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 1ed71a9..cfb55e1 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -287,6 +287,7 @@
extern int sysctl_tcp_early_retrans;
extern int sysctl_tcp_limit_output_bytes;
extern int sysctl_tcp_challenge_ack_limit;
+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 fa2f63f..f9bb5d7 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -135,6 +135,21 @@
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(ctl_table *ctl, int write,
void __user *buffer, size_t *lenp, loff_t *ppos)
{
@@ -732,7 +747,7 @@
.mode = 0644,
.proc_handler = proc_dointvec
},
- {
+ {
.procname = "tcp_thin_dupack",
.data = &sysctl_tcp_thin_dupack,
.maxlen = sizeof(int),
@@ -749,6 +764,13 @@
.extra2 = &four,
},
{
+ .procname = "tcp_default_init_rwnd",
+ .data = &sysctl_tcp_default_init_rwnd,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_tcp_default_init_rwnd
+ },
+ {
.procname = "udp_mem",
.data = &sysctl_udp_mem,
.maxlen = sizeof(sysctl_udp_mem),
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 9c62257..4189682 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -98,6 +98,7 @@
int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
int sysctl_tcp_early_retrans __read_mostly = 3;
+int sysctl_tcp_default_init_rwnd __read_mostly = TCP_DEFAULT_INIT_RCVWND;
#define FLAG_DATA 0x01 /* Incoming frame contained data. */
#define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window update. */
@@ -351,14 +352,14 @@
static void tcp_fixup_rcvbuf(struct sock *sk)
{
u32 mss = tcp_sk(sk)->advmss;
- u32 icwnd = TCP_DEFAULT_INIT_RCVWND;
+ u32 icwnd = sysctl_tcp_default_init_rwnd;
int rcvmem;
/* Limit to 10 segments if mss <= 1460,
* or 14600/mss segments, with a minimum of two segments.
*/
if (mss > 1460)
- icwnd = max_t(u32, (1460 * TCP_DEFAULT_INIT_RCVWND) / mss, 2);
+ icwnd = max_t(u32, (1460 * icwnd) / mss, 2);
rcvmem = SKB_TRUESIZE(mss + MAX_TCP_HEADER);
while (tcp_win_from_space(rcvmem) < mss)
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index ec335fa..084eac6 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -231,14 +231,13 @@
}
/* Set initial window to a value enough for senders starting with
- * initial congestion window of TCP_DEFAULT_INIT_RCVWND. Place
+ * initial congestion window of sysctl_tcp_default_init_rwnd. Place
* a limit on the initial window when mss is larger than 1460.
*/
if (mss > (1 << *rcv_wscale)) {
- int init_cwnd = TCP_DEFAULT_INIT_RCVWND;
+ int init_cwnd = sysctl_tcp_default_init_rwnd;
if (mss > 1460)
- init_cwnd =
- max_t(u32, (1460 * TCP_DEFAULT_INIT_RCVWND) / mss, 2);
+ init_cwnd = max_t(u32, (1460 * init_cwnd) / mss, 2);
/* when initializing use the value from init_rcv_wnd
* rather than the default from above
*/