tcp: invalidate rate samples during SACK reneging

PATCH In review Yousuk Seung 2 participants 2 messages Dec 7, 2017 – Dec 8, 2017

Subsystems (3)

Networking Network drivers TCP

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Yousuk Seung

author

2017-12-07 21:41 UTC #0 lore raw

PATCH 1/1 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

Quoted 1 line

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 b9f64820fb22 ("tcp: track data delivery rate for a TCP connection")

Signed-off-by Yousuk Seung <[email protected]>

Signed-off-by Neal Cardwell <[email protected]>

Signed-off-by Yuchung Cheng <[email protected]>

Acked-by Soheil Hassas Yeganeh <[email protected]>

Acked-by Eric Dumazet <[email protected]>

Acked-by Priyaranjan Jha <[email protected]>

---
 include/linux/tcp.h  |  3 ++-
 include/net/tcp.h    |  2 +-
 net/ipv4/tcp.c       |  1 +
 net/ipv4/tcp_input.c | 10 ++++++++--
 net/ipv4/tcp_rate.c  | 10 +++++++---
 5 files changed, 19 insertions(+), 7 deletions(-)

include/linux/tcp.h +2 -1

index df5d97a85e1a..ca4a6361389b 100644
@@ -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

index 6998707e81f3..6da880d2f022 100644
@@ -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

index bf97317e6c97..f08eebe60446 100644
@@ -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

index 734cfc8ff76e..7b9e8b99b28d 100644
@@ -1941,6 +1941,8 @@ 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);

@@ -2364,6 +2366,7 @@ 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;
 }

@@ -2397,8 +2400,10 @@ 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;

@@ -3495,6 +3500,7 @@ 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;

@@ -3611,7 +3617,7 @@ 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

index 3330a370d306..c61240e43923 100644
@@ -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;

Signature · 1 line

2.15.1.424.g9478a66081-goog

David Miller

maintainer

2017-12-08 15:07 UTC #1 lore raw

From: Yousuk Seung <[email protected]>
Date: Thu, 7 Dec 2017 13:41:34 -0800

Quoted 19 lines

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
Quoted 1 line
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.

Quoted 7 lines

Fixes b9f64820fb22 ("tcp: track data delivery rate for a TCP connection")
Signed-off-by Yousuk Seung <[email protected]>
Signed-off-by Neal Cardwell <[email protected]>
Signed-off-by Yuchung Cheng <[email protected]>
Acked-by Soheil Hassas Yeganeh <[email protected]>
Acked-by Eric Dumazet <[email protected]>
Acked-by Priyaranjan Jha <[email protected]>

Applied and queued up for -stable.