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tcp: switch TCP TS option (RFC 7323) to 1ms clock

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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>
This commit is contained in:
Eric Dumazet
2017-05-16 14:00:14 -07:00
committed by David S. Miller
parent ac9517fcf3
commit 9a568de481
17 changed files with 178 additions and 199 deletions
Download Patch File Download Diff File Expand all files Collapse all files

8
net/ipv4/syncookies.c
View File

@@ -66,10 +66,10 @@ static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport,
* Since subsequent timestamps use the normal tcp_time_stamp value, we
* must make sure that the resulting initial timestamp is <= tcp_time_stamp.
*/
__u32 cookie_init_timestamp(struct request_sock *req)
u64 cookie_init_timestamp(struct request_sock *req)
{
struct inet_request_sock *ireq;
u32 ts, ts_now = tcp_time_stamp;
u32 ts, ts_now = tcp_time_stamp_raw();
u32 options = 0;
ireq = inet_rsk(req);
@@ -88,7 +88,7 @@ __u32 cookie_init_timestamp(struct request_sock *req)
ts <<= TSBITS;
ts |= options;
}
return ts;
return (u64)ts * (USEC_PER_SEC / TCP_TS_HZ);
}
@@ -343,7 +343,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
ireq->wscale_ok = tcp_opt.wscale_ok;
ireq->tstamp_ok = tcp_opt.saw_tstamp;
req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
treq->snt_synack.v64 = 0;
treq->snt_synack = 0;
treq->tfo_listener = false;
ireq->ir_iif = inet_request_bound_dev_if(sk, skb);