tcp: take care of compressed acks in tcp_add_reno_sack()

Neal pointed out that non sack flows might suffer from ACK compression
added in the following patch ("tcp: implement coalescing on backlog queue")

Instead of tweaking tcp_add_backlog() we can take into
account how many ACK were coalesced, this information
will be available in skb_shinfo(skb)->gso_segs

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 7875274..76858b1 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1865,16 +1865,20 @@ static void tcp_check_reno_reordering(struct sock *sk, const int addend)
 
 /* Emulate SACKs for SACKless connection: account for a new dupack. */
 
-static void tcp_add_reno_sack(struct sock *sk)
+static void tcp_add_reno_sack(struct sock *sk, int num_dupack)
 {
-       struct tcp_sock *tp = tcp_sk(sk);
-       u32 prior_sacked = tp->sacked_out;
+       if (num_dupack) {
+               struct tcp_sock *tp = tcp_sk(sk);
+               u32 prior_sacked = tp->sacked_out;
+               s32 delivered;
 
-       tp->sacked_out++;
-       tcp_check_reno_reordering(sk, 0);
-       if (tp->sacked_out > prior_sacked)
-               tp->delivered++; /* Some out-of-order packet is delivered */
-       tcp_verify_left_out(tp);
+               tp->sacked_out += num_dupack;
+               tcp_check_reno_reordering(sk, 0);
+               delivered = tp->sacked_out - prior_sacked;
+               if (delivered > 0)
+                       tp->delivered += delivered;
+               tcp_verify_left_out(tp);
+       }
 }
 
 /* Account for ACK, ACKing some data in Reno Recovery phase. */
@@ -2636,7 +2640,7 @@ void tcp_enter_recovery(struct sock *sk, bool ece_ack)
 /* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
  * recovered or spurious. Otherwise retransmits more on partial ACKs.
  */
-static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack,
+static void tcp_process_loss(struct sock *sk, int flag, int num_dupack,
                             int *rexmit)
 {
        struct tcp_sock *tp = tcp_sk(sk);
@@ -2655,7 +2659,7 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack,
                        return;
 
                if (after(tp->snd_nxt, tp->high_seq)) {
-                       if (flag & FLAG_DATA_SACKED || is_dupack)
+                       if (flag & FLAG_DATA_SACKED || num_dupack)
                                tp->frto = 0; /* Step 3.a. loss was real */
                } else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
                        tp->high_seq = tp->snd_nxt;
@@ -2681,8 +2685,8 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack,
                /* A Reno DUPACK means new data in F-RTO step 2.b above are
                 * delivered. Lower inflight to clock out (re)tranmissions.
                 */
-               if (after(tp->snd_nxt, tp->high_seq) && is_dupack)
-                       tcp_add_reno_sack(sk);
+               if (after(tp->snd_nxt, tp->high_seq) && num_dupack)
+                       tcp_add_reno_sack(sk, num_dupack);
                else if (flag & FLAG_SND_UNA_ADVANCED)
                        tcp_reset_reno_sack(tp);
        }
@@ -2759,13 +2763,13 @@ static bool tcp_force_fast_retransmit(struct sock *sk)
  * tcp_xmit_retransmit_queue().
  */
 static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
-                                 bool is_dupack, int *ack_flag, int *rexmit)
+                                 int num_dupack, int *ack_flag, int *rexmit)
 {
        struct inet_connection_sock *icsk = inet_csk(sk);
        struct tcp_sock *tp = tcp_sk(sk);
        int fast_rexmit = 0, flag = *ack_flag;
-       bool do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
-                                    tcp_force_fast_retransmit(sk));
+       bool do_lost = num_dupack || ((flag & FLAG_DATA_SACKED) &&
+                                     tcp_force_fast_retransmit(sk));
 
        if (!tp->packets_out && tp->sacked_out)
                tp->sacked_out = 0;
@@ -2812,8 +2816,8 @@ static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
        switch (icsk->icsk_ca_state) {
        case TCP_CA_Recovery:
                if (!(flag & FLAG_SND_UNA_ADVANCED)) {
-                       if (tcp_is_reno(tp) && is_dupack)
-                               tcp_add_reno_sack(sk);
+                       if (tcp_is_reno(tp))
+                               tcp_add_reno_sack(sk, num_dupack);
                } else {
                        if (tcp_try_undo_partial(sk, prior_snd_una))
                                return;
@@ -2828,7 +2832,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
                tcp_identify_packet_loss(sk, ack_flag);
                break;
        case TCP_CA_Loss:
-               tcp_process_loss(sk, flag, is_dupack, rexmit);
+               tcp_process_loss(sk, flag, num_dupack, rexmit);
                tcp_identify_packet_loss(sk, ack_flag);
                if (!(icsk->icsk_ca_state == TCP_CA_Open ||
                      (*ack_flag & FLAG_LOST_RETRANS)))
@@ -2839,8 +2843,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
                if (tcp_is_reno(tp)) {
                        if (flag & FLAG_SND_UNA_ADVANCED)
                                tcp_reset_reno_sack(tp);
-                       if (is_dupack)
-                               tcp_add_reno_sack(sk);
+                       tcp_add_reno_sack(sk, num_dupack);
                }
 
                if (icsk->icsk_ca_state <= TCP_CA_Disorder)
@@ -3562,7 +3565,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
        bool is_sack_reneg = tp->is_sack_reneg;
        u32 ack_seq = TCP_SKB_CB(skb)->seq;
        u32 ack = TCP_SKB_CB(skb)->ack_seq;
-       bool is_dupack = false;
+       int num_dupack = 0;
        int prior_packets = tp->packets_out;
        u32 delivered = tp->delivered;
        u32 lost = tp->lost;
@@ -3673,8 +3676,13 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
                tcp_set_xmit_timer(sk);
 
        if (tcp_ack_is_dubious(sk, flag)) {
-               is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
-               tcp_fastretrans_alert(sk, prior_snd_una, is_dupack, &flag,
+               if (!(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP))) {
+                       num_dupack = 1;
+                       /* Consider if pure acks were aggregated in tcp_add_backlog() */
+                       if (!(flag & FLAG_DATA))
+                               num_dupack = max_t(u16, 1, skb_shinfo(skb)->gso_segs);
+               }
+               tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
                                      &rexmit);
        }
 
@@ -3692,7 +3700,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 no_queue:
        /* If data was DSACKed, see if we can undo a cwnd reduction. */
        if (flag & FLAG_DSACKING_ACK) {
-               tcp_fastretrans_alert(sk, prior_snd_una, is_dupack, &flag,
+               tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
                                      &rexmit);
                tcp_newly_delivered(sk, delivered, flag);
        }
@@ -3717,7 +3725,7 @@ old_ack:
        if (TCP_SKB_CB(skb)->sacked) {
                flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
                                                &sack_state);
-               tcp_fastretrans_alert(sk, prior_snd_una, is_dupack, &flag,
+               tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
                                      &rexmit);
                tcp_newly_delivered(sk, delivered, flag);
                tcp_xmit_recovery(sk, rexmit);