tcp_bbr: add bbr_check_probe_rtt_done() helper

This patch add a helper function bbr_check_probe_rtt_done() to
  1. check the condition to see if bbr should exit probe_rtt mode;
  2. process the logic of exiting probe_rtt mode.

Fixes: 0f8782ea1497 ("tcp_bbr: add BBR congestion control")
Signed-off-by: Kevin Yang <yyd@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Reviewed-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c
index 13d3442..fd7bccf 100644 (file)
--- a/net/ipv4/tcp_bbr.c
+++ b/net/ipv4/tcp_bbr.c
@@ -95,11 +95,10 @@ struct bbr {
        u32     mode:3,              /* current bbr_mode in state machine */
                prev_ca_state:3,     /* CA state on previous ACK */
                packet_conservation:1,  /* use packet conservation? */
-               restore_cwnd:1,      /* decided to revert cwnd to old value */
                round_start:1,       /* start of packet-timed tx->ack round? */
                idle_restart:1,      /* restarting after idle? */
                probe_rtt_round_done:1,  /* a BBR_PROBE_RTT round at 4 pkts? */
-               unused:12,
+               unused:13,
                lt_is_sampling:1,    /* taking long-term ("LT") samples now? */
                lt_rtt_cnt:7,        /* round trips in long-term interval */
                lt_use_bw:1;         /* use lt_bw as our bw estimate? */
@@ -396,17 +395,11 @@ static bool bbr_set_cwnd_to_recover_or_restore(
                cwnd = tcp_packets_in_flight(tp) + acked;
        } else if (prev_state >= TCP_CA_Recovery && state < TCP_CA_Recovery) {
                /* Exiting loss recovery; restore cwnd saved before recovery. */
-               bbr->restore_cwnd = 1;
+               cwnd = max(cwnd, bbr->prior_cwnd);
                bbr->packet_conservation = 0;
        }
        bbr->prev_ca_state = state;
 
-       if (bbr->restore_cwnd) {
-               /* Restore cwnd after exiting loss recovery or PROBE_RTT. */
-               cwnd = max(cwnd, bbr->prior_cwnd);
-               bbr->restore_cwnd = 0;
-       }
-
        if (bbr->packet_conservation) {
                *new_cwnd = max(cwnd, tcp_packets_in_flight(tp) + acked);
                return true;    /* yes, using packet conservation */
@@ -748,6 +741,20 @@ static void bbr_check_drain(struct sock *sk, const struct rate_sample *rs)
                bbr_reset_probe_bw_mode(sk);  /* we estimate queue is drained */
 }
 
+static void bbr_check_probe_rtt_done(struct sock *sk)
+{
+       struct tcp_sock *tp = tcp_sk(sk);
+       struct bbr *bbr = inet_csk_ca(sk);
+
+       if (!(bbr->probe_rtt_done_stamp &&
+             after(tcp_jiffies32, bbr->probe_rtt_done_stamp)))
+               return;
+
+       bbr->min_rtt_stamp = tcp_jiffies32;  /* wait a while until PROBE_RTT */
+       tp->snd_cwnd = max(tp->snd_cwnd, bbr->prior_cwnd);
+       bbr_reset_mode(sk);
+}
+
 /* The goal of PROBE_RTT mode is to have BBR flows cooperatively and
  * periodically drain the bottleneck queue, to converge to measure the true
  * min_rtt (unloaded propagation delay). This allows the flows to keep queues
@@ -806,12 +813,8 @@ static void bbr_update_min_rtt(struct sock *sk, const struct rate_sample *rs)
                } else if (bbr->probe_rtt_done_stamp) {
                        if (bbr->round_start)
                                bbr->probe_rtt_round_done = 1;
-                       if (bbr->probe_rtt_round_done &&
-                           after(tcp_jiffies32, bbr->probe_rtt_done_stamp)) {
-                               bbr->min_rtt_stamp = tcp_jiffies32;
-                               bbr->restore_cwnd = 1;  /* snap to prior_cwnd */
-                               bbr_reset_mode(sk);
-                       }
+                       if (bbr->probe_rtt_round_done)
+                               bbr_check_probe_rtt_done(sk);
                }
        }
        /* Restart after idle ends only once we process a new S/ACK for data */
@@ -862,7 +865,6 @@ static void bbr_init(struct sock *sk)
        bbr->has_seen_rtt = 0;
        bbr_init_pacing_rate_from_rtt(sk);
 
-       bbr->restore_cwnd = 0;
        bbr->round_start = 0;
        bbr->idle_restart = 0;
        bbr->full_bw_reached = 0;