]> git.saurik.com Git - apple/xnu.git/blobdiff - bsd/netinet/tcp_timer.c
xnu-2782.30.5.tar.gz
[apple/xnu.git] / bsd / netinet / tcp_timer.c
index b1ac3138b186b3b102ab02419ae4442d0c95eff5..aa2317164e82fc8f0e50e31efcc4526f88dda69f 100644 (file)
@@ -79,6 +79,7 @@
 
 #include <net/route.h>
 #include <net/if_var.h>
+#include <net/ntstat.h>
 
 #include <netinet/in.h>
 #include <netinet/in_systm.h>
 #include <mach/sdt.h>
 #include <netinet/mptcp_var.h>
 
-extern void postevent(struct socket *, struct sockbuf *,
-                                               int);
-#define DBG_FNC_TCP_FAST       NETDBG_CODE(DBG_NETTCP, (5 << 8))
-#define DBG_FNC_TCP_SLOW       NETDBG_CODE(DBG_NETTCP, (5 << 8) | 1)
-
 #define TIMERENTRY_TO_TP(te) ((struct tcpcb *)((uintptr_t)te - offsetof(struct tcpcb, tentry.le.le_next))) 
 
 #define VERIFY_NEXT_LINK(elm,field) do {       \
@@ -123,16 +119,24 @@ extern void postevent(struct socket *, struct sockbuf *,
                panic("Bad link elm %p prev->next != elm", (elm));      \
 } while(0)
 
+#define TCP_SET_TIMER_MODE(mode, i) do { \
+       if (IS_TIMER_HZ_10MS(i)) \
+               (mode) |= TCP_TIMERLIST_10MS_MODE; \
+       else if (IS_TIMER_HZ_100MS(i)) \
+               (mode) |= TCP_TIMERLIST_100MS_MODE; \
+       else \
+               (mode) |= TCP_TIMERLIST_500MS_MODE; \
+} while(0)
+
+/* Max number of times a stretch ack can be delayed on a connection */
+#define        TCP_STRETCHACK_DELAY_THRESHOLD  5
+
 /* tcp timer list */
 struct tcptimerlist tcp_timer_list;
 
 /* List of pcbs in timewait state, protected by tcbinfo's ipi_lock */
 struct tcptailq tcp_tw_tailq;
 
-static int     background_io_trigger = 5;
-SYSCTL_INT(_net_inet_tcp, OID_AUTO, background_io_trigger, CTLFLAG_RW | CTLFLAG_LOCKED,
-    &background_io_trigger, 0, "Background IO Trigger Setting");
-
 static int
 sysctl_msec_to_ticks SYSCTL_HANDLER_ARGS
 {
@@ -155,45 +159,59 @@ sysctl_msec_to_ticks SYSCTL_HANDLER_ARGS
 }
 
 int    tcp_keepinit;
-SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINIT, keepinit, CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED,
+SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINIT, keepinit,
+    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED,
     &tcp_keepinit, 0, sysctl_msec_to_ticks, "I", "");
 
 int    tcp_keepidle;
-SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPIDLE, keepidle, CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED,
+SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPIDLE, keepidle,
+    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED,
     &tcp_keepidle, 0, sysctl_msec_to_ticks, "I", "");
 
 int    tcp_keepintvl;
-SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINTVL, keepintvl, CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED,
+SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINTVL, keepintvl,
+    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED,
     &tcp_keepintvl, 0, sysctl_msec_to_ticks, "I", "");
 
 int    tcp_keepcnt;
-SYSCTL_INT(_net_inet_tcp, OID_AUTO, keepcnt, CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED,
-       &tcp_keepcnt, 0, "number of times to repeat keepalive");
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, keepcnt,
+    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED,
+    &tcp_keepcnt, 0, "number of times to repeat keepalive");
 
 int    tcp_msl;
-SYSCTL_PROC(_net_inet_tcp, OID_AUTO, msl, CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED,
+SYSCTL_PROC(_net_inet_tcp, OID_AUTO, msl,
+    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED,
     &tcp_msl, 0, sysctl_msec_to_ticks, "I", "Maximum segment lifetime");
 
