Enable Early Retransmit (ER), per RFC 5827. ER lowers the threshold
for triggering fast retransmit when the amount of outstanding data is
small and when no previously unsent data can be transmitted (such
- that limited transmit could be used).
+ that limited transmit could be used). Also controls the use of
+ Tail loss probe (TLP) that converts RTOs occuring due to tail
+ losses into fast recovery (draft-dukkipati-tcpm-tcp-loss-probe-01).
Possible values:
0 disables ER
1 enables ER
by a fourth of RTT. This mitigates connection falsely
recovers when network has a small degree of reordering
(less than 3 packets).
- Default: 2
+ 3 enables delayed ER and TLP.
+ 4 enables TLP only.
+ Default: 3
tcp_ecn - INTEGER
Control use of Explicit Congestion Notification (ECN) by TCP.
unused : 1;
u8 repair_queue;
u8 do_early_retrans:1,/* Enable RFC5827 early-retransmit */
- early_retrans_delayed:1, /* Delayed ER timer installed */
syn_data:1, /* SYN includes data */
syn_fastopen:1, /* SYN includes Fast Open option */
syn_data_acked:1;/* data in SYN is acked by SYN-ACK */
#define ICSK_TIME_RETRANS 1 /* Retransmit timer */
#define ICSK_TIME_DACK 2 /* Delayed ack timer */
#define ICSK_TIME_PROBE0 3 /* Zero window probe timer */
+#define ICSK_TIME_EARLY_RETRANS 4 /* Early retransmit timer */
+#define ICSK_TIME_LOSS_PROBE 5 /* Tail loss probe timer */
static inline struct inet_connection_sock *inet_csk(const struct sock *sk)
{
when = max_when;
}
- if (what == ICSK_TIME_RETRANS || what == ICSK_TIME_PROBE0) {
+ if (what == ICSK_TIME_RETRANS || what == ICSK_TIME_PROBE0 ||
+ what == ICSK_TIME_EARLY_RETRANS || what == ICSK_TIME_LOSS_PROBE) {
icsk->icsk_pending = what;
icsk->icsk_timeout = jiffies + when;
sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
extern void tcp_push_one(struct sock *, unsigned int mss_now);
extern void tcp_send_ack(struct sock *sk);
extern void tcp_send_delayed_ack(struct sock *sk);
+extern void tcp_send_loss_probe(struct sock *sk);
+extern bool tcp_schedule_loss_probe(struct sock *sk);
/* tcp_input.c */
extern void tcp_cwnd_application_limited(struct sock *sk);
static inline void tcp_enable_early_retrans(struct tcp_sock *tp)
{
tp->do_early_retrans = sysctl_tcp_early_retrans &&
- !sysctl_tcp_thin_dupack && sysctl_tcp_reordering == 3;
- tp->early_retrans_delayed = 0;
+ sysctl_tcp_early_retrans < 4 && !sysctl_tcp_thin_dupack &&
+ sysctl_tcp_reordering == 3;
}
static inline void tcp_disable_early_retrans(struct tcp_sock *tp)
LINUX_MIB_TCPFORWARDRETRANS, /* TCPForwardRetrans */
LINUX_MIB_TCPSLOWSTARTRETRANS, /* TCPSlowStartRetrans */
LINUX_MIB_TCPTIMEOUTS, /* TCPTimeouts */
+ LINUX_MIB_TCPLOSSPROBES, /* TCPLossProbes */
LINUX_MIB_TCPRENORECOVERYFAIL, /* TCPRenoRecoveryFail */
LINUX_MIB_TCPSACKRECOVERYFAIL, /* TCPSackRecoveryFail */
LINUX_MIB_TCPSCHEDULERFAILED, /* TCPSchedulerFailed */
#define EXPIRES_IN_MS(tmo) DIV_ROUND_UP((tmo - jiffies) * 1000, HZ)
- if (icsk->icsk_pending == ICSK_TIME_RETRANS) {
+ if (icsk->icsk_pending == ICSK_TIME_RETRANS ||
+ icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
+ icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
r->idiag_timer = 1;
r->idiag_retrans = icsk->icsk_retransmits;
r->idiag_expires = EXPIRES_IN_MS(icsk->icsk_timeout);
SNMP_MIB_ITEM("TCPForwardRetrans", LINUX_MIB_TCPFORWARDRETRANS),
SNMP_MIB_ITEM("TCPSlowStartRetrans", LINUX_MIB_TCPSLOWSTARTRETRANS),
SNMP_MIB_ITEM("TCPTimeouts", LINUX_MIB_TCPTIMEOUTS),
+ SNMP_MIB_ITEM("TCPLossProbes", LINUX_MIB_TCPLOSSPROBES),
SNMP_MIB_ITEM("TCPRenoRecoveryFail", LINUX_MIB_TCPRENORECOVERYFAIL),
SNMP_MIB_ITEM("TCPSackRecoveryFail", LINUX_MIB_TCPSACKRECOVERYFAIL),
SNMP_MIB_ITEM("TCPSchedulerFailed", LINUX_MIB_TCPSCHEDULERFAILED),
static int zero;
static int one = 1;
-static int two = 2;
+static int four = 4;
static int tcp_retr1_max = 255;
static int ip_local_port_range_min[] = { 1, 1 };
