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>

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 8f4c549..20585d5 100644 (file)
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -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 */

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 438fbca..5a5ce6d 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -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);

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 01cce28..b3bff9c 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -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;
 }