 /* 
- * Avoid DoS via TCP Robustness in Persist Condition (see http://www.ietf.org/id/draft-ananth-tcpm-persist-02.txt)
- * by allowing a system wide maximum persistence timeout value when in Zero Window Probe mode.
- * Expressed in milliseconds to be consistent without timeout related values, the TCP socket option is in seconds.
+ * Avoid DoS via TCP Robustness in Persist Condition
+ * (see http://www.ietf.org/id/draft-ananth-tcpm-persist-02.txt)
+ * by allowing a system wide maximum persistence timeout value when in
+ * Zero Window Probe mode.
+ *
+ * Expressed in milliseconds to be consistent without timeout related
+ * values, the TCP socket option is in seconds.
  */
 u_int32_t tcp_max_persist_timeout = 0;
-SYSCTL_PROC(_net_inet_tcp, OID_AUTO, max_persist_timeout, CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED,
-    &tcp_max_persist_timeout, 0, sysctl_msec_to_ticks, "I", "Maximum persistence timout for ZWP");
+SYSCTL_PROC(_net_inet_tcp, OID_AUTO, max_persist_timeout,
+    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED,
+    &tcp_max_persist_timeout, 0, sysctl_msec_to_ticks, "I", 
+    "Maximum persistence timeout for ZWP");
 
 static int     always_keepalive = 0;
-SYSCTL_INT(_net_inet_tcp, OID_AUTO, always_keepalive, CTLFLAG_RW | CTLFLAG_LOCKED,
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, always_keepalive,
+    CTLFLAG_RW | CTLFLAG_LOCKED,
     &always_keepalive , 0, "Assume SO_KEEPALIVE on all TCP connections");
 
-/* This parameter determines how long the timer list will stay in fast mode even
- * though all connections are idle. In fast mode, the timer will fire more frequently
- * anticipating new data.
+/*
+ * This parameter determines how long the timer list will stay in fast or
+ * quick mode even though all connections are idle. In this state, the 
+ * timer will run more frequently anticipating new data.
  */
-int timer_fastmode_idlemax = TCP_FASTMODE_IDLEGEN_MAX;
-SYSCTL_INT(_net_inet_tcp, OID_AUTO, timer_fastmode_idlemax, CTLFLAG_RW | CTLFLAG_LOCKED,
-       &timer_fastmode_idlemax, 0, "Maximum idle generations in fast mode");
+int timer_fastmode_idlemax = TCP_FASTMODE_IDLERUN_MAX;
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, timer_fastmode_idlemax,
+    CTLFLAG_RW | CTLFLAG_LOCKED,
+    &timer_fastmode_idlemax, 0, "Maximum idle generations in fast mode");
 
 /*
  * See tcp_syn_backoff[] for interval values between SYN retransmits;
@@ -203,42 +221,49 @@ SYSCTL_INT(_net_inet_tcp, OID_AUTO, timer_fastmode_idlemax, CTLFLAG_RW | CTLFLAG
  * two options.
  */
 static int tcp_broken_peer_syn_rxmit_thres = 7;
-SYSCTL_INT(_net_inet_tcp, OID_AUTO, broken_peer_syn_rxmit_thres, CTLFLAG_RW | CTLFLAG_LOCKED,
-    &tcp_broken_peer_syn_rxmit_thres, 0, "Number of retransmitted SYNs before "
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, broken_peer_syn_rxmit_thres,
+    CTLFLAG_RW | CTLFLAG_LOCKED,
+    &tcp_broken_peer_syn_rxmit_thres, 0, 
+    "Number of retransmitted SYNs before "
     "TCP disables rfc1323 and rfc1644 during the rest of attempts");
 
 /* A higher threshold on local connections for disabling RFC 1323 options */
 static int tcp_broken_peer_syn_rxmit_thres_local = 10;
 SYSCTL_INT(_net_inet_tcp, OID_AUTO, broken_peer_syn_rexmit_thres_local, 
-       CTLFLAG_RW | CTLFLAG_LOCKED, &tcp_broken_peer_syn_rxmit_thres_local, 0,
-       "Number of retransmitted SYNs before disabling RFC 1323 options on local connections");
+    CTLFLAG_RW | CTLFLAG_LOCKED, &tcp_broken_peer_syn_rxmit_thres_local, 0,
+    "Number of retransmitted SYNs before disabling RFC 1323 "
+    "options on local connections");
 
