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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 • committed by John Stultz
commit 72fc8653dc
4 changed files with 25 additions and 1 deletions
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1
include/net/tcp.h
View file

@ -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;

22
net/ipv4/sysctl_net_ipv4.c
View file

@ -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,

1
net/ipv4/tcp_input.c
View file

@ -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. */

2
net/ipv4/tcp_output.c
View file

@ -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);