a017b84282cb6597..9f069bd9de468c8add79da5762474a90c4b74d5b 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -191,7 +191,7 @@ u32 tcp_default_init_rwnd(u32 mss)
         * (RFC 3517, Section 4, NextSeg() rule (2)). Further place a
         * limit when mss is larger than 1460.
         */
-       u32 init_rwnd = TCP_INIT_CWND * 2;
+       u32 init_rwnd = sysctl_tcp_default_init_rwnd;
 
        if (mss > 1460)
                init_rwnd = max((1460 * init_rwnd) / mss, 2U);