 static int tcp_timer_advanced = 0;
-SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcp_timer_advanced, CTLFLAG_RD | CTLFLAG_LOCKED,
-    &tcp_timer_advanced, 0, "Number of times one of the timers was advanced");
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcp_timer_advanced,
+    CTLFLAG_RD | CTLFLAG_LOCKED, &tcp_timer_advanced, 0,
+    "Number of times one of the timers was advanced");
 
 static int tcp_resched_timerlist = 0;
-SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcp_resched_timerlist, CTLFLAG_RD | CTLFLAG_LOCKED,
-    &tcp_resched_timerlist, 0, 
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcp_resched_timerlist,
+    CTLFLAG_RD | CTLFLAG_LOCKED, &tcp_resched_timerlist, 0, 
     "Number of times timer list was rescheduled as part of processing a packet");
 
 int    tcp_pmtud_black_hole_detect = 1 ;
-SYSCTL_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_detection, CTLFLAG_RW | CTLFLAG_LOCKED,
-    &tcp_pmtud_black_hole_detect, 0, "Path MTU Discovery Black Hole Detection");
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_detection,
+    CTLFLAG_RW | CTLFLAG_LOCKED, &tcp_pmtud_black_hole_detect, 0,
+    "Path MTU Discovery Black Hole Detection");
 
 int    tcp_pmtud_black_hole_mss = 1200 ;
-SYSCTL_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_mss, CTLFLAG_RW | CTLFLAG_LOCKED,
-    &tcp_pmtud_black_hole_mss, 0, "Path MTU Discovery Black Hole Detection lowered MSS");
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_mss,
+    CTLFLAG_RW | CTLFLAG_LOCKED, &tcp_pmtud_black_hole_mss, 0,
+    "Path MTU Discovery Black Hole Detection lowered MSS");
 
 /* performed garbage collection of "used" sockets */
 static boolean_t tcp_gc_done = FALSE;
 
-       /* max idle probes */
+/* max idle probes */
 int    tcp_maxpersistidle;
 
-/* TCP delack timer is set to 100 ms. Since the processing of timer list in fast
- * mode will happen no faster than 100 ms, the delayed ack timer will fire some where 
- * between 100 and 200 ms.
+/*
+ * TCP delack timer is set to 100 ms. Since the processing of timer list
+ * in fast mode will happen no faster than 100 ms, the delayed ack timer
+ * will fire some where between 100 and 200 ms.
  */
 int    tcp_delack = TCP_RETRANSHZ / 10;
 
@@ -249,45 +274,37 @@ int       tcp_delack = TCP_RETRANSHZ / 10;
 int    tcp_jack_rxmt = TCP_RETRANSHZ / 2;
 #endif /* MPTCP */
 
-/* The frequency of running through the TCP timer list in 
- * fast and slow mode can be configured.
- */
-SYSCTL_UINT(_net_inet_tcp, OID_AUTO, timer_fastquantum, CTLFLAG_RW | CTLFLAG_LOCKED,
-       &tcp_timer_list.fast_quantum, TCP_FASTTIMER_QUANTUM, 
-       "Frequency of running timer list in fast mode");
-
-SYSCTL_UINT(_net_inet_tcp, OID_AUTO, timer_slowquantum, CTLFLAG_RW | CTLFLAG_LOCKED,
-       &tcp_timer_list.slow_quantum, TCP_SLOWTIMER_QUANTUM, 
-       "Frequency of running timer list in slow mode");
-
 static void tcp_remove_timer(struct tcpcb *tp);
 static void tcp_sched_timerlist(uint32_t offset);
-static uint32_t tcp_run_conn_timer(struct tcpcb *tp, uint16_t *next_index);
+static u_int32_t tcp_run_conn_timer(struct tcpcb *tp, u_int16_t *mode);
 static void tcp_sched_timers(struct tcpcb *tp);
 static inline void tcp_set_lotimer_index(struct tcpcb *);
 static void tcp_rexmt_save_state(struct tcpcb *tp);
-void tcp_remove_from_time_wait(struct inpcb *inp);
+__private_extern__ void tcp_remove_from_time_wait(struct inpcb *inp);
+__private_extern__ void tcp_report_stats(void);
 
