The retransmission and F-RTO transmission currently happen inside
recovery state processing (tcp_fastretrans_alert) but before
congestion control. This refactoring moves the logic after both
s.t. we can determine how much to send (cwnd) before deciding what to
send.
Signed-off-by: Yuchung Cheng <ych...@google.com>
Signed-off-by: Neal Cardwell <ncardw...@google.com>
Signed-off-by: Eric Dumazet <ncardw...@google.com>
---
net/ipv4/tcp_input.c | 58 +++++++++++++++++++++++++++++++++++++++++-----------
1 file changed, 46 insertions(+), 12 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 0003d40..482c0b4 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -126,6 +126,10 @@ int sysctl_tcp_invalid_ratelimit __read_mostly = HZ/2;
#define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
#define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
+#define REXMIT_NONE 0 /* no loss recovery to do */
+#define REXMIT_LOST 1 /* retransmit packets marked lost */
+#define REXMIT_NEW 2 /* FRTO-style transmit of unsent/new packets */
+
/* Adapt the MSS value used to make delayed ack decision to the
* real world.
*/
@@ -2664,7 +2668,8 @@ static 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, bool is_dupack,
+ int *rexmit)
{
struct tcp_sock *tp = tcp_sk(sk);
bool recovered = !before(tp->snd_una, tp->high_seq);
@@ -2686,10 +2691,15 @@ static void tcp_process_loss(struct sock *sk, int flag,
bool is_dupack)
tp->frto = 0; /* Step 3.a. loss was real */
} else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
tp->high_seq = tp->snd_nxt;
- __tcp_push_pending_frames(sk, tcp_current_mss(sk),
- TCP_NAGLE_OFF);
- if (after(tp->snd_nxt, tp->high_seq))
- return; /* Step 2.b */
+ /* Step 2.b. Try send new data (but deferred until cwnd
+ * is updated in tcp_ack()). Otherwise fall back to
+ * the conventional recovery.
+ */
+ if (tcp_send_head(sk) &&
+ after(tcp_wnd_end(tp), tp->snd_nxt)) {
+ *rexmit = REXMIT_NEW;
+ return;
+ }
tp->frto = 0;
}
}
@@ -2708,7 +2718,7 @@ static void tcp_process_loss(struct sock *sk, int flag,
bool is_dupack)
else if (flag & FLAG_SND_UNA_ADVANCED)
tcp_reset_reno_sack(tp);
}
- tcp_xmit_retransmit_queue(sk);
+ *rexmit = REXMIT_LOST;
}
/* Undo during fast recovery after partial ACK. */
@@ -2758,7 +2768,7 @@ static bool tcp_try_undo_partial(struct sock *sk, const
int acked,
*/
static void tcp_fastretrans_alert(struct sock *sk, const int acked,
const int prior_unsacked,
- bool is_dupack, int flag)
+ bool is_dupack, int flag, int *rexmit)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
@@ -2833,7 +2843,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const
int acked,
}
break;
case TCP_CA_Loss:
- tcp_process_loss(sk, flag, is_dupack);
+ tcp_process_loss(sk, flag, is_dupack, rexmit);
if (icsk->icsk_ca_state != TCP_CA_Open &&
!(flag & FLAG_LOST_RETRANS))
return;
@@ -2873,7 +2883,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const
int acked,
if (do_lost)
tcp_update_scoreboard(sk, fast_rexmit);
tcp_cwnd_reduction(sk, prior_unsacked, fast_rexmit, flag);
- tcp_xmit_retransmit_queue(sk);
+ *rexmit = REXMIT_LOST;
}
/* Kathleen Nichols' algorithm for tracking the minimum value of
@@ -3508,6 +3518,27 @@ static inline void tcp_in_ack_event(struct sock *sk, u32
flags)
icsk->icsk_ca_ops->in_ack_event(sk, flags);
}
+/* Congestion control has updated the cwnd already. So if we're in
+ * loss recovery then now we do any new sends (for FRTO) or
+ * retransmits (for CA_Loss or CA_recovery) that make sense.
+ */
+static void tcp_xmit_recovery(struct sock *sk, int rexmit)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (rexmit == REXMIT_NONE)
+ return;
+
+ if (unlikely(rexmit == 2)) {
+ __tcp_push_pending_frames(sk, tcp_current_mss(sk),
+ TCP_NAGLE_OFF);
+ if (after(tp->snd_nxt, tp->high_seq))
+ return;
+ tp->frto = 0;
+ }
+ tcp_xmit_retransmit_queue(sk);
+}
+
/* This routine deals with incoming acks, but not outgoing ones. */
static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
{
@@ -3522,6 +3553,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff
*skb, int flag)
int prior_packets = tp->packets_out;
const int prior_unsacked = tp->packets_out - tp->sacked_out;
int acked = 0; /* Number of packets newly acked */
+ int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */
sack_state.first_sackt.v64 = 0;
@@ -3618,7 +3650,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff
*skb, int flag)
if (tcp_ack_is_dubious(sk, flag)) {
is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
tcp_fastretrans_alert(sk, acked, prior_unsacked,
- is_dupack, flag);
+ is_dupack, flag, &rexmit);
}
if (tp->tlp_high_seq)
tcp_process_tlp_ack(sk, ack, flag);
@@ -3636,13 +3668,14 @@ static int tcp_ack(struct sock *sk, const struct
sk_buff *skb, int flag)
if (icsk->icsk_pending == ICSK_TIME_RETRANS)
tcp_schedule_loss_probe(sk);
tcp_update_pacing_rate(sk);
+ tcp_xmit_recovery(sk, rexmit);
return 1;
no_queue:
/* If data was DSACKed, see if we can undo a cwnd reduction. */
if (flag & FLAG_DSACKING_ACK)
tcp_fastretrans_alert(sk, acked, prior_unsacked,
- is_dupack, flag);
+ is_dupack, flag, &rexmit);
/* If this ack opens up a zero window, clear backoff. It was
* being used to time the probes, and is probably far higher than
* it needs to be for normal retransmission.
@@ -3666,7 +3699,8 @@ old_ack:
flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
&sack_state);
tcp_fastretrans_alert(sk, acked, prior_unsacked,
- is_dupack, flag);
+ is_dupack, flag, &rexmit);
+ tcp_xmit_recovery(sk, rexmit);
}
SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
--
2.7.0.rc3.207.g0ac5344
