Per RFC4898, they count segments sent/received
containing a positive length data segment (that includes
retransmission segments carrying data).  Unlike
tcpi_segs_out/in, tcpi_data_segs_out/in excludes segments
carrying no data (e.g. pure ack).

The patch also updates the segs_in in tcp_fastopen_add_skb()
so that segs_in >= data_segs_in property is kept.

Together with retransmission data, tcpi_data_segs_out
gives a better signal on the rxmit rate.

Signed-off-by: Martin KaFai Lau <ka...@fb.com>
Cc: Chris Rapier <rap...@psc.edu>
Cc: Eric Dumazet <eduma...@google.com>
Cc: Marcelo Ricardo Leitner <mleit...@redhat.com>
Cc: Neal Cardwell <ncardw...@google.com>
Cc: Yuchung Cheng <ych...@google.com>
---
 include/linux/tcp.h      | 6 ++++++
 include/uapi/linux/tcp.h | 2 ++
 net/ipv4/tcp.c           | 2 ++
 net/ipv4/tcp_fastopen.c  | 4 ++++
 net/ipv4/tcp_ipv4.c      | 7 ++++++-
 net/ipv4/tcp_output.c    | 4 +++-
 net/ipv6/tcp_ipv6.c      | 7 ++++++-
 7 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index bcbf51d..7be9b12 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -158,6 +158,9 @@ struct tcp_sock {
        u32     segs_in;        /* RFC4898 tcpEStatsPerfSegsIn
                                 * total number of segments in.
                                 */
+       u32     data_segs_in;   /* RFC4898 tcpEStatsPerfDataSegsIn
+                                * total number of data segments in.
+                                */
        u32     rcv_nxt;        /* What we want to receive next         */
        u32     copied_seq;     /* Head of yet unread data              */
        u32     rcv_wup;        /* rcv_nxt on last window update sent   */
@@ -165,6 +168,9 @@ struct tcp_sock {
        u32     segs_out;       /* RFC4898 tcpEStatsPerfSegsOut
                                 * The total number of segments sent.
                                 */
+       u32     data_segs_out;  /* RFC4898 tcpEStatsPerfDataSegsOut
+                                * total number of data segments sent.
+                                */
        u64     bytes_acked;    /* RFC4898 tcpEStatsAppHCThruOctetsAcked
                                 * sum(delta(snd_una)), or how many bytes
                                 * were acked.
diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h
index fe95446..53e8e3f 100644
--- a/include/uapi/linux/tcp.h
+++ b/include/uapi/linux/tcp.h
@@ -199,6 +199,8 @@ struct tcp_info {
 
        __u32   tcpi_notsent_bytes;
        __u32   tcpi_min_rtt;
+       __u32   tcpi_data_segs_in;      /* RFC4898 tcpEStatsDataSegsIn */
+       __u32   tcpi_data_segs_out;     /* RFC4898 tcpEStatsDataSegsOut */
 };
 
 /* for TCP_MD5SIG socket option */
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index f9faadb..6b01b48 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2728,6 +2728,8 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
        info->tcpi_notsent_bytes = max(0, notsent_bytes);
 
        info->tcpi_min_rtt = tcp_min_rtt(tp);
+       info->tcpi_data_segs_in = tp->data_segs_in;
+       info->tcpi_data_segs_out = tp->data_segs_out;
 }
 EXPORT_SYMBOL_GPL(tcp_get_info);
 
diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index fdb286d..f583c85 100644
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -131,6 +131,7 @@ static bool tcp_fastopen_cookie_gen(struct request_sock 
*req,
 void tcp_fastopen_add_skb(struct sock *sk, struct sk_buff *skb)
 {
        struct tcp_sock *tp = tcp_sk(sk);
+       u16 segs_in;
 
        if (TCP_SKB_CB(skb)->end_seq == tp->rcv_nxt)
                return;
@@ -154,6 +155,9 @@ void tcp_fastopen_add_skb(struct sock *sk, struct sk_buff 
*skb)
         * as we certainly are not changing upper 32bit value (0)
         */
        tp->bytes_received = skb->len;
+       segs_in = max_t(u16, 1, skb_shinfo(skb)->gso_segs);
+       tp->segs_in = segs_in;
+       tp->data_segs_in = segs_in;
 
        if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
                tcp_fin(sk);
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 4c8d58d..c9b576f 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1540,6 +1540,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
        const struct iphdr *iph;
        const struct tcphdr *th;
        struct sock *sk;
+       u16 segs_in;
        int ret;
        struct net *net = dev_net(skb->dev);
 
@@ -1650,7 +1651,11 @@ process:
        sk_incoming_cpu_update(sk);
 
        bh_lock_sock_nested(sk);
-       tcp_sk(sk)->segs_in += max_t(u16, 1, skb_shinfo(skb)->gso_segs);
+       segs_in = max_t(u16, 1, skb_shinfo(skb)->gso_segs);
+       tcp_sk(sk)->segs_in += segs_in;
+       if (skb->len > __tcp_hdrlen(th))
+               tcp_sk(sk)->data_segs_in += segs_in;
+
        ret = 0;
        if (!sock_owned_by_user(sk)) {
                if (!tcp_prequeue(sk, skb))
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 7d2c7a4..7d2dc01 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1003,8 +1003,10 @@ static int tcp_transmit_skb(struct sock *sk, struct 
sk_buff *skb, int clone_it,
        if (likely(tcb->tcp_flags & TCPHDR_ACK))
                tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
 
-       if (skb->len != tcp_header_size)
+       if (skb->len != tcp_header_size) {
                tcp_event_data_sent(tp, sk);
+               tp->data_segs_out += tcp_skb_pcount(skb);
+       }
 
        if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
                TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 33f2820..941a8a5 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1349,6 +1349,7 @@ static int tcp_v6_rcv(struct sk_buff *skb)
        const struct tcphdr *th;
        const struct ipv6hdr *hdr;
        struct sock *sk;
+       u16 segs_in;
        int ret;
        struct net *net = dev_net(skb->dev);
 
@@ -1443,7 +1444,11 @@ process:
        sk_incoming_cpu_update(sk);
 
        bh_lock_sock_nested(sk);
-       tcp_sk(sk)->segs_in += max_t(u16, 1, skb_shinfo(skb)->gso_segs);
+       segs_in = max_t(u16, 1, skb_shinfo(skb)->gso_segs);
+       tcp_sk(sk)->segs_in += segs_in;
+       if (skb->len > __tcp_hdrlen(th))
+               tcp_sk(sk)->data_segs_in += segs_in;
+
        ret = 0;
        if (!sock_owned_by_user(sk)) {
                if (!tcp_prequeue(sk, skb))
-- 
2.5.1

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