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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: David S. Miller <davem@davemloft.net>
This commit is contained in:
David S. Miller
commit
337f1b07db
@ -1916,6 +1916,16 @@ extern void tcp_rack_advance(struct tcp_sock *tp, u8 sacked, u32 end_seq,
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u64 xmit_time);
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extern void tcp_rack_reo_timeout(struct sock *sk);
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/* At how many usecs into the future should the RTO fire? */
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static inline s64 tcp_rto_delta_us(const struct sock *sk)
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{
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const struct sk_buff *skb = tcp_write_queue_head(sk);
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u32 rto = inet_csk(sk)->icsk_rto;
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u64 rto_time_stamp_us = skb->skb_mstamp + jiffies_to_usecs(rto);
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return rto_time_stamp_us - tcp_sk(sk)->tcp_mstamp;
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}
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/*
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* Save and compile IPv4 options, return a pointer to it
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*/
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@ -107,6 +107,7 @@ int sysctl_tcp_invalid_ratelimit __read_mostly = HZ/2;
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#define FLAG_ORIG_SACK_ACKED 0x200 /* Never retransmitted data are (s)acked */
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#define FLAG_SND_UNA_ADVANCED 0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
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#define FLAG_DSACKING_ACK 0x800 /* SACK blocks contained D-SACK info */
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#define FLAG_SET_XMIT_TIMER 0x1000 /* Set TLP or RTO timer */
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#define FLAG_SACK_RENEGING 0x2000 /* snd_una advanced to a sacked seq */
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#define FLAG_UPDATE_TS_RECENT 0x4000 /* tcp_replace_ts_recent() */
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#define FLAG_NO_CHALLENGE_ACK 0x8000 /* do not call tcp_send_challenge_ack() */
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@ -3004,10 +3005,7 @@ void tcp_rearm_rto(struct sock *sk)
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/* Offset the time elapsed after installing regular RTO */
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if (icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
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icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
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struct sk_buff *skb = tcp_write_queue_head(sk);
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u64 rto_time_stamp = skb->skb_mstamp +
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jiffies_to_usecs(rto);
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s64 delta_us = rto_time_stamp - tp->tcp_mstamp;
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s64 delta_us = tcp_rto_delta_us(sk);
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/* delta_us may not be positive if the socket is locked
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* when the retrans timer fires and is rescheduled.
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*/
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@ -3019,6 +3017,13 @@ void tcp_rearm_rto(struct sock *sk)
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}
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}
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/* Try to schedule a loss probe; if that doesn't work, then schedule an RTO. */
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static void tcp_set_xmit_timer(struct sock *sk)
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{
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if (!tcp_schedule_loss_probe(sk))
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tcp_rearm_rto(sk);
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}
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/* If we get here, the whole TSO packet has not been acked. */
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static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
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{
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@ -3180,7 +3185,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
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ca_rtt_us, sack->rate);
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if (flag & FLAG_ACKED) {
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tcp_rearm_rto(sk);
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flag |= FLAG_SET_XMIT_TIMER; /* set TLP or RTO timer */
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if (unlikely(icsk->icsk_mtup.probe_size &&
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!after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
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tcp_mtup_probe_success(sk);
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@ -3208,7 +3213,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
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* after when the head was last (re)transmitted. Otherwise the
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* timeout may continue to extend in loss recovery.
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*/
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tcp_rearm_rto(sk);
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flag |= FLAG_SET_XMIT_TIMER; /* set TLP or RTO timer */
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}
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if (icsk->icsk_ca_ops->pkts_acked) {
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@ -3580,9 +3585,6 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
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if (after(ack, tp->snd_nxt))
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goto invalid_ack;
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if (icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)
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tcp_rearm_rto(sk);
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if (after(ack, prior_snd_una)) {
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flag |= FLAG_SND_UNA_ADVANCED;
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icsk->icsk_retransmits = 0;
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@ -3647,18 +3649,20 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
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flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una, &acked,
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&sack_state);
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if (tp->tlp_high_seq)
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tcp_process_tlp_ack(sk, ack, flag);
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/* If needed, reset TLP/RTO timer; RACK may later override this. */
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if (flag & FLAG_SET_XMIT_TIMER)
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tcp_set_xmit_timer(sk);
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if (tcp_ack_is_dubious(sk, flag)) {
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is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
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tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);
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}
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if (tp->tlp_high_seq)
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tcp_process_tlp_ack(sk, ack, flag);
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if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
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sk_dst_confirm(sk);
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if (icsk->icsk_pending == ICSK_TIME_RETRANS)
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tcp_schedule_loss_probe(sk);
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delivered = tp->delivered - delivered; /* freshly ACKed or SACKed */
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lost = tp->lost - lost; /* freshly marked lost */
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tcp_rate_gen(sk, delivered, lost, sack_state.rate);
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@ -2377,24 +2377,15 @@ bool tcp_schedule_loss_probe(struct sock *sk)
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{
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struct inet_connection_sock *icsk = inet_csk(sk);
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struct tcp_sock *tp = tcp_sk(sk);
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u32 timeout, tlp_time_stamp, rto_time_stamp;
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u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);
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u32 timeout, rto_delta_us;
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/* No consecutive loss probes. */
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if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) {
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tcp_rearm_rto(sk);
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return false;
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}
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/* Don't do any loss probe on a Fast Open connection before 3WHS
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* finishes.
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*/
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if (tp->fastopen_rsk)
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return false;
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/* TLP is only scheduled when next timer event is RTO. */
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if (icsk->icsk_pending != ICSK_TIME_RETRANS)
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return false;
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/* Schedule a loss probe in 2*RTT for SACK capable connections
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* in Open state, that are either limited by cwnd or application.
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*/
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@ -2417,14 +2408,10 @@ bool tcp_schedule_loss_probe(struct sock *sk)
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(rtt + (rtt >> 1) + TCP_DELACK_MAX));
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timeout = max_t(u32, timeout, msecs_to_jiffies(10));
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/* If RTO is shorter, just schedule TLP in its place. */
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tlp_time_stamp = tcp_jiffies32 + timeout;
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rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;
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if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {
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s32 delta = rto_time_stamp - tcp_jiffies32;
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if (delta > 0)
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timeout = delta;
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}
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/* If the RTO formula yields an earlier time, then use that time. */
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rto_delta_us = tcp_rto_delta_us(sk); /* How far in future is RTO? */
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if (rto_delta_us > 0)
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timeout = min_t(u32, timeout, usecs_to_jiffies(rto_delta_us));
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inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,
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TCP_RTO_MAX);
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