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Commit 7354c8c3 authored by Florian Westphal's avatar Florian Westphal Committed by David S. Miller
Browse files

net: tcp: split ack slow/fast events from cwnd_event 



The congestion control ops "cwnd_event" currently supports
CA_EVENT_FAST_ACK and CA_EVENT_SLOW_ACK events (among others).
Both FAST and SLOW_ACK are only used by Westwood congestion
control algorithm.

This removes both flags from cwnd_event and adds a new
in_ack_event callback for this. The goal is to be able to
provide more detailed information about ACKs, such as whether
ECE flag was set, or whether the ACK resulted in a window
update.

It is required for DataCenter TCP (DCTCP) congestion control
algorithm as it makes a different choice depending on ECE being
set or not.

Joint work with Daniel Borkmann and Glenn Judd.

Signed-off-by: default avatarFlorian Westphal <fw@strlen.de>
Signed-off-by: default avatarDaniel Borkmann <dborkman@redhat.com>
Signed-off-by: default avatarGlenn Judd <glenn.judd@morganstanley.com>
Acked-by: default avatarStephen Hemminger <stephen@networkplumber.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 30e502a3

include/net/tcp.h

+6 −2
Original line number Diff line number Diff line
@@ -763,8 +763,10 @@ enum tcp_ca_event { 
	CA_EVENT_CWND_RESTART,	/* congestion window restart */

	CA_EVENT_COMPLETE_CWR,	/* end of congestion recovery */

	CA_EVENT_LOSS,		/* loss timeout */

	CA_EVENT_FAST_ACK,	/* in sequence ack */

	CA_EVENT_SLOW_ACK,	/* other ack */

};



enum tcp_ca_ack_event_flags {

	CA_ACK_SLOWPATH = (1 << 0),

};



/*
@@ -796,6 +798,8 @@ struct tcp_congestion_ops { 
	void (*set_state)(struct sock *sk, u8 new_state);

	/* call when cwnd event occurs (optional) */

	void (*cwnd_event)(struct sock *sk, enum tcp_ca_event ev);

	/* call when ack arrives (optional) */

	void (*in_ack_event)(struct sock *sk, u32 flags);

	/* new value of cwnd after loss (optional) */

	u32  (*undo_cwnd)(struct sock *sk);

	/* hook for packet ack accounting (optional) */

net/ipv4/tcp_input.c

+10 −2
Original line number Diff line number Diff line
@@ -3362,6 +3362,14 @@ static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag) 
	}

}



static inline void tcp_in_ack_event(struct sock *sk, u32 flags)

{

	const struct inet_connection_sock *icsk = inet_csk(sk);



	if (icsk->icsk_ca_ops->in_ack_event)

		icsk->icsk_ca_ops->in_ack_event(sk, flags);

}



/* This routine deals with incoming acks, but not outgoing ones. */

static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)

{
@@ -3421,7 +3429,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) 
		tp->snd_una = ack;

		flag |= FLAG_WIN_UPDATE;



		tcp_ca_event(sk, CA_EVENT_FAST_ACK);

		tcp_in_ack_event(sk, 0);



		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS);

	} else {
@@ -3439,7 +3447,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) 
		if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb)))

			flag |= FLAG_ECE;



		tcp_ca_event(sk, CA_EVENT_SLOW_ACK);

		tcp_in_ack_event(sk, CA_ACK_SLOWPATH);

	}



	/* We passed data and got it acked, remove any soft error

net/ipv4/tcp_westwood.c

+16 −12
Original line number Diff line number Diff line
@@ -220,32 +220,35 @@ static u32 tcp_westwood_bw_rttmin(const struct sock *sk) 
	return max_t(u32, (w->bw_est * w->rtt_min) / tp->mss_cache, 2);

}



static void tcp_westwood_ack(struct sock *sk, u32 ack_flags)

{

	if (ack_flags & CA_ACK_SLOWPATH) {

		struct westwood *w = inet_csk_ca(sk);



		westwood_update_window(sk);

		w->bk += westwood_acked_count(sk);



		update_rtt_min(w);

		return;

	}



	westwood_fast_bw(sk);

}



static void tcp_westwood_event(struct sock *sk, enum tcp_ca_event event)

{

	struct tcp_sock *tp = tcp_sk(sk);

	struct westwood *w = inet_csk_ca(sk);



	switch (event) {

	case CA_EVENT_FAST_ACK:

		westwood_fast_bw(sk);

		break;



	case CA_EVENT_COMPLETE_CWR:

		tp->snd_cwnd = tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);

		break;



	case CA_EVENT_LOSS:

		tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);

		/* Update RTT_min when next ack arrives */

		w->reset_rtt_min = 1;

		break;



	case CA_EVENT_SLOW_ACK:

		westwood_update_window(sk);

		w->bk += westwood_acked_count(sk);

		update_rtt_min(w);

		break;



	default:

		/* don't care */

		break;
@@ -274,6 +277,7 @@ static struct tcp_congestion_ops tcp_westwood __read_mostly = { 
	.ssthresh	= tcp_reno_ssthresh,

	.cong_avoid	= tcp_reno_cong_avoid,

	.cwnd_event	= tcp_westwood_event,

	.in_ack_event	= tcp_westwood_ack,

	.get_info	= tcp_westwood_info,

	.pkts_acked	= tcp_westwood_pkts_acked,