tcp: consolidate congestion control undo functions

Most TCP congestion controls are using identical logic to undo
cwnd except BBR. This patch consolidates these similar functions
to the one used currently by Reno and others.

Suggested-by: Neal Cardwell <[e-mail]>
Signed-off-by: Yuchung Cheng <[e-mail]>
Signed-off-by: Neal Cardwell <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv4/tcp_bic.c

···
 struct bictcp {
 	u32	cnt;		/* increase cwnd by 1 after ACKs */
 	u32	last_max_cwnd;	/* last maximum snd_cwnd */
-	u32	loss_cwnd;	/* congestion window at last loss */
 	u32	last_cwnd;	/* the last snd_cwnd */
 	u32	last_time;	/* time when updated last_cwnd */
 	u32	epoch_start;	/* beginning of an epoch */
···
 	struct bictcp *ca = inet_csk_ca(sk);
 
 	bictcp_reset(ca);
-	ca->loss_cwnd = 0;
 
 	if (initial_ssthresh)
 		tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
···
 	else
 		ca->last_max_cwnd = tp->snd_cwnd;
 
-	ca->loss_cwnd = tp->snd_cwnd;
-
 	if (tp->snd_cwnd <= low_window)
 		return max(tp->snd_cwnd >> 1U, 2U);
 	else
 		return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
-}
-
-static u32 bictcp_undo_cwnd(struct sock *sk)
-{
-	const struct tcp_sock *tp = tcp_sk(sk);
-	const struct bictcp *ca = inet_csk_ca(sk);
-
-	return max(tp->snd_cwnd, ca->loss_cwnd);
 }
 
 static void bictcp_state(struct sock *sk, u8 new_state)
···
 	.ssthresh	= bictcp_recalc_ssthresh,
 	.cong_avoid	= bictcp_cong_avoid,
 	.set_state	= bictcp_state,
-	.undo_cwnd	= bictcp_undo_cwnd,
+	.undo_cwnd	= tcp_reno_undo_cwnd,
 	.pkts_acked     = bictcp_acked,
 	.owner		= THIS_MODULE,
 	.name		= "bic",

net/ipv4/tcp_cdg.c

···
 	u8  state;
 	u8  delack;
 	u32 rtt_seq;
-	u32 undo_cwnd;
 	u32 shadow_wnd;
 	u16 backoff_cnt;
 	u16 sample_cnt;
···
 	struct cdg *ca = inet_csk_ca(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
 
-	ca->undo_cwnd = tp->snd_cwnd;
-
 	if (ca->state == CDG_BACKOFF)
 		return max(2U, (tp->snd_cwnd * min(1024U, backoff_beta)) >> 10);
 
···
 	if (use_shadow)
 		return max3(2U, ca->shadow_wnd, tp->snd_cwnd >> 1);
 	return max(2U, tp->snd_cwnd >> 1);
-}
-
-static u32 tcp_cdg_undo_cwnd(struct sock *sk)
-{
-	struct cdg *ca = inet_csk_ca(sk);
-
-	return max(tcp_sk(sk)->snd_cwnd, ca->undo_cwnd);
 }
 
 static void tcp_cdg_cwnd_event(struct sock *sk, const enum tcp_ca_event ev)
···
 	.cong_avoid = tcp_cdg_cong_avoid,
 	.cwnd_event = tcp_cdg_cwnd_event,
 	.pkts_acked = tcp_cdg_acked,
-	.undo_cwnd = tcp_cdg_undo_cwnd,
+	.undo_cwnd = tcp_reno_undo_cwnd,
 	.ssthresh = tcp_cdg_ssthresh,
 	.release = tcp_cdg_release,
 	.init = tcp_cdg_init,

net/ipv4/tcp_cubic.c

···
 struct bictcp {
 	u32	cnt;		/* increase cwnd by 1 after ACKs */
 	u32	last_max_cwnd;	/* last maximum snd_cwnd */
-	u32	loss_cwnd;	/* congestion window at last loss */
 	u32	last_cwnd;	/* the last snd_cwnd */
 	u32	last_time;	/* time when updated last_cwnd */
 	u32	bic_origin_point;/* origin point of bic function */
···
 	struct bictcp *ca = inet_csk_ca(sk);
 
 	bictcp_reset(ca);
-	ca->loss_cwnd = 0;
 
 	if (hystart)
 		bictcp_hystart_reset(sk);
···
 	else
 		ca->last_max_cwnd = tp->snd_cwnd;
 
