netdev - [PATCH net-next 1/5] tcp_cubic: optimize hystart

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Message-Id: <20191223202005.104713-2-edumazet@google.com>
Date:   Mon, 23 Dec 2019 12:20:01 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>,
        Martin KaFai Lau <kafai@...com>
Subject: [PATCH net-next 1/5] tcp_cubic: optimize hystart_update()

We do not care which bit in ca->found is set.

We avoid accessing hystart and hystart_detect unless really needed,
possibly avoiding one cache line miss.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/ipv4/tcp_cubic.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index 1b3d032a4df2a23faf8f12a9b426638fb1997fef..297936033c335ee57ba6205de50c5ef06b90da60 100644
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -381,9 +381,6 @@ static void hystart_update(struct sock *sk, u32 delay)
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct bictcp *ca = inet_csk_ca(sk);
 
-	if (ca->found & hystart_detect)
-		return;
-
 	if (hystart_detect & HYSTART_ACK_TRAIN) {
 		u32 now = bictcp_clock();
 
@@ -391,7 +388,7 @@ static void hystart_update(struct sock *sk, u32 delay)
 		if ((s32)(now - ca->last_ack) <= hystart_ack_delta) {
 			ca->last_ack = now;
 			if ((s32)(now - ca->round_start) > ca->delay_min >> 4) {
-				ca->found |= HYSTART_ACK_TRAIN;
+				ca->found = 1;
 				NET_INC_STATS(sock_net(sk),
 					      LINUX_MIB_TCPHYSTARTTRAINDETECT);
 				NET_ADD_STATS(sock_net(sk),
@@ -412,7 +409,7 @@ static void hystart_update(struct sock *sk, u32 delay)
 		} else {
 			if (ca->curr_rtt > ca->delay_min +
 			    HYSTART_DELAY_THRESH(ca->delay_min >> 3)) {
-				ca->found |= HYSTART_DELAY;
+				ca->found = 1;
 				NET_INC_STATS(sock_net(sk),
 					      LINUX_MIB_TCPHYSTARTDELAYDETECT);
 				NET_ADD_STATS(sock_net(sk),
@@ -450,7 +447,7 @@ static void bictcp_acked(struct sock *sk, const struct ack_sample *sample)
 		ca->delay_min = delay;
 
 	/* hystart triggers when cwnd is larger than some threshold */
-	if (hystart && tcp_in_slow_start(tp) &&
+	if (!ca->found && hystart && tcp_in_slow_start(tp) &&
 	    tp->snd_cwnd >= hystart_low_window)
 		hystart_update(sk, delay);
 }
-- 
2.24.1.735.g03f4e72817-goog