Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 3c1693f0 authored by David S. Miller's avatar David S. Miller
Browse files

Merge branch 'tcp-min-rtt' 



Yuchung Cheng says:

====================
tcp: do not use RTT from delayed ACKs for min-RTT

This patch set prevents TCP sender from using RTT samples from
(suspected) delayed ACKs as the minimum RTT, to avoid unbounded
over-estimation of the network path delay. This issue is common
when a connection has extended periods of one packet chit-chat
beyond the min RTT filter window. The first patch does that for TCP
general min RTT estimation. The second patch addresses specifically
the BBR congestion control's min RTT filter.
====================

Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parents 60c25306 e4286603

include/net/tcp.h

+1 −0
Original line number Original line Diff line number Diff line
@@ -953,6 +953,7 @@ struct rate_sample { 
	u32  prior_in_flight;	/* in flight before this ACK */

	u32  prior_in_flight;	/* in flight before this ACK */

	bool is_app_limited;	/* is sample from packet with bubble in pipe? */

	bool is_app_limited;	/* is sample from packet with bubble in pipe? */

	bool is_retrans;	/* is sample from retransmission? */

	bool is_retrans;	/* is sample from retransmission? */

	bool is_ack_delayed;	/* is this (likely) a delayed ACK? */

};

};





struct tcp_congestion_ops {

struct tcp_congestion_ops {

net/ipv4/tcp_bbr.c

+2 −1
Original line number Original line Diff line number Diff line
@@ -766,7 +766,8 @@ static void bbr_update_min_rtt(struct sock *sk, const struct rate_sample *rs) 
	filter_expired = after(tcp_jiffies32,

	filter_expired = after(tcp_jiffies32,

			       bbr->min_rtt_stamp + bbr_min_rtt_win_sec * HZ);

			       bbr->min_rtt_stamp + bbr_min_rtt_win_sec * HZ);

	if (rs->rtt_us >= 0 &&

	if (rs->rtt_us >= 0 &&

	    (rs->rtt_us <= bbr->min_rtt_us || filter_expired)) {

	    (rs->rtt_us <= bbr->min_rtt_us ||

	     (filter_expired && !rs->is_ack_delayed))) {

		bbr->min_rtt_us = rs->rtt_us;

		bbr->min_rtt_us = rs->rtt_us;

		bbr->min_rtt_stamp = tcp_jiffies32;

		bbr->min_rtt_stamp = tcp_jiffies32;

	}

	}

net/ipv4/tcp_input.c

+22 −2
Original line number Original line Diff line number Diff line
@@ -97,6 +97,7 @@ int sysctl_tcp_max_orphans __read_mostly = NR_FILE; 
#define FLAG_SACK_RENEGING	0x2000 /* snd_una advanced to a sacked seq */

#define FLAG_SACK_RENEGING	0x2000 /* snd_una advanced to a sacked seq */

#define FLAG_UPDATE_TS_RECENT	0x4000 /* tcp_replace_ts_recent() */

#define FLAG_UPDATE_TS_RECENT	0x4000 /* tcp_replace_ts_recent() */

#define FLAG_NO_CHALLENGE_ACK	0x8000 /* do not call tcp_send_challenge_ack()	*/

#define FLAG_NO_CHALLENGE_ACK	0x8000 /* do not call tcp_send_challenge_ack()	*/

#define FLAG_ACK_MAYBE_DELAYED	0x10000 /* Likely a delayed ACK */





#define FLAG_ACKED		(FLAG_DATA_ACKED|FLAG_SYN_ACKED)

#define FLAG_ACKED		(FLAG_DATA_ACKED|FLAG_SYN_ACKED)

#define FLAG_NOT_DUP		(FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)

#define FLAG_NOT_DUP		(FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
@@ -2857,11 +2858,18 @@ static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una, 
	*rexmit = REXMIT_LOST;

	*rexmit = REXMIT_LOST;

}

}





static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us)

static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us, const int flag)

{

{

	u32 wlen = sock_net(sk)->ipv4.sysctl_tcp_min_rtt_wlen * HZ;

	u32 wlen = sock_net(sk)->ipv4.sysctl_tcp_min_rtt_wlen * HZ;

	struct tcp_sock *tp = tcp_sk(sk);

	struct tcp_sock *tp = tcp_sk(sk);





	if ((flag & FLAG_ACK_MAYBE_DELAYED) && rtt_us > tcp_min_rtt(tp)) {

		/* If the remote keeps returning delayed ACKs, eventually

		 * the min filter would pick it up and overestimate the

		 * prop. delay when it expires. Skip suspected delayed ACKs.

		 */

		return;

	}

	minmax_running_min(&tp->rtt_min, wlen, tcp_jiffies32,

	minmax_running_min(&tp->rtt_min, wlen, tcp_jiffies32,

			   rtt_us ? : jiffies_to_usecs(1));

			   rtt_us ? : jiffies_to_usecs(1));

}

}
@@ -2901,7 +2909,7 @@ static bool tcp_ack_update_rtt(struct sock *sk, const int flag, 
	 * always taken together with ACK, SACK, or TS-opts. Any negative

	 * always taken together with ACK, SACK, or TS-opts. Any negative

	 * values will be skipped with the seq_rtt_us < 0 check above.

	 * values will be skipped with the seq_rtt_us < 0 check above.

	 */

	 */

	tcp_update_rtt_min(sk, ca_rtt_us);

	tcp_update_rtt_min(sk, ca_rtt_us, flag);

	tcp_rtt_estimator(sk, seq_rtt_us);

	tcp_rtt_estimator(sk, seq_rtt_us);

	tcp_set_rto(sk);

	tcp_set_rto(sk);
@@ -3125,6 +3133,17 @@ static int tcp_clean_rtx_queue(struct sock *sk, u32 prior_fack, 
	if (likely(first_ackt) && !(flag & FLAG_RETRANS_DATA_ACKED)) {

	if (likely(first_ackt) && !(flag & FLAG_RETRANS_DATA_ACKED)) {

		seq_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, first_ackt);

		seq_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, first_ackt);

		ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, last_ackt);

		ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, last_ackt);



		if (pkts_acked == 1 && last_in_flight < tp->mss_cache &&

		    last_in_flight && !prior_sacked && fully_acked &&

		    sack->rate->prior_delivered + 1 == tp->delivered &&

		    !(flag & (FLAG_CA_ALERT | FLAG_SYN_ACKED))) {

			/* Conservatively mark a delayed ACK. It's typically

			 * from a lone runt packet over the round trip to

			 * a receiver w/o out-of-order or CE events.

			 */

			flag |= FLAG_ACK_MAYBE_DELAYED;

		}

	}

	}

	if (sack->first_sackt) {

	if (sack->first_sackt) {

		sack_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->first_sackt);

		sack_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->first_sackt);
@@ -3614,6 +3633,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) 




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

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

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

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

	rs.is_ack_delayed = !!(flag & FLAG_ACK_MAYBE_DELAYED);

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

	tcp_xmit_recovery(sk, rexmit);

	tcp_xmit_recovery(sk, rexmit);