-/* Macro to compare two timers. If there is a reset of the sign bit, it is 
- * safe to assume that the timer has wrapped around. By doing signed comparision, 
- * we take care of wrap around such that the value with the sign bit reset is 
- * actually ahead of the other.
+/*
+ * Macro to compare two timers. If there is a reset of the sign bit, 
+ * it is safe to assume that the timer has wrapped around. By doing 
+ * signed comparision, we take care of wrap around such that the value 
+ * with the sign bit reset is actually ahead of the other.
  */
-
-static inline int32_t
+inline int32_t
 timer_diff(uint32_t t1, uint32_t toff1, uint32_t t2, uint32_t toff2) { 
        return (int32_t)((t1 + toff1) - (t2 + toff2));
 };
 
+static u_int64_t tcp_last_report_time;
+#define        TCP_REPORT_STATS_INTERVAL       345600 /* 4 days, in seconds */
+
 /* Returns true if the timer is on the timer list */
 #define TIMER_IS_ON_LIST(tp) ((tp)->t_flags & TF_TIMER_ONLIST)
 
 /* Run the TCP timerlist atleast once every hour */
-#define        TCP_TIMERLIST_MAX_OFFSET        (60 * 60 * TCP_RETRANSHZ)
+#define TCP_TIMERLIST_MAX_OFFSET (60 * 60 * TCP_RETRANSHZ)
 
-static void add_to_time_wait_locked(struct tcpcb *tp, uint32_t delay);
-void   add_to_time_wait(struct tcpcb *tp, uint32_t delay) ;
 
+static void add_to_time_wait_locked(struct tcpcb *tp, uint32_t delay);
 static boolean_t tcp_garbage_collect(struct inpcb *, int);
 
 /*
@@ -330,6 +347,8 @@ void
 add_to_time_wait(struct tcpcb *tp, uint32_t delay)
 {
        struct inpcbinfo *pcbinfo = &tcbinfo;
+       if (tp->t_inpcb->inp_socket->so_options & SO_NOWAKEFROMSLEEP)
+               socket_post_kev_msg_closed(tp->t_inpcb->inp_socket);
 
        if (!lck_rw_try_lock_exclusive(pcbinfo->ipi_lock)) {
                tcp_unlock(tp->t_inpcb->inp_socket, 0, 0);
@@ -608,6 +627,30 @@ static void tcp_rexmt_save_state(struct tcpcb *tp)
        tp->t_flagsext &= ~(TF_RECOMPUTE_RTT);
 }
 