static int ip_local_port_range_max[] = { 65535, 65535 };
.mode = 0644,
.proc_handler = proc_dointvec_minmax,
.extra1 = &zero,
- .extra2 = &two,
+ .extra2 = &four,
},
{
.procname = "udp_mem",
int sysctl_tcp_thin_dupack __read_mostly;
int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
-int sysctl_tcp_early_retrans __read_mostly = 2;
+int sysctl_tcp_early_retrans __read_mostly = 3;
#define FLAG_DATA 0x01 /* Incoming frame contained data. */
#define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window update. */
* max(RTT/4, 2msec) unless ack has ECE mark, no RTT samples
* available, or RTO is scheduled to fire first.
*/
- if (sysctl_tcp_early_retrans < 2 || (flag & FLAG_ECE) || !tp->srtt)
+ if (sysctl_tcp_early_retrans < 2 || sysctl_tcp_early_retrans > 3 ||
+ (flag & FLAG_ECE) || !tp->srtt)
return false;
delay = max_t(unsigned long, (tp->srtt >> 5), msecs_to_jiffies(2));
if (!time_after(inet_csk(sk)->icsk_timeout, (jiffies + delay)))
return false;
- inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, delay, TCP_RTO_MAX);
- tp->early_retrans_delayed = 1;
+ inet_csk_reset_xmit_timer(sk, ICSK_TIME_EARLY_RETRANS, delay,
+ TCP_RTO_MAX);
return true;
}
* interval if appropriate.
*/
if (tp->do_early_retrans && !tp->retrans_out && tp->sacked_out &&
- (tp->packets_out == (tp->sacked_out + 1) && tp->packets_out < 4) &&
+ (tp->packets_out >= (tp->sacked_out + 1) && tp->packets_out < 4) &&
!tcp_may_send_now(sk))
return !tcp_pause_early_retransmit(sk, flag);
*/
void tcp_rearm_rto(struct sock *sk)
{
+ const struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
/* If the retrans timer is currently being used by Fast Open
} else {
u32 rto = inet_csk(sk)->icsk_rto;
/* Offset the time elapsed after installing regular RTO */
- if (tp->early_retrans_delayed) {
+ if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
+ icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
struct sk_buff *skb = tcp_write_queue_head(sk);
const u32 rto_time_stamp = TCP_SKB_CB(skb)->when + rto;
s32 delta = (s32)(rto_time_stamp - tcp_time_stamp);
/* delta may not be positive if the socket is locked
- * when the delayed ER timer fires and is rescheduled.
+ * when the retrans timer fires and is rescheduled.
*/
if (delta > 0)
rto = delta;
inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
TCP_RTO_MAX);
}
- tp->early_retrans_delayed = 0;
}
/* This function is called when the delayed ER timer fires. TCP enters
if (after(ack, tp->snd_nxt))
goto invalid_ack;
- if (tp->early_retrans_delayed)
+ if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
+ icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)
tcp_rearm_rto(sk);
if (after(ack, prior_snd_una))
if (dst)
dst_confirm(dst);
}
+
+ if (icsk->icsk_pending == ICSK_TIME_RETRANS)
+ tcp_schedule_loss_probe(sk);
return 1;
no_queue:
__u16 srcp = ntohs(inet->inet_sport);
int rx_queue;
- if (icsk->icsk_pending == ICSK_TIME_RETRANS) {
+ if (icsk->icsk_pending == ICSK_TIME_RETRANS ||
+ icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
+ icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
timer_active = 1;
timer_expires = icsk->icsk_timeout;
} else if (icsk->icsk_pending == ICSK_TIME_PROBE0) {
/* Account for new data that has been sent to the network. */
static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
{
+ struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
unsigned int prior_packets = tp->packets_out;
tp->frto_counter = 3;
tp->packets_out += tcp_skb_pcount(skb);
- if (!prior_packets || tp->early_retrans_delayed)
+ if (!prior_packets || icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
+ icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)
tcp_rearm_rto(sk);
}
* snd_up-64k-mss .. snd_up cannot be large. However, taking into
* account rare use of URG, this is not a big flaw.
