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tcp: add a sysctl to config the tcp_default_init_rwnd

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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
This commit is contained in:
JP Abgrall 2014-02-07 18:40:10 -08:00
parent 43fcab022e
commit 969ff3bbb3
4 changed files with 30 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/net/tcp.h
View File

@ -287,6 +287,7 @@ extern int sysctl_tcp_thin_dupack;
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;

24
net/ipv4/sysctl_net_ipv4.c
View File

@ -135,6 +135,21 @@ static int ipv4_ping_group_range(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(ctl_table *ctl, int write,
void __user *buffer, size_t *lenp, loff_t *ppos)
{
@ -732,7 +747,7 @@ static struct ctl_table ipv4_table[] = {
.mode = 0644,
.proc_handler = proc_dointvec
},
{
{
.procname = "tcp_thin_dupack",
.data = &sysctl_tcp_thin_dupack,
.maxlen = sizeof(int),
@ -748,6 +763,13 @@ static struct ctl_table ipv4_table[] = {
.extra1 = &zero,
.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,

5
net/ipv4/tcp_input.c
View File

@ -98,6 +98,7 @@ 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_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_grow_window(struct sock *sk, const struct sk_buff *skb)
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)

7
net/ipv4/tcp_output.c
View File

@ -231,14 +231,13 @@ void tcp_select_initial_window(int __space, __u32 mss,
}
/* 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
*/