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tcp: invalidate rate samples during SACK reneging

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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: b9f64820fb ("tcp: track data delivery rate for a TCP connection")
Signed-off-by: Yousuk Seung <ysseung@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Acked-by: Priyaranjan Jha <priyarjha@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Yousuk Seung 2017-12-07 13:41:34 -08:00 committed by David S. Miller
parent 195bd525d5
commit d4761754b4
5 changed files with 19 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
include/linux/tcp.h
View File

@ -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,

2
include/net/tcp.h
View File

@ -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

1
net/ipv4/tcp.c
View File

@ -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

10
net/ipv4/tcp_input.c
View File

@ -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;

10
net/ipv4/tcp_rate.c
View File

@ -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;