4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Neal Cardwell <ncardw...@google.com>


[ Upstream commit 79135b89b8af304456bd67916b80116ddf03d7b6 ]

Introduce a helper to initialize the BBR pacing rate unconditionally,
based on the current cwnd and RTT estimate. This is a pure refactor,
but is needed for two following fixes.

Fixes: 0f8782ea1497 ("tcp_bbr: add BBR congestion control")
Signed-off-by: Neal Cardwell <ncardw...@google.com>
Signed-off-by: Yuchung Cheng <ych...@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soh...@google.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 net/ipv4/tcp_bbr.c |   23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

--- a/net/ipv4/tcp_bbr.c
+++ b/net/ipv4/tcp_bbr.c
@@ -192,6 +192,23 @@ static u32 bbr_bw_to_pacing_rate(struct
        return rate;
 }
 
+/* Initialize pacing rate to: high_gain * init_cwnd / RTT. */
+static void bbr_init_pacing_rate_from_rtt(struct sock *sk)
+{
+       struct tcp_sock *tp = tcp_sk(sk);
+       u64 bw;
+       u32 rtt_us;
+
+       if (tp->srtt_us) {              /* any RTT sample yet? */
+               rtt_us = max(tp->srtt_us >> 3, 1U);
+       } else {                         /* no RTT sample yet */
+               rtt_us = USEC_PER_MSEC;  /* use nominal default RTT */
+       }
+       bw = (u64)tp->snd_cwnd * BW_UNIT;
+       do_div(bw, rtt_us);
+       sk->sk_pacing_rate = bbr_bw_to_pacing_rate(sk, bw, bbr_high_gain);
+}
+
 /* Pace using current bw estimate and a gain factor. In order to help drive the
  * network toward lower queues while maintaining high utilization and low
  * latency, the average pacing rate aims to be slightly (~1%) lower than the
@@ -776,7 +793,6 @@ static void bbr_init(struct sock *sk)
 {
        struct tcp_sock *tp = tcp_sk(sk);
        struct bbr *bbr = inet_csk_ca(sk);
-       u64 bw;
 
        bbr->prior_cwnd = 0;
        bbr->tso_segs_goal = 0;  /* default segs per skb until first ACK */
@@ -792,11 +808,8 @@ static void bbr_init(struct sock *sk)
 
        minmax_reset(&bbr->bw, bbr->rtt_cnt, 0);  /* init max bw to 0 */
 
-       /* Initialize pacing rate to: high_gain * init_cwnd / RTT. */
-       bw = (u64)tp->snd_cwnd * BW_UNIT;
-       do_div(bw, (tp->srtt_us >> 3) ? : USEC_PER_MSEC);
        sk->sk_pacing_rate = 0;         /* force an update of sk_pacing_rate */
-       bbr_set_pacing_rate(sk, bw, bbr_high_gain);
+       bbr_init_pacing_rate_from_rtt(sk);
 
        bbr->restore_cwnd = 0;
        bbr->round_start = 0;


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