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Commit ffd177de authored by Yuchung Cheng's avatar Yuchung Cheng Committed by David S. Miller
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tcp: refactor DCTCP ECN ACK handling 

DCTCP has two parts - a new ECN signalling mechanism and the response
function to it. The first part can be used by other congestion
control for DCTCP-ECN deployed networks. This patch moves that part
into a separate tcp_dctcp.h to be used by other congestion control
module (like how Yeah uses Vegas algorithmas). For example, BBR is
experimenting such ECN signal currently
https://tinyurl.com/ietf-102-iccrg-bbr2



Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
Signed-off-by: default avatarYousuk Seung <ysseung@google.com>
Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent ed792e28

net/ipv4/tcp_dctcp.c

+4 −51
Original line number Diff line number Diff line
@@ -44,6 +44,7 @@ 
#include <linux/mm.h>

#include <net/tcp.h>

#include <linux/inet_diag.h>

#include "tcp_dctcp.h"



#define DCTCP_MAX_ALPHA	1024U
@@ -118,54 +119,6 @@ static u32 dctcp_ssthresh(struct sock *sk) 
	return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->dctcp_alpha) >> 11U), 2U);

}



/* Minimal DCTP CE state machine:

 *

 * S:	0 <- last pkt was non-CE

 *	1 <- last pkt was CE

 */



static void dctcp_ce_state_0_to_1(struct sock *sk)

{

	struct dctcp *ca = inet_csk_ca(sk);

	struct tcp_sock *tp = tcp_sk(sk);



	if (!ca->ce_state) {

		/* State has changed from CE=0 to CE=1, force an immediate

		 * ACK to reflect the new CE state. If an ACK was delayed,

		 * send that first to reflect the prior CE state.

		 */

		if (inet_csk(sk)->icsk_ack.pending & ICSK_ACK_TIMER)

			__tcp_send_ack(sk, ca->prior_rcv_nxt);

		inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;

	}



	ca->prior_rcv_nxt = tp->rcv_nxt;

	ca->ce_state = 1;



	tp->ecn_flags |= TCP_ECN_DEMAND_CWR;

}



static void dctcp_ce_state_1_to_0(struct sock *sk)

{

	struct dctcp *ca = inet_csk_ca(sk);

	struct tcp_sock *tp = tcp_sk(sk);



	if (ca->ce_state) {

		/* State has changed from CE=1 to CE=0, force an immediate

		 * ACK to reflect the new CE state. If an ACK was delayed,

		 * send that first to reflect the prior CE state.

		 */

		if (inet_csk(sk)->icsk_ack.pending & ICSK_ACK_TIMER)

			__tcp_send_ack(sk, ca->prior_rcv_nxt);

		inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;

	}



	ca->prior_rcv_nxt = tp->rcv_nxt;

	ca->ce_state = 0;



	tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;

}



static void dctcp_update_alpha(struct sock *sk, u32 flags)

{

	const struct tcp_sock *tp = tcp_sk(sk);
@@ -230,12 +183,12 @@ static void dctcp_state(struct sock *sk, u8 new_state) 


static void dctcp_cwnd_event(struct sock *sk, enum tcp_ca_event ev)

{

	struct dctcp *ca = inet_csk_ca(sk);



	switch (ev) {

	case CA_EVENT_ECN_IS_CE:

		dctcp_ce_state_0_to_1(sk);

		break;

	case CA_EVENT_ECN_NO_CE:

		dctcp_ce_state_1_to_0(sk);

		dctcp_ece_ack_update(sk, ev, &ca->prior_rcv_nxt, &ca->ce_state);

		break;

	default:

		/* Don't care for the rest. */

net/ipv4/tcp_dctcp.h

0 → 100644
+40 −0
Original line number Diff line number Diff line 
#ifndef _TCP_DCTCP_H

#define _TCP_DCTCP_H



static inline void dctcp_ece_ack_cwr(struct sock *sk, u32 ce_state)

{

	struct tcp_sock *tp = tcp_sk(sk);



	if (ce_state == 1)

		tp->ecn_flags |= TCP_ECN_DEMAND_CWR;

	else

		tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;

}



/* Minimal DCTP CE state machine:

 *

 * S:	0 <- last pkt was non-CE

 *	1 <- last pkt was CE

 */

static inline void dctcp_ece_ack_update(struct sock *sk, enum tcp_ca_event evt,

					u32 *prior_rcv_nxt, u32 *ce_state)

{

	u32 new_ce_state = (evt == CA_EVENT_ECN_IS_CE) ? 1 : 0;



	if (*ce_state != new_ce_state) {

		/* CE state has changed, force an immediate ACK to

		 * reflect the new CE state. If an ACK was delayed,

		 * send that first to reflect the prior CE state.

		 */

		if (inet_csk(sk)->icsk_ack.pending & ICSK_ACK_TIMER) {

			dctcp_ece_ack_cwr(sk, *ce_state);

			__tcp_send_ack(sk, *prior_rcv_nxt);

		}

		inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;

	}

	*prior_rcv_nxt = tcp_sk(sk)->rcv_nxt;

	*ce_state = new_ce_state;

	dctcp_ece_ack_cwr(sk, new_ce_state);

}



#endif