tcp: switch TCP TS option (RFC 7323) to 1ms clock
TCP Timestamps option is defined in RFC 7323
Traditionally on linux, it has been tied to the internal
'jiffies' variable, because it had been a cheap and good enough
generator.
For TCP flows on the Internet, 1 ms resolution would be much better
than 4ms or 10ms (HZ=250 or HZ=100 respectively)
For TCP flows in the DC, Google has used usec resolution for more
than two years with great success [1]
Receive size autotuning (DRS) is indeed more precise and converges
faster to optimal window size.
This patch converts tp->tcp_mstamp to a plain u64 value storing
a 1 usec TCP clock.
This choice will allow us to upstream the 1 usec TS option as
discussed in IETF 97.
[1] https://www.ietf.org/proceedings/97/slides/slides-97-tcpm-tcp-options-for-low-latency-00.pdf
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index d8fe25d..191b2f7 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -376,8 +376,9 @@
struct sock *sk;
struct sk_buff *skb;
struct request_sock *fastopen;
- __u32 seq, snd_una;
- __u32 remaining;
+ u32 seq, snd_una;
+ s32 remaining;
+ u32 delta_us;
int err;
struct net *net = dev_net(icmp_skb->dev);
@@ -483,12 +484,12 @@
skb = tcp_write_queue_head(sk);
BUG_ON(!skb);
- skb_mstamp_get(&tp->tcp_mstamp);
+ tcp_mstamp_refresh(tp);
+ delta_us = (u32)(tp->tcp_mstamp - skb->skb_mstamp);
remaining = icsk->icsk_rto -
- min(icsk->icsk_rto,
- tcp_time_stamp - tcp_skb_timestamp(skb));
+ usecs_to_jiffies(delta_us);
- if (remaining) {
+ if (remaining > 0) {
inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
remaining, TCP_RTO_MAX);
} else {
@@ -812,7 +813,7 @@
tcp_v4_send_ack(sk, skb,
tcptw->tw_snd_nxt, tcptw->tw_rcv_nxt,
tcptw->tw_rcv_wnd >> tw->tw_rcv_wscale,
- tcp_time_stamp + tcptw->tw_ts_offset,
+ tcp_time_stamp_raw() + tcptw->tw_ts_offset,
tcptw->tw_ts_recent,
tw->tw_bound_dev_if,
tcp_twsk_md5_key(tcptw),
@@ -840,7 +841,7 @@
tcp_v4_send_ack(sk, skb, seq,
tcp_rsk(req)->rcv_nxt,
req->rsk_rcv_wnd >> inet_rsk(req)->rcv_wscale,
- tcp_time_stamp + tcp_rsk(req)->ts_off,
+ tcp_time_stamp_raw() + tcp_rsk(req)->ts_off,
req->ts_recent,
0,
tcp_md5_do_lookup(sk, (union tcp_md5_addr *)&ip_hdr(skb)->daddr,