+/*
+ * Revert to the older segment size if there is an indication that PMTU
+ * blackhole detection was not needed.
+ */
+void tcp_pmtud_revert_segment_size(struct tcpcb *tp)
+{
+       int32_t optlen;
+
+       VERIFY(tp->t_pmtud_saved_maxopd > 0);
+       tp->t_flags |= TF_PMTUD; 
+       tp->t_flags &= ~TF_BLACKHOLE; 
+       optlen = tp->t_maxopd - tp->t_maxseg;
+       tp->t_maxopd = tp->t_pmtud_saved_maxopd;
+       tp->t_maxseg = tp->t_maxopd - optlen;
+       /*
+        * Reset the slow-start flight size as it 
+        * may depend on the new MSS
+        */
+       if (CC_ALGO(tp)->cwnd_init != NULL)
+               CC_ALGO(tp)->cwnd_init(tp);
+       tp->t_pmtud_start_ts = 0;
+       tcpstat.tcps_pmtudbh_reverted++;
+}
+
 /*
  * TCP timer processing.
  */
@@ -616,12 +659,9 @@ tcp_timers(tp, timer)
        register struct tcpcb *tp;
        int timer;
 {
-       register int rexmt;
+       int32_t rexmt, optlen = 0, idle_time = 0;
        struct socket *so;
        struct tcptemp *t_template;
-       int optlen = 0;
-       int idle_time = 0;
-
 #if TCPDEBUG
        int ostate;
 #endif
@@ -662,20 +702,24 @@ tcp_timers(tp, timer)
         * to a longer retransmit interval and retransmit one segment.
         */
        case TCPT_REXMT:
-               /* Drop a connection in the retransmit timer
-                * 1. If we have retransmitted more than TCP_MAXRXTSHIFT times
-                * 2. If the time spent in this retransmission episode is more than
-                *    the time limit set with TCP_RXT_CONNDROPTIME socket option
-                * 3. If TCP_RXT_FINDROP socket option was set and we have already
-                *    retransmitted the FIN 3 times without receiving an ack
+               /*
+                * Drop a connection in the retransmit timer
+                * 1. If we have retransmitted more than TCP_MAXRXTSHIFT
+                * times
+                * 2. If the time spent in this retransmission episode is
+                * more than the time limit set with TCP_RXT_CONNDROPTIME
+                * socket option
+                * 3. If TCP_RXT_FINDROP socket option was set and
+                * we have already retransmitted the FIN 3 times without
+                * receiving an ack
                 */
                if (++tp->t_rxtshift > TCP_MAXRXTSHIFT ||
-                       (tp->t_rxt_conndroptime > 0 && tp->t_rxtstart > 0 && 
-                       (tcp_now - tp->t_rxtstart) >= tp->t_rxt_conndroptime) ||
-                       ((tp->t_flagsext & TF_RXTFINDROP) != 0 &&
+                   (tp->t_rxt_conndroptime > 0 
+                   && tp->t_rxtstart > 0 && 
+                   (tcp_now - tp->t_rxtstart) >= tp->t_rxt_conndroptime)
+                   || ((tp->t_flagsext & TF_RXTFINDROP) != 0 &&
                        (tp->t_flags & TF_SENTFIN) != 0 &&
                        tp->t_rxtshift >= 4)) {
-
                        if ((tp->t_flagsext & TF_RXTFINDROP) != 0) {
                                tcpstat.tcps_rxtfindrop++;
                        } else {
@@ -706,7 +750,7 @@ tcp_timers(tp, timer)
                        tcp_rexmt_save_state(tp);
                }
 #if MPTCP
-               if ((tp->t_rxtshift == mptcp_fail_thresh) &&
+               if ((tp->t_rxtshift >= mptcp_fail_thresh) &&
                    (tp->t_state == TCPS_ESTABLISHED) &&
                    (tp->t_mpflags & TMPF_MPTCP_TRUE)) {
                        mptcp_act_on_txfail(so);
@@ -723,12 +767,34 @@ tcp_timers(tp, timer)
                                SO_FILT_HINT_ADAPTIVE_WTIMO));
                }
 
+               /*
+                * If this is a retransmit timeout after PTO, the PTO
+                * was not effective
+                */
+               if (tp->t_flagsext & TF_SENT_TLPROBE) {
+                       tp->t_flagsext &= ~(TF_SENT_TLPROBE);
+                       tcpstat.tcps_rto_after_pto++;
+               }
+
+               if (tp->t_flagsext & TF_DELAY_RECOVERY) {
+                       /*
+                        * Retransmit timer fired before entering recovery
+                        * on a connection with packet re-ordering. This
+                        * suggests that the reordering metrics computed
+                        * are not accurate.
+                        */
+                       tp->t_reorderwin = 0;
+                       tp->t_timer[TCPT_DELAYFR] = 0;
+                       tp->t_flagsext &= ~(TF_DELAY_RECOVERY);
+               }
+
                if (tp->t_state == TCPS_SYN_SENT) {
                        rexmt = TCP_REXMTVAL(tp) * tcp_syn_backoff[tp->t_rxtshift];
                        tp->t_stat.synrxtshift = tp->t_rxtshift;
-               }
-               else
+               } else {
                        rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
+               }
+
                TCPT_RANGESET(tp->t_rxtcur, rexmt,
                        tp->t_rttmin, TCPTV_REXMTMAX, 
                        TCP_ADD_REXMTSLOP(tp));
@@ -739,16 +805,19 @@ tcp_timers(tp, timer)
 
