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tcp: track total bytes delivered with ECN CE marks

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Introduce a new delivered_ce stat in tcp socket to estimate
number of packets being marked with CE bits. The estimation is
done via ACKs with ECE bit. Depending on the actual receiver
behavior, the estimation could have biases.

Since the TCP sender can't really see the CE bit in the data path,
so the sender is technically counting packets marked delivered with
the "ECE / ECN-Echo" flag set.

With RFC3168 ECN, because the ECE bit is sticky, this count can
drastically overestimate the nummber of CE-marked data packets

With DCTCP-style ECN this should be reasonably precise unless there
is loss in the ACK path, in which case it's not precise.

With AccECN proposal this can be made still more precise, even in
the case some degree of ACK loss.

However this is sender's best estimate of CE information.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Reviewed-by: Neal Cardwell <ncardwell@google.com>
Reviewed-by: Soheil Hassas Yeganeh <soheil@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Yuchung Cheng 2018-04-17 23:18:48 -07:00 committed by David S. Miller
parent a77fa0104a
commit e21db6f69a
3 changed files with 4 additions and 0 deletions
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1
include/linux/tcp.h
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@ -281,6 +281,7 @@ struct tcp_sock {
* receiver in Recovery. */
u32 prr_out; /* Total number of pkts sent during Recovery. */
u32 delivered; /* Total data packets delivered incl. rexmits */
u32 delivered_ce; /* Like the above but only ECE marked packets */
u32 lost; /* Total data packets lost incl. rexmits */
u32 app_limited; /* limited until "delivered" reaches this val */
u64 first_tx_mstamp; /* start of window send phase */

1
net/ipv4/tcp.c
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@ -2559,6 +2559,7 @@ int tcp_disconnect(struct sock *sk, int flags)
tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
tp->snd_cwnd_cnt = 0;
tp->window_clamp = 0;
tp->delivered_ce = 0;
tcp_set_ca_state(sk, TCP_CA_Open);
tp->is_sack_reneg = 0;
tcp_clear_retrans(tp);

2
net/ipv4/tcp_input.c
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@ -3503,6 +3503,8 @@ static u32 tcp_newly_delivered(struct sock *sk, u32 prior_delivered, int flag)
u32 delivered;
delivered = tp->delivered - prior_delivered;
if (flag & FLAG_ECE)
tp->delivered_ce += delivered;
return delivered;
}