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 <ych...@google.com>
Signed-off-by: Neal Cardwell <ncardw...@google.com>
Signed-off-by: Eric Dumazet <eduma...@google.com>
Signed-off-by: Nandita Dukkipati <nandi...@google.com>
---
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(-)
diff --git a/include/net/tcp.h b/include/net/tcp.h
index dba22fc..364426a 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 8c6fd3d..167b6a3 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 654729a..a2ed23c 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 f963b27..083831e 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
--
2.4.3.573.g4eafbef
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