Commit 337f1b07 authored by David S. Miller's avatar David S. Miller
Browse files

Merge branch 'tcp-xmit-timer-rearming' 



Neal Cardwell says:

====================
tcp: fix xmit timer rearming to avoid stalls

This patch series is a bug fix for a TCP loss recovery performance bug
reported independently in recent netdev threads:

 (i)  July 26, 2017: netdev thread "TCP fast retransmit issues"
 (ii) July 26, 2017: netdev thread:
       "[PATCH V2 net-next] TLP: Don't reschedule PTO when there's one
       outstanding TLP retransmission"

Many thanks to Klavs Klavsen and Mao Wenan for the detailed reports,
traces, and packetdrill test cases, which enabled us to root-cause
this issue and verify the fix.

- v1 -> v2:
 - In patch 2/3, changed an unclear comment in the pre-existing code
   in tcp_schedule_loss_probe() to be more clear (thanks to Eric Dumazet
   for suggesting we improve this).
====================

Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parents b91d5329 df92c839

include/net/tcp.h

+10 −0
Original line number Diff line number Diff line
@@ -1916,6 +1916,16 @@ extern void tcp_rack_advance(struct tcp_sock *tp, u8 sacked, u32 end_seq, 
			     u64 xmit_time);

extern void tcp_rack_reo_timeout(struct sock *sk);



/* At how many usecs into the future should the RTO fire? */

static inline s64 tcp_rto_delta_us(const struct sock *sk)

{

	const struct sk_buff *skb = tcp_write_queue_head(sk);

	u32 rto = inet_csk(sk)->icsk_rto;

	u64 rto_time_stamp_us = skb->skb_mstamp + jiffies_to_usecs(rto);



	return rto_time_stamp_us - tcp_sk(sk)->tcp_mstamp;

}



/*

 * Save and compile IPv4 options, return a pointer to it

 */

net/ipv4/tcp_input.c

+17 −13
Original line number Diff line number Diff line
@@ -107,6 +107,7 @@ int sysctl_tcp_invalid_ratelimit __read_mostly = HZ/2; 
#define FLAG_ORIG_SACK_ACKED	0x200 /* Never retransmitted data are (s)acked	*/

#define FLAG_SND_UNA_ADVANCED	0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */

#define FLAG_DSACKING_ACK	0x800 /* SACK blocks contained D-SACK info */

#define FLAG_SET_XMIT_TIMER	0x1000 /* Set TLP or RTO timer */

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

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

#define FLAG_NO_CHALLENGE_ACK	0x8000 /* do not call tcp_send_challenge_ack()	*/
@@ -3004,10 +3005,7 @@ void tcp_rearm_rto(struct sock *sk) 
		/* Offset the time elapsed after installing regular RTO */

		if (icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||

		    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {

			struct sk_buff *skb = tcp_write_queue_head(sk);

			u64 rto_time_stamp = skb->skb_mstamp +

					     jiffies_to_usecs(rto);

			s64 delta_us = rto_time_stamp - tp->tcp_mstamp;

			s64 delta_us = tcp_rto_delta_us(sk);

			/* delta_us may not be positive if the socket is locked

			 * when the retrans timer fires and is rescheduled.

			 */
@@ -3019,6 +3017,13 @@ void tcp_rearm_rto(struct sock *sk) 
	}

}



/* Try to schedule a loss probe; if that doesn't work, then schedule an RTO. */

static void tcp_set_xmit_timer(struct sock *sk)

{

	if (!tcp_schedule_loss_probe(sk))

		tcp_rearm_rto(sk);

}



/* If we get here, the whole TSO packet has not been acked. */

static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)

{
@@ -3180,7 +3185,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets, 
					ca_rtt_us, sack->rate);



	if (flag & FLAG_ACKED) {

		tcp_rearm_rto(sk);

		flag |= FLAG_SET_XMIT_TIMER;  /* set TLP or RTO timer */

		if (unlikely(icsk->icsk_mtup.probe_size &&

			     !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {

			tcp_mtup_probe_success(sk);
@@ -3208,7 +3213,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets, 
		 * after when the head was last (re)transmitted. Otherwise the

		 * timeout may continue to extend in loss recovery.

		 */

		tcp_rearm_rto(sk);

		flag |= FLAG_SET_XMIT_TIMER;  /* set TLP or RTO timer */

	}



	if (icsk->icsk_ca_ops->pkts_acked) {
@@ -3580,9 +3585,6 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) 
	if (after(ack, tp->snd_nxt))

		goto invalid_ack;



	if (icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)

		tcp_rearm_rto(sk);



	if (after(ack, prior_snd_una)) {

		flag |= FLAG_SND_UNA_ADVANCED;

		icsk->icsk_retransmits = 0;
@@ -3647,18 +3649,20 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) 
	flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una, &acked,

				    &sack_state);



	if (tp->tlp_high_seq)

		tcp_process_tlp_ack(sk, ack, flag);

	/* If needed, reset TLP/RTO timer; RACK may later override this. */

	if (flag & FLAG_SET_XMIT_TIMER)

		tcp_set_xmit_timer(sk);



	if (tcp_ack_is_dubious(sk, flag)) {

		is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));

		tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);

	}

	if (tp->tlp_high_seq)

		tcp_process_tlp_ack(sk, ack, flag);



	if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))

		sk_dst_confirm(sk);



	if (icsk->icsk_pending == ICSK_TIME_RETRANS)

		tcp_schedule_loss_probe(sk);

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

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

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

net/ipv4/tcp_output.c

+5 −18
Original line number Diff line number Diff line
@@ -2377,24 +2377,15 @@ bool tcp_schedule_loss_probe(struct sock *sk) 
{

	struct inet_connection_sock *icsk = inet_csk(sk);

	struct tcp_sock *tp = tcp_sk(sk);

	u32 timeout, tlp_time_stamp, rto_time_stamp;

	u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);

	u32 timeout, rto_delta_us;



	/* No consecutive loss probes. */

	if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) {

		tcp_rearm_rto(sk);

		return false;

	}

	/* Don't do any loss probe on a Fast Open connection before 3WHS

	 * finishes.

	 */

	if (tp->fastopen_rsk)

		return false;



	/* TLP is only scheduled when next timer event is RTO. */

	if (icsk->icsk_pending != ICSK_TIME_RETRANS)

		return false;



	/* Schedule a loss probe in 2*RTT for SACK capable connections

	 * in Open state, that are either limited by cwnd or application.

	 */
@@ -2417,14 +2408,10 @@ bool tcp_schedule_loss_probe(struct sock *sk) 
				(rtt + (rtt >> 1) + TCP_DELACK_MAX));

	timeout = max_t(u32, timeout, msecs_to_jiffies(10));



	/* If RTO is shorter, just schedule TLP in its place. */

	tlp_time_stamp = tcp_jiffies32 + timeout;

	rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;

	if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {

		s32 delta = rto_time_stamp - tcp_jiffies32;

		if (delta > 0)

			timeout = delta;

	}

	/* If the RTO formula yields an earlier time, then use that time. */

	rto_delta_us = tcp_rto_delta_us(sk);  /* How far in future is RTO? */

	if (rto_delta_us > 0)

		timeout = min_t(u32, timeout, usecs_to_jiffies(rto_delta_us));



	inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,

				  TCP_RTO_MAX);

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