From: Neal Cardwell <ncardwell@google.com>

Date: Fri, 14 Jul 2017 17:49:23 -0400

Subject: [PATCH] tcp_bbr: introduce bbr_init_pacing_rate_from_rtt() helper

References: bnc#1060662

Patch-mainline: v4.12.6

Git-commit: 79135b89b8af304456bd67916b80116ddf03d7b6

[ 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 <ncardwell@google.com>

Signed-off-by: Yuchung Cheng <ycheng@google.com>

Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>

Signed-off-by: David S. Miller <davem@davemloft.net>

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Jiri Slaby <jslaby@suse.cz>

---

 net/ipv4/tcp_bbr.c | 23 ++++++++++++++++++-----

 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c

index 14e0eba7aa7a..e69c8b44568a 100644

--- a/net/ipv4/tcp_bbr.c

+++ b/net/ipv4/tcp_bbr.c

@@ -222,6 +222,23 @@ static u32 bbr_bw_to_pacing_rate(struct sock *sk, u32 bw, int gain)

 	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

@@ -806,7 +823,6 @@ 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 */

@@ -822,11 +838,8 @@ 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;

-- 

2.14.2