-	ca->loss_cwnd = tp->snd_cwnd;
-
 	return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
-}
-
-static u32 bictcp_undo_cwnd(struct sock *sk)
-{
-	struct bictcp *ca = inet_csk_ca(sk);
-
-	return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
 }
 
 static void bictcp_state(struct sock *sk, u8 new_state)
···
 	.ssthresh	= bictcp_recalc_ssthresh,
 	.cong_avoid	= bictcp_cong_avoid,
 	.set_state	= bictcp_state,
-	.undo_cwnd	= bictcp_undo_cwnd,
+	.undo_cwnd	= tcp_reno_undo_cwnd,
 	.cwnd_event	= bictcp_cwnd_event,
 	.pkts_acked     = bictcp_acked,
 	.owner		= THIS_MODULE,

net/ipv4/tcp_highspeed.c

···
 
 struct hstcp {
 	u32	ai;
-	u32	loss_cwnd;
 };
 
 static void hstcp_init(struct sock *sk)
···
 	const struct tcp_sock *tp = tcp_sk(sk);
 	struct hstcp *ca = inet_csk_ca(sk);
 
-	ca->loss_cwnd = tp->snd_cwnd;
 	/* Do multiplicative decrease */
 	return max(tp->snd_cwnd - ((tp->snd_cwnd * hstcp_aimd_vals[ca->ai].md) >> 8), 2U);
-}
-
-static u32 hstcp_cwnd_undo(struct sock *sk)
-{
-	const struct hstcp *ca = inet_csk_ca(sk);
-
-	return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
 }
 
 static struct tcp_congestion_ops tcp_highspeed __read_mostly = {
 	.init		= hstcp_init,
 	.ssthresh	= hstcp_ssthresh,
-	.undo_cwnd	= hstcp_cwnd_undo,
+	.undo_cwnd	= tcp_reno_undo_cwnd,
 	.cong_avoid	= hstcp_cong_avoid,
 
 	.owner		= THIS_MODULE,

net/ipv4/tcp_illinois.c

···
 	u32	end_seq;	/* right edge of current RTT */
 	u32	alpha;		/* Additive increase */
 	u32	beta;		/* Muliplicative decrease */
-	u32	loss_cwnd;	/* cwnd on loss */
 	u16	acked;		/* # packets acked by current ACK */
 	u8	rtt_above;	/* average rtt has gone above threshold */
 	u8	rtt_low;	/* # of rtts measurements below threshold */
···
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct illinois *ca = inet_csk_ca(sk);
 
-	ca->loss_cwnd = tp->snd_cwnd;
 	/* Multiplicative decrease */
 	return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->beta) >> BETA_SHIFT), 2U);
-}
-
-static u32 tcp_illinois_cwnd_undo(struct sock *sk)
-{
-	const struct illinois *ca = inet_csk_ca(sk);
-
-	return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
 }
 
 /* Extract info for Tcp socket info provided via netlink. */
···
 static struct tcp_congestion_ops tcp_illinois __read_mostly = {
 	.init		= tcp_illinois_init,
 	.ssthresh	= tcp_illinois_ssthresh,
-	.undo_cwnd	= tcp_illinois_cwnd_undo,
+	.undo_cwnd	= tcp_reno_undo_cwnd,
 	.cong_avoid	= tcp_illinois_cong_avoid,
 	.set_state	= tcp_illinois_state,
 	.get_info	= tcp_illinois_info,

net/ipv4/tcp_nv.c

···
 				 * < 0 => less than 1 packet/RTT */
 	u8  available8;
 	u16 available16;
-	u32 loss_cwnd;	/* cwnd at last loss */
 	u8  nv_allow_cwnd_growth:1, /* whether cwnd can grow */
 		nv_reset:1,	    /* whether to reset values */
 		nv_catchup:1;	    /* whether we are growing because
···
 	struct tcp_sock *tp = tcp_sk(sk);
 
 	ca->nv_reset = 0;
-	ca->loss_cwnd = 0;
 	ca->nv_no_cong_cnt = 0;
 	ca->nv_rtt_cnt = 0;
 	ca->nv_last_rtt = 0;
···
 static u32 tcpnv_recalc_ssthresh(struct sock *sk)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
-	struct tcpnv *ca = inet_csk_ca(sk);
 