*
+ * Send at most one packet when push_one > 0. Temporarily ignore
+ * cwnd limit to force at most one packet out when push_one == 2.
+
* Returns true, if no segments are in flight and we have queued segments,
* but cannot send anything now because of SWS or another problem.
*/
goto repair; /* Skip network transmission */
cwnd_quota = tcp_cwnd_test(tp, skb);
- if (!cwnd_quota)
- break;
+ if (!cwnd_quota) {
+ if (push_one == 2)
+ /* Force out a loss probe pkt. */
+ cwnd_quota = 1;
+ else
+ break;
+ }
if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
break;
if (likely(sent_pkts)) {
if (tcp_in_cwnd_reduction(sk))
tp->prr_out += sent_pkts;
+
+ /* Send one loss probe per tail loss episode. */
+ if (push_one != 2)
+ tcp_schedule_loss_probe(sk);
tcp_cwnd_validate(sk);
return false;
}
- return !tp->packets_out && tcp_send_head(sk);
+ return (push_one == 2) || (!tp->packets_out && tcp_send_head(sk));
+}
+
+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 = tp->srtt >> 3;
+
+ if (WARN_ON(icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS))
+ return false;
+ /* 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 (sk->sk_state == TCP_SYN_RECV)
+ 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.
+ */
+ if (sysctl_tcp_early_retrans < 3 || !rtt || !tp->packets_out ||
+ !tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
+ return false;
+
+ if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) &&
+ tcp_send_head(sk))
+ return false;
+
+ /* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account
+ * for delayed ack when there's one outstanding packet.
+ */
+ timeout = rtt << 1;
+ if (tp->packets_out == 1)
+ timeout = max_t(u32, timeout,
+ (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_time_stamp + 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_time_stamp;
+ if (delta > 0)
+ timeout = delta;
+ }
+
+ inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,
+ TCP_RTO_MAX);
+ return true;
+}
+
+/* When probe timeout (PTO) fires, send a new segment if one exists, else
+ * retransmit the last segment.
+ */
+void tcp_send_loss_probe(struct sock *sk)
+{
+ struct sk_buff *skb;
+ int pcount;
+ int mss = tcp_current_mss(sk);
+ int err = -1;
+
+ if (tcp_send_head(sk) != NULL) {
+ err = tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
+ goto rearm_timer;
+ }
+
+ /* Retransmit last segment. */
+ skb = tcp_write_queue_tail(sk);
+ if (WARN_ON(!skb))
+ goto rearm_timer;
+
+ pcount = tcp_skb_pcount(skb);
+ if (WARN_ON(!pcount))
+ goto rearm_timer;
+
+ if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
+ if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss)))
+ goto rearm_timer;
+ skb = tcp_write_queue_tail(sk);
+ }
+
+ if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
+ goto rearm_timer;
+
+ /* Probe with zero data doesn't trigger fast recovery. */
+ if (skb->len > 0)
+ err = __tcp_retransmit_skb(sk, skb);
+
+rearm_timer:
+ inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
+ inet_csk(sk)->icsk_rto,
+ TCP_RTO_MAX);
+
+ if (likely(!err))
+ NET_INC_STATS_BH(sock_net(sk),
+ LINUX_MIB_TCPLOSSPROBES);
+ return;
}
/* Push out any pending frames which were held back due to
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
- if (tp->early_retrans_delayed) {
- tcp_resume_early_retransmit(sk);
- return;
- }
if (tp->fastopen_rsk) {
WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
sk->sk_state != TCP_FIN_WAIT1);
}
event = icsk->icsk_pending;
- icsk->icsk_pending = 0;
switch (event) {
+ case ICSK_TIME_EARLY_RETRANS:
+ tcp_resume_early_retransmit(sk);
+ break;
+ case ICSK_TIME_LOSS_PROBE:
+ tcp_send_loss_probe(sk);
+ break;
case ICSK_TIME_RETRANS:
+ icsk->icsk_pending = 0;
tcp_retransmit_timer(sk);
break;
case ICSK_TIME_PROBE0:
+ icsk->icsk_pending = 0;
tcp_probe_timer(sk);
break;
}
projects / ~andy / linux / commitdiff