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Commit e9799183 authored by Florian Westphal's avatar Florian Westphal Committed by David S. Miller
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tcp: make undo_cwnd mandatory for congestion modules 



The undo_cwnd fallback in the stack doubles cwnd based on ssthresh,
which un-does reno halving behaviour.

It seems more appropriate to let congctl algorithms pair .ssthresh
and .undo_cwnd properly. Add a 'tcp_reno_undo_cwnd' function and wire it
up for all congestion algorithms that used to rely on the fallback.

Cc: Eric Dumazet <edumazet@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarFlorian Westphal <fw@strlen.de>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 85f7e750

include/net/tcp.h

+1 −0
Original line number Diff line number Diff line
@@ -958,6 +958,7 @@ u32 tcp_slow_start(struct tcp_sock *tp, u32 acked); 
void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked);



u32 tcp_reno_ssthresh(struct sock *sk);

u32 tcp_reno_undo_cwnd(struct sock *sk);

void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked);

extern struct tcp_congestion_ops tcp_reno;

net/ipv4/tcp_cong.c

+12 −2
Original line number Diff line number Diff line
@@ -68,8 +68,9 @@ int tcp_register_congestion_control(struct tcp_congestion_ops *ca) 
{

	int ret = 0;



	/* all algorithms must implement ssthresh and cong_avoid ops */

	if (!ca->ssthresh || !(ca->cong_avoid || ca->cong_control)) {

	/* all algorithms must implement these */

	if (!ca->ssthresh || !ca->undo_cwnd ||

	    !(ca->cong_avoid || ca->cong_control)) {

		pr_err("%s does not implement required ops\n", ca->name);

		return -EINVAL;

	}
@@ -441,10 +442,19 @@ u32 tcp_reno_ssthresh(struct sock *sk) 
}

EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);



u32 tcp_reno_undo_cwnd(struct sock *sk)

{

	const struct tcp_sock *tp = tcp_sk(sk);



	return max(tp->snd_cwnd, tp->snd_ssthresh << 1);

}

EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd);



struct tcp_congestion_ops tcp_reno = {

	.flags		= TCP_CONG_NON_RESTRICTED,

	.name		= "reno",

	.owner		= THIS_MODULE,

	.ssthresh	= tcp_reno_ssthresh,

	.cong_avoid	= tcp_reno_cong_avoid,

	.undo_cwnd	= tcp_reno_undo_cwnd,

};

net/ipv4/tcp_dctcp.c

+1 −0
Original line number Diff line number Diff line
@@ -342,6 +342,7 @@ static struct tcp_congestion_ops dctcp __read_mostly = { 
static struct tcp_congestion_ops dctcp_reno __read_mostly = {

	.ssthresh	= tcp_reno_ssthresh,

	.cong_avoid	= tcp_reno_cong_avoid,

	.undo_cwnd	= tcp_reno_undo_cwnd,

	.get_info	= dctcp_get_info,

	.owner		= THIS_MODULE,

	.name		= "dctcp-reno",

net/ipv4/tcp_hybla.c

+1 −0
Original line number Diff line number Diff line
@@ -166,6 +166,7 @@ static void hybla_cong_avoid(struct sock *sk, u32 ack, u32 acked) 
static struct tcp_congestion_ops tcp_hybla __read_mostly = {

	.init		= hybla_init,

	.ssthresh	= tcp_reno_ssthresh,

	.undo_cwnd	= tcp_reno_undo_cwnd,

	.cong_avoid	= hybla_cong_avoid,

	.set_state	= hybla_state,

net/ipv4/tcp_input.c

+1 −4
Original line number Diff line number Diff line
@@ -2394,10 +2394,7 @@ static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss) 
	if (tp->prior_ssthresh) {

		const struct inet_connection_sock *icsk = inet_csk(sk);



		if (icsk->icsk_ca_ops->undo_cwnd)

		tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);

		else

			tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);



		if (tp->prior_ssthresh > tp->snd_ssthresh) {

			tp->snd_ssthresh = tp->prior_ssthresh;