Commit 1b1fc3fd authored by Wei Wang's avatar Wei Wang Committed by David S. Miller
Browse files

tcp: make congestion control optionally skip slow start after idle 



Congestion control modules that want full control over congestion
control behavior do not want the cwnd modifications controlled by
the sysctl_tcp_slow_start_after_idle code path.
So skip those code paths for CC modules that use the cong_control()
API.
As an example, those cwnd effects are not desired for the BBR congestion
control algorithm.

Fixes: c0402760 ("tcp: new CC hook to set sending rate with rate_sample in any CA state")
Signed-off-by: default avatarWei Wang <weiwan@google.com>
Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 82486aa6

include/net/tcp.h

+3 −1
Original line number Diff line number Diff line
@@ -1234,10 +1234,12 @@ void tcp_cwnd_restart(struct sock *sk, s32 delta); 


static inline void tcp_slow_start_after_idle_check(struct sock *sk)

{

	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;

	struct tcp_sock *tp = tcp_sk(sk);

	s32 delta;



	if (!sysctl_tcp_slow_start_after_idle || tp->packets_out)

	if (!sysctl_tcp_slow_start_after_idle || tp->packets_out ||

	    ca_ops->cong_control)

		return;

	delta = tcp_time_stamp - tp->lsndtime;

	if (delta > inet_csk(sk)->icsk_rto)

net/ipv4/tcp_output.c

+3 −1
Original line number Diff line number Diff line
@@ -1514,6 +1514,7 @@ static void tcp_cwnd_application_limited(struct sock *sk) 


static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)

{

	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;

	struct tcp_sock *tp = tcp_sk(sk);



	/* Track the maximum number of outstanding packets in each
@@ -1536,7 +1537,8 @@ static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited) 
			tp->snd_cwnd_used = tp->packets_out;



		if (sysctl_tcp_slow_start_after_idle &&

		    (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)

		    (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto &&

		    !ca_ops->cong_control)

			tcp_cwnd_application_limited(sk);



		/* The following conditions together indicate the starvation

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