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tcp: add hrtimer slack to sack compression

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Add a sysctl to control hrtimer slack, default of 100 usec.

This gives the opportunity to reduce system overhead,
and help very short RTT flows.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2020-04-30 10:35:43 -07:00 committed by David S. Miller
parent ccd0628fca
commit a70437cc09
5 changed files with 20 additions and 2 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

8
Documentation/networking/ip-sysctl.rst
View file

@ -651,6 +651,14 @@ tcp_comp_sack_delay_ns - LONG INTEGER
Default : 1,000,000 ns (1 ms)
tcp_comp_sack_slack_ns - LONG INTEGER
This sysctl control the slack used when arming the
timer used by SACK compression. This gives extra time
for small RTT flows, and reduces system overhead by allowing
opportunistic reduction of timer interrupts.
Default : 100,000 ns (100 us)
tcp_comp_sack_nr - INTEGER
Max number of SACK that can be compressed.
Using 0 disables SACK compression.

1
include/net/netns/ipv4.h
View file

@ -173,6 +173,7 @@ struct netns_ipv4 {
int sysctl_tcp_rmem[3];
int sysctl_tcp_comp_sack_nr;
unsigned long sysctl_tcp_comp_sack_delay_ns;
unsigned long sysctl_tcp_comp_sack_slack_ns;
struct inet_timewait_death_row tcp_death_row;
int sysctl_max_syn_backlog;
int sysctl_tcp_fastopen;

7
net/ipv4/sysctl_net_ipv4.c
View file

@ -1329,6 +1329,13 @@ static struct ctl_table ipv4_net_table[] = {
.mode = 0644,
.proc_handler = proc_doulongvec_minmax,
},
{
.procname = "tcp_comp_sack_slack_ns",
.data = &init_net.ipv4.sysctl_tcp_comp_sack_slack_ns,
.maxlen = sizeof(unsigned long),
.mode = 0644,
.proc_handler = proc_doulongvec_minmax,
},
{
.procname = "tcp_comp_sack_nr",
.data = &init_net.ipv4.sysctl_tcp_comp_sack_nr,

3
net/ipv4/tcp_input.c
View file

@ -5324,7 +5324,8 @@ static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
delay = min_t(unsigned long, sock_net(sk)->ipv4.sysctl_tcp_comp_sack_delay_ns,
rtt * (NSEC_PER_USEC >> 3)/20);
sock_hold(sk);
hrtimer_start(&tp->compressed_ack_timer, ns_to_ktime(delay),
hrtimer_start_range_ns(&tp->compressed_ack_timer, ns_to_ktime(delay),
sock_net(sk)->ipv4.sysctl_tcp_comp_sack_slack_ns,
HRTIMER_MODE_REL_PINNED_SOFT);
}

1
net/ipv4/tcp_ipv4.c
View file

@ -2780,6 +2780,7 @@ static int __net_init tcp_sk_init(struct net *net)
sizeof(init_net.ipv4.sysctl_tcp_wmem));
}
net->ipv4.sysctl_tcp_comp_sack_delay_ns = NSEC_PER_MSEC;
net->ipv4.sysctl_tcp_comp_sack_slack_ns = 100 * NSEC_PER_USEC;
net->ipv4.sysctl_tcp_comp_sack_nr = 44;
net->ipv4.sysctl_tcp_fastopen = TFO_CLIENT_ENABLE;
spin_lock_init(&net->ipv4.tcp_fastopen_ctx_lock);