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Commit d4761754 authored by Yousuk Seung's avatar Yousuk Seung Committed by David S. Miller
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tcp: invalidate rate samples during SACK reneging 



Mark tcp_sock during a SACK reneging event and invalidate rate samples
while marked. Such rate samples may overestimate bw by including packets
that were SACKed before reneging.

< ack 6001 win 10000 sack 7001:38001
< ack 7001 win 0 sack 8001:38001 // Reneg detected
> seq 7001:8001 // RTO, SACK cleared.
< ack 38001 win 10000

In above example the rate sample taken after the last ack will count
7001-38001 as delivered while the actual delivery rate likely could
be much lower i.e. 7001-8001.

This patch adds a new field tcp_sock.sack_reneg and marks it when we
declare SACK reneging and entering TCP_CA_Loss, and unmarks it after
the last rate sample was taken before moving back to TCP_CA_Open. This
patch also invalidates rate samples taken while tcp_sock.is_sack_reneg
is set.

Fixes: b9f64820 ("tcp: track data delivery rate for a TCP connection")
Signed-off-by: default avatarYousuk Seung <ysseung@google.com>
Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
Acked-by: default avatarSoheil Hassas Yeganeh <soheil@google.com>
Acked-by: default avatarEric Dumazet <edumazet@google.com>
Acked-by: default avatarPriyaranjan Jha <priyarjha@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 195bd525

include/linux/tcp.h

+2 −1
Original line number Diff line number Diff line
@@ -224,7 +224,8 @@ struct tcp_sock { 
		rate_app_limited:1,  /* rate_{delivered,interval_us} limited? */

		fastopen_connect:1, /* FASTOPEN_CONNECT sockopt */

		fastopen_no_cookie:1, /* Allow send/recv SYN+data without a cookie */

		unused:3;

		is_sack_reneg:1,    /* in recovery from loss with SACK reneg? */

		unused:2;

	u8	nonagle     : 4,/* Disable Nagle algorithm?             */

		thin_lto    : 1,/* Use linear timeouts for thin streams */

		unused1	    : 1,

include/net/tcp.h

+1 −1
Original line number Diff line number Diff line
@@ -1055,7 +1055,7 @@ void tcp_rate_skb_sent(struct sock *sk, struct sk_buff *skb); 
void tcp_rate_skb_delivered(struct sock *sk, struct sk_buff *skb,

			    struct rate_sample *rs);

void tcp_rate_gen(struct sock *sk, u32 delivered, u32 lost,

		  struct rate_sample *rs);

		  bool is_sack_reneg, struct rate_sample *rs);

void tcp_rate_check_app_limited(struct sock *sk);



/* These functions determine how the current flow behaves in respect of SACK

net/ipv4/tcp.c

+1 −0
Original line number Diff line number Diff line
@@ -2412,6 +2412,7 @@ int tcp_disconnect(struct sock *sk, int flags) 
	tp->snd_cwnd_cnt = 0;

	tp->window_clamp = 0;

	tcp_set_ca_state(sk, TCP_CA_Open);

	tp->is_sack_reneg = 0;

	tcp_clear_retrans(tp);

	inet_csk_delack_init(sk);

	/* Initialize rcv_mss to TCP_MIN_MSS to avoid division by 0

net/ipv4/tcp_input.c

+8 −2
Original line number Diff line number Diff line
@@ -1942,6 +1942,8 @@ void tcp_enter_loss(struct sock *sk) 
	if (is_reneg) {

		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);

		tp->sacked_out = 0;

		/* Mark SACK reneging until we recover from this loss event. */

		tp->is_sack_reneg = 1;

	}

	tcp_clear_all_retrans_hints(tp);
@@ -2365,6 +2367,7 @@ static bool tcp_try_undo_recovery(struct sock *sk) 
		return true;

	}

	tcp_set_ca_state(sk, TCP_CA_Open);

	tp->is_sack_reneg = 0;

	return false;

}
@@ -2398,8 +2401,10 @@ static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo) 
			NET_INC_STATS(sock_net(sk),

					LINUX_MIB_TCPSPURIOUSRTOS);

		inet_csk(sk)->icsk_retransmits = 0;

		if (frto_undo || tcp_is_sack(tp))

		if (frto_undo || tcp_is_sack(tp)) {

			tcp_set_ca_state(sk, TCP_CA_Open);

			tp->is_sack_reneg = 0;

		}

		return true;

	}

	return false;
@@ -3496,6 +3501,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) 
	struct tcp_sacktag_state sack_state;

	struct rate_sample rs = { .prior_delivered = 0 };

	u32 prior_snd_una = tp->snd_una;

	bool is_sack_reneg = tp->is_sack_reneg;

	u32 ack_seq = TCP_SKB_CB(skb)->seq;

	u32 ack = TCP_SKB_CB(skb)->ack_seq;

	bool is_dupack = false;
@@ -3612,7 +3618,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) 


	delivered = tp->delivered - delivered;	/* freshly ACKed or SACKed */

	lost = tp->lost - lost;			/* freshly marked lost */

	tcp_rate_gen(sk, delivered, lost, sack_state.rate);

	tcp_rate_gen(sk, delivered, lost, is_sack_reneg, sack_state.rate);

	tcp_cong_control(sk, ack, delivered, flag, sack_state.rate);

	tcp_xmit_recovery(sk, rexmit);

	return 1;

net/ipv4/tcp_rate.c

+7 −3
Original line number Diff line number Diff line
@@ -106,7 +106,7 @@ void tcp_rate_skb_delivered(struct sock *sk, struct sk_buff *skb, 


/* Update the connection delivery information and generate a rate sample. */

void tcp_rate_gen(struct sock *sk, u32 delivered, u32 lost,

		  struct rate_sample *rs)

		  bool is_sack_reneg, struct rate_sample *rs)

{

	struct tcp_sock *tp = tcp_sk(sk);

	u32 snd_us, ack_us;
@@ -124,8 +124,12 @@ void tcp_rate_gen(struct sock *sk, u32 delivered, u32 lost, 


	rs->acked_sacked = delivered;	/* freshly ACKed or SACKed */

	rs->losses = lost;		/* freshly marked lost */

	/* Return an invalid sample if no timing information is available. */

	if (!rs->prior_mstamp) {

	/* Return an invalid sample if no timing information is available or

	 * in recovery from loss with SACK reneging. Rate samples taken during

	 * a SACK reneging event may overestimate bw by including packets that

	 * were SACKed before the reneg.

	 */

	if (!rs->prior_mstamp || is_sack_reneg) {

		rs->delivered = -1;

		rs->interval_us = -1;

		return;