                tcp_free_sackholes(tp);
                /*
-                * Check for potential Path MTU Discovery Black Hole 
+                * Check for potential Path MTU Discovery Black Hole
                 */
-
-               if (tcp_pmtud_black_hole_detect && (tp->t_state == TCPS_ESTABLISHED)) {
-                       if (((tp->t_flags & (TF_PMTUD|TF_MAXSEGSNT)) == (TF_PMTUD|TF_MAXSEGSNT)) &&
+               if (tcp_pmtud_black_hole_detect &&
+                       !(tp->t_flagsext & TF_NOBLACKHOLE_DETECTION) &&
+                       (tp->t_state == TCPS_ESTABLISHED)) {
+                       if (((tp->t_flags & (TF_PMTUD|TF_MAXSEGSNT))
+                           == (TF_PMTUD|TF_MAXSEGSNT)) &&
                                 (tp->t_rxtshift == 2)) {
                                /* 
                                 * Enter Path MTU Black-hole Detection mechanism:
                                 * - Disable Path MTU Discovery (IP "DF" bit).
-                                * - Reduce MTU to lower value than what we negociated with peer.
+                                * - Reduce MTU to lower value than what we
+                                * negotiated with the peer.
                                 */
                                /* Disable Path MTU Discovery for now */
                                tp->t_flags &= ~TF_PMTUD;
@@ -757,6 +826,9 @@ tcp_timers(tp, timer)
                                optlen = tp->t_maxopd - tp->t_maxseg;
                                /* Keep track of previous MSS */
                                tp->t_pmtud_saved_maxopd = tp->t_maxopd;
+                               tp->t_pmtud_start_ts = tcp_now;
+                               if (tp->t_pmtud_start_ts == 0)
+                                       tp->t_pmtud_start_ts++;
                                /* Reduce the MSS to intermediary value */
                                if (tp->t_maxopd > tcp_pmtud_black_hole_mss) {
                                        tp->t_maxopd = tcp_pmtud_black_hole_mss;
@@ -777,35 +849,28 @@ tcp_timers(tp, timer)
                                        CC_ALGO(tp)->cwnd_init(tp);
                        }
                        /*
-                        * If further retransmissions are still unsuccessful with a lowered MTU,
-                        * maybe this isn't a Black Hole and we restore the previous MSS and
-                        * blackhole detection flags.
+                        * If further retransmissions are still
+                        * unsuccessful with a lowered MTU, maybe this
+                        * isn't a Black Hole and we restore the previous
+                        * MSS and blackhole detection flags.
                         */
                        else {
        
-                               if ((tp->t_flags & TF_BLACKHOLE) && (tp->t_rxtshift > 4)) {
-                                       tp->t_flags |= TF_PMTUD; 
-                                       tp->t_flags &= ~TF_BLACKHOLE; 
-                                       optlen = tp->t_maxopd - tp->t_maxseg;
-                                       tp->t_maxopd = tp->t_pmtud_saved_maxopd;
-                                       tp->t_maxseg = tp->t_maxopd - optlen;
-                                       /*
-                                        * Reset the slow-start flight size as it 
-                                        * may depend on the new MSS
-                                        */
-                                       if (CC_ALGO(tp)->cwnd_init != NULL)
-                                               CC_ALGO(tp)->cwnd_init(tp);
+                               if ((tp->t_flags & TF_BLACKHOLE) &&
+                                   (tp->t_rxtshift > 4)) {
+                                       tcp_pmtud_revert_segment_size(tp);
                                }
                        }
                }
 
 
                /*
-                * Disable rfc1323 and rfc1644 if we haven't got any response to
-                * our SYN (after we reach the threshold) to work-around some
-                * broken terminal servers (most of which have hopefully been
-                * retired) that have bad VJ header compression code which
-                * trashes TCP segments containing unknown-to-them TCP options.
+                * Disable rfc1323 and rfc1644 if we haven't got any
+                * response to our SYN (after we reach the threshold)
+                * to work-around some broken terminal servers (most of
+                * which have hopefully been retired) that have bad VJ
+                * header compression code which trashes TCP segments
+                * containing unknown-to-them TCP options.
                 * Do this only on non-local connections.
                 */
                if (tp->t_state == TCPS_SYN_SENT &&
@@ -843,14 +908,16 @@ tcp_timers(tp, timer)
                 * Force a segment to be sent.
                 */
                tp->t_flags |= TF_ACKNOW;
-               /*
-                * If timing a segment in this window, stop the timer.
-                */
+
+               /* If timing a segment in this window, stop the timer */
                tp->t_rtttime = 0;
 
-               EXIT_FASTRECOVERY(tp);
+               if (!IN_FASTRECOVERY(tp) && tp->t_rxtshift == 1)
+                       tcpstat.tcps_tailloss_rto++;
+
 