-	ca->loss_cwnd = tp->snd_cwnd;
 	return max((tp->snd_cwnd * nv_loss_dec_factor) >> 10, 2U);
-}
-
-static u32 tcpnv_undo_cwnd(struct sock *sk)
-{
-	struct tcpnv *ca = inet_csk_ca(sk);
-
-	return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
 }
 
 static void tcpnv_state(struct sock *sk, u8 new_state)
···
 	.ssthresh	= tcpnv_recalc_ssthresh,
 	.cong_avoid	= tcpnv_cong_avoid,
 	.set_state	= tcpnv_state,
-	.undo_cwnd	= tcpnv_undo_cwnd,
+	.undo_cwnd	= tcp_reno_undo_cwnd,
 	.pkts_acked     = tcpnv_acked,
 	.get_info	= tcpnv_get_info,
 

net/ipv4/tcp_scalable.c

···
 #define TCP_SCALABLE_AI_CNT	50U
 #define TCP_SCALABLE_MD_SCALE	3
 
-struct scalable {
-	u32 loss_cwnd;
-};
-
 static void tcp_scalable_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
···
 static u32 tcp_scalable_ssthresh(struct sock *sk)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
-	struct scalable *ca = inet_csk_ca(sk);
-
-	ca->loss_cwnd = tp->snd_cwnd;
 
 	return max(tp->snd_cwnd - (tp->snd_cwnd>>TCP_SCALABLE_MD_SCALE), 2U);
 }
 
-static u32 tcp_scalable_cwnd_undo(struct sock *sk)
-{
-	const struct scalable *ca = inet_csk_ca(sk);
-
-	return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
-}
-
 static struct tcp_congestion_ops tcp_scalable __read_mostly = {
 	.ssthresh	= tcp_scalable_ssthresh,
-	.undo_cwnd	= tcp_scalable_cwnd_undo,
+	.undo_cwnd	= tcp_reno_undo_cwnd,
 	.cong_avoid	= tcp_scalable_cong_avoid,
 
 	.owner		= THIS_MODULE,

net/ipv4/tcp_veno.c

···
 	u32 basertt;		/* the min of all Veno rtt measurements seen (in usec) */
 	u32 inc;		/* decide whether to increase cwnd */
 	u32 diff;		/* calculate the diff rate */
-	u32 loss_cwnd;		/* cwnd when loss occured */
 };
 
 /* There are several situations when we must "re-start" Veno:
···
 	const struct tcp_sock *tp = tcp_sk(sk);
 	struct veno *veno = inet_csk_ca(sk);
 
-	veno->loss_cwnd = tp->snd_cwnd;
 	if (veno->diff < beta)
 		/* in "non-congestive state", cut cwnd by 1/5 */
 		return max(tp->snd_cwnd * 4 / 5, 2U);
···
 		return max(tp->snd_cwnd >> 1U, 2U);
 }
 
-static u32 tcp_veno_cwnd_undo(struct sock *sk)
-{
-	const struct veno *veno = inet_csk_ca(sk);
-
-	return max(tcp_sk(sk)->snd_cwnd, veno->loss_cwnd);
-}
-
 static struct tcp_congestion_ops tcp_veno __read_mostly = {
 	.init		= tcp_veno_init,
 	.ssthresh	= tcp_veno_ssthresh,
-	.undo_cwnd	= tcp_veno_cwnd_undo,
+	.undo_cwnd	= tcp_reno_undo_cwnd,
 	.cong_avoid	= tcp_veno_cong_avoid,
 	.pkts_acked	= tcp_veno_pkts_acked,
 	.set_state	= tcp_veno_state,

net/ipv4/tcp_yeah.c

···
 	u32 fast_count;
 
 	u32 pkts_acked;
-	u32 loss_cwnd;
 };
 
 static void tcp_yeah_init(struct sock *sk)
···
 
 	yeah->fast_count = 0;
 	yeah->reno_count = max(yeah->reno_count>>1, 2U);
-	yeah->loss_cwnd = tp->snd_cwnd;
 
 	return max_t(int, tp->snd_cwnd - reduction, 2);
-}
-
-static u32 tcp_yeah_cwnd_undo(struct sock *sk)
-{
-	const struct yeah *yeah = inet_csk_ca(sk);
-
-	return max(tcp_sk(sk)->snd_cwnd, yeah->loss_cwnd);
 }
 
 static struct tcp_congestion_ops tcp_yeah __read_mostly = {
 	.init		= tcp_yeah_init,
 	.ssthresh	= tcp_yeah_ssthresh,
-	.undo_cwnd      = tcp_yeah_cwnd_undo,
+	.undo_cwnd      = tcp_reno_undo_cwnd,
 	.cong_avoid	= tcp_yeah_cong_avoid,
 	.set_state	= tcp_vegas_state,
 	.cwnd_event	= tcp_vegas_cwnd_event,