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tcp: fix tcp_disordered_ack() vs usec TS resolution

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After commit 939463016b7a ("tcp: change data receiver flowlabel after one dup")
we noticed an increase of TCPACKSkippedPAWS events.

Neal Cardwell tracked the issue to tcp_disordered_ack() assumption
about remote peer TS clock.

RFC 1323 & 7323 are suggesting the following:
  "timestamp clock frequency in the range 1 ms to 1 sec per tick
   between 1ms and 1sec."

This has to be adjusted for 1 MHz clock frequency.

This hints at reorders of SACK packets on send side,
this might deserve a future patch.
(skb->ooo_okay is always set for pure ACK packets)

Fixes: 614e8316aa4c ("tcp: add support for usec resolution in TCP TS values")
Co-developed-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: David Morley <morleyd@google.com>
Link: https://lore.kernel.org/r/20231207181342.525181-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet 2023-12-07 18:13:42 +00:00 committed by Jakub Kicinski
parent a45f1e4627
commit 9c25aae013
1 changed files with 20 additions and 2 deletions
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22
net/ipv4/tcp_input.c
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@ -4368,6 +4368,23 @@ EXPORT_SYMBOL(tcp_do_parse_auth_options);
* up to bandwidth of 18Gigabit/sec. 8) ]
*/
/* Estimates max number of increments of remote peer TSval in
* a replay window (based on our current RTO estimation).
*/
static u32 tcp_tsval_replay(const struct sock *sk)
{
/* If we use usec TS resolution,
* then expect the remote peer to use the same resolution.
*/
if (tcp_sk(sk)->tcp_usec_ts)
return inet_csk(sk)->icsk_rto * (USEC_PER_SEC / HZ);
/* RFC 7323 recommends a TSval clock between 1ms and 1sec.
* We know that some OS (including old linux) can use 1200 Hz.
*/
return inet_csk(sk)->icsk_rto * 1200 / HZ;
}
static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
{
const struct tcp_sock *tp = tcp_sk(sk);
@ -4375,7 +4392,7 @@ static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
u32 seq = TCP_SKB_CB(skb)->seq;
u32 ack = TCP_SKB_CB(skb)->ack_seq;
return (/* 1. Pure ACK with correct sequence number. */
return /* 1. Pure ACK with correct sequence number. */
(th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
/* 2. ... and duplicate ACK. */
@ -4385,7 +4402,8 @@ static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
!tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
/* 4. ... and sits in replay window. */
(s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
(s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <=
tcp_tsval_replay(sk);
}
static inline bool tcp_paws_discard(const struct sock *sk,