From 071d5080e33d6f24139e4213c2d9f97a2c21b602 Mon Sep 17 00:00:00 2001 From: Yuchung Cheng Date: Thu, 9 Jul 2015 13:16:29 -0700 Subject: tcp: add tcp_in_slow_start helper Add a helper to test the slow start condition in various congestion control modules and other places. This is to prepare a slight improvement in policy as to exactly when to slow start. Signed-off-by: Yuchung Cheng Signed-off-by: Neal Cardwell Signed-off-by: Eric Dumazet Signed-off-by: Nandita Dukkipati Signed-off-by: David S. Miller --- net/ipv4/tcp_cong.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'net/ipv4/tcp_cong.c') diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c index 84be008c945c..654729a8cb23 100644 --- a/net/ipv4/tcp_cong.c +++ b/net/ipv4/tcp_cong.c @@ -413,7 +413,7 @@ void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked) return; /* In "safe" area, increase. */ - if (tp->snd_cwnd <= tp->snd_ssthresh) { + if (tcp_in_slow_start(tp)) { acked = tcp_slow_start(tp, acked); if (!acked) return; -- cgit v1.2.3 From 76174004a0f19785a328f40388e87e982bbf69b9 Mon Sep 17 00:00:00 2001 From: Yuchung Cheng Date: Thu, 9 Jul 2015 13:16:30 -0700 Subject: tcp: do not slow start when cwnd equals ssthresh In the original design slow start is only used to raise cwnd when cwnd is stricly below ssthresh. It makes little sense to slow start when cwnd == ssthresh: especially when hystart has set ssthresh in the initial ramp, or after recovery when cwnd resets to ssthresh. Not doing so will also help reduce the buffer bloat slightly. Signed-off-by: Yuchung Cheng Signed-off-by: Neal Cardwell Signed-off-by: Eric Dumazet Signed-off-by: Nandita Dukkipati Signed-off-by: David S. Miller --- include/net/tcp.h | 2 +- net/ipv4/tcp_cdg.c | 2 +- net/ipv4/tcp_cong.c | 4 +--- net/ipv4/tcp_hybla.c | 2 +- 4 files changed, 4 insertions(+), 6 deletions(-) (limited to 'net/ipv4/tcp_cong.c') diff --git a/include/net/tcp.h b/include/net/tcp.h index dba22fc1b065..364426a2be5a 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -991,7 +991,7 @@ static inline unsigned int tcp_packets_in_flight(const struct tcp_sock *tp) static inline bool tcp_in_slow_start(const struct tcp_sock *tp) { - return tp->snd_cwnd <= tp->snd_ssthresh; + return tp->snd_cwnd < tp->snd_ssthresh; } static inline bool tcp_in_initial_slowstart(const struct tcp_sock *tp) diff --git a/net/ipv4/tcp_cdg.c b/net/ipv4/tcp_cdg.c index 8c6fd3d5e40f..167b6a3e1b98 100644 --- a/net/ipv4/tcp_cdg.c +++ b/net/ipv4/tcp_cdg.c @@ -264,7 +264,7 @@ static void tcp_cdg_cong_avoid(struct sock *sk, u32 ack, u32 acked) u32 prior_snd_cwnd; u32 incr; - if (tp->snd_cwnd < tp->snd_ssthresh && hystart_detect) + if (tcp_in_slow_start(tp) && hystart_detect) tcp_cdg_hystart_update(sk); if (after(ack, ca->rtt_seq) && ca->rtt.v64) { diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c index 654729a8cb23..a2ed23c595cf 100644 --- a/net/ipv4/tcp_cong.c +++ b/net/ipv4/tcp_cong.c @@ -365,10 +365,8 @@ int tcp_set_congestion_control(struct sock *sk, const char *name) */ u32 tcp_slow_start(struct tcp_sock *tp, u32 acked) { - u32 cwnd = tp->snd_cwnd + acked; + u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh); - if (cwnd > tp->snd_ssthresh) - cwnd = tp->snd_ssthresh + 1; acked -= cwnd - tp->snd_cwnd; tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp); diff --git a/net/ipv4/tcp_hybla.c b/net/ipv4/tcp_hybla.c index f963b274f2b0..083831e359df 100644 --- a/net/ipv4/tcp_hybla.c +++ b/net/ipv4/tcp_hybla.c @@ -112,7 +112,7 @@ static void hybla_cong_avoid(struct sock *sk, u32 ack, u32 acked) rho_fractions = ca->rho_3ls - (ca->rho << 3); - if (tp->snd_cwnd < tp->snd_ssthresh) { + if (tcp_in_slow_start(tp)) { /* * slow start * INC = 2^RHO - 1 -- cgit v1.2.3