Commit e21db6f6 authored Apr 17, 2018 by Yuchung Cheng Committed by David S. Miller Apr 19, 2018

tcp: track total bytes delivered with ECN CE marks



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>

parent a77fa010

include/linux/tcp.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -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 */

net/ipv4/tcp.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -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);

net/ipv4/tcp_input.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -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;
		}

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