-               /* RFC 5681 says: when a TCP sender detects segment loss
+               /*
+                * RFC 5681 says: when a TCP sender detects segment loss
                 * using retransmit timer and the given segment has already
                 * been retransmitted by way of the retransmission timer at
                 * least once, the value of ssthresh is held constant
@@ -859,6 +926,7 @@ tcp_timers(tp, timer)
                        CC_ALGO(tp)->after_timeout != NULL)
                        CC_ALGO(tp)->after_timeout(tp);
 
+               EXIT_FASTRECOVERY(tp);
 
                /* CWR notifications are to be sent on new data right after
                 * RTOs, Fast Retransmits and ECE notification receipts.
@@ -867,9 +935,7 @@ tcp_timers(tp, timer)
                        tp->ecn_flags |= TE_SENDCWR;
                }
 fc_output:
-               DTRACE_TCP5(cc, void, NULL, struct inpcb *, tp->t_inpcb,
-                       struct tcpcb *, tp, struct tcphdr *, NULL,
-                       int32_t, TCP_CC_REXMT_TIMEOUT);
+               tcp_ccdbg_trace(tp, NULL, TCP_CC_REXMT_TIMEOUT);
 
                (void) tcp_output(tp);
                break;
@@ -904,9 +970,9 @@ fc_output:
                        break;
                }
                tcp_setpersist(tp);
-               tp->t_force = 1;
+               tp->t_flagsext |= TF_FORCE;
                (void) tcp_output(tp);
-               tp->t_force = 0;
+               tp->t_flagsext &= ~TF_FORCE;
                break;
 
        /*
@@ -921,8 +987,8 @@ fc_output:
                 * MPTCP must not also, after sending Data FINs.
                 */
                struct mptcb *mp_tp = tp->t_mptcb;
-               if ((tp->t_mpflags & TMPF_MPTCP_TRUE) && 
-                   (mp_tp == NULL)) {
+               if ((tp->t_mpflags & TMPF_MPTCP_TRUE) &&
+                   (tp->t_state > TCPS_ESTABLISHED)) {
                        goto dropit;
                } else if (mp_tp != NULL) {
                        if ((mptcp_ok_to_keepalive(mp_tp) == 0))
@@ -952,24 +1018,20 @@ fc_output:
                        tcpstat.tcps_keepprobe++;
                        t_template = tcp_maketemplate(tp);
                        if (t_template) {
-                               unsigned int ifscope, nocell = 0;
+                               struct inpcb *inp = tp->t_inpcb;
+                               struct tcp_respond_args tra;
 
+                               bzero(&tra, sizeof(tra));
+                               tra.nocell = INP_NO_CELLULAR(inp);
+                               tra.noexpensive = INP_NO_EXPENSIVE(inp);
+                               tra.awdl_unrestricted = INP_AWDL_UNRESTRICTED(inp);
                                if (tp->t_inpcb->inp_flags & INP_BOUND_IF)
-                                       ifscope = tp->t_inpcb->inp_boundifp->if_index;
+                                       tra.ifscope = tp->t_inpcb->inp_boundifp->if_index;
                                else
-                                       ifscope = IFSCOPE_NONE;
-
-                               /*
-                                * If the socket isn't allowed to use the
-                                * cellular interface, indicate it as such.
-                                */
-                               if (tp->t_inpcb->inp_flags & INP_NO_IFT_CELLULAR)
-                                       nocell = 1;
-
+                                       tra.ifscope = IFSCOPE_NONE;
                                tcp_respond(tp, t_template->tt_ipgen,
                                    &t_template->tt_t, (struct mbuf *)NULL,
-                                   tp->rcv_nxt, tp->snd_una - 1, 0, ifscope,
-                                   nocell);
+                                   tp->rcv_nxt, tp->snd_una - 1, 0, &tra);
                                (void) m_free(dtom(t_template));
                                if (tp->t_flagsext & TF_DETECT_READSTALL)
                                        tp->t_rtimo_probes++;
@@ -1006,16 +1068,39 @@ fc_output:
                        tp->t_timer[TCPT_DELACK] = 0;
                        tp->t_flags |= TF_ACKNOW;
 
-                       /* If delayed ack timer fired while stretching acks
-                        * go back to acking every other packet
+                       /*
+                        * If delayed ack timer fired while stretching
+                        * acks, count the number of times the streaming
+                        * detection was not correct. If this exceeds a 
+                        * threshold, disable strech ack on this
+                        * connection
+                        *
+                        * Also, go back to acking every other packet.
                         */
-                       if ((tp->t_flags & TF_STRETCHACK) != 0)
+                       if ((tp->t_flags & TF_STRETCHACK)) {
+                               if (tp->t_unacksegs > 1 &&
+                                   tp->t_unacksegs < maxseg_unacked)
+                                       tp->t_stretchack_delayed++;
+
+                               if (tp->t_stretchack_delayed >
+                                       TCP_STRETCHACK_DELAY_THRESHOLD) {
+                                       tp->t_flagsext |= TF_DISABLE_STRETCHACK;
+                                       /*
+                                        * Note the time at which stretch
+                                        * ack was disabled automatically
+                                        */
+                                       tp->rcv_nostrack_ts = tcp_now;
+                                       tcpstat.tcps_nostretchack++;
+                                       tp->t_stretchack_delayed = 0;
+                               }
                                tcp_reset_stretch_ack(tp);
+                       }
 
-                       /* If we are measuring inter packet arrival jitter for 
-                        * throttling a connection, this delayed ack might be 
-                        * the reason for accumulating some jitter. So let's
-                        * restart the measurement.
+                       /*
+                        * If we are measuring inter packet arrival jitter
+                        * for throttling a connection, this delayed ack
+                        * might be the reason for accumulating some
+                        * jitter. So let's restart the measurement.
                         */
                        CLEAR_IAJ_STATE(tp);
 
@@ -1051,11 +1136,110 @@ fc_output:
                break;
 #endif /* MPTCP */
 
-#if TCPDEBUG
-       if (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)
-               tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
-                         PRU_SLOWTIMO);
-#endif
+       case TCPT_PTO:
+       {
+               tcp_seq old_snd_nxt;
+               int32_t snd_len;
+               boolean_t rescue_rxt = FALSE;
+
+               tp->t_flagsext &= ~(TF_SENT_TLPROBE);
+
+               /*
+                * Check if the connection is in the right state to
+                * send a probe
+                */
+               if (tp->t_state != TCPS_ESTABLISHED ||
+                   tp->t_rxtshift > 0 || tp->snd_max == tp->snd_una ||
+                   !SACK_ENABLED(tp) || TAILQ_EMPTY(&tp->snd_holes) ||
+                   (IN_FASTRECOVERY(tp) &&
+                   (SEQ_GEQ(tp->snd_fack, tp->snd_recover) ||
+                   SEQ_GT(tp->snd_nxt, tp->sack_newdata))))
+                       break;
+
+               tcpstat.tcps_pto++;
+
+               /* If timing a segment in this window, stop the timer */
+               tp->t_rtttime = 0;
+
+               if (IN_FASTRECOVERY(tp)) {
+                       /*
+                        * Send a probe to detect tail loss in a
+                        * recovery window when the connection is in
+                        * fast_recovery.
+                        */
+                       old_snd_nxt = tp->snd_nxt;
+                       rescue_rxt = TRUE;
+                       VERIFY(SEQ_GEQ(tp->snd_fack, tp->snd_una));
+                       snd_len = min((tp->snd_recover - tp->snd_fack),
+                           tp->t_maxseg);
+                       tp->snd_nxt = tp->snd_recover - snd_len;
+                       tcpstat.tcps_pto_in_recovery++;
+                       tcp_ccdbg_trace(tp, NULL, TCP_CC_TLP_IN_FASTRECOVERY);
+               } else {
+                       /*
+                        * If there is no new data to send or if the
+                        * connection is limited by receive window then
+                        * retransmit the last segment, otherwise send
+                        * new data.
+                        */
+                       snd_len = min(so->so_snd.sb_cc, tp->snd_wnd)
+                           - (tp->snd_max - tp->snd_una);
+                       if (snd_len > 0) {
+                               tp->snd_nxt = tp->snd_max;
+                       } else {
+                               snd_len = min((tp->snd_max - tp->snd_una),
+                                   tp->t_maxseg);
+                               tp->snd_nxt = tp->snd_max - snd_len;
+                       }
+               }
+
+               /* Note that tail loss probe is being sent */
+               tp->t_flagsext |= TF_SENT_TLPROBE;
+               tp->t_tlpstart = tcp_now;
+
+               tp->snd_cwnd += tp->t_maxseg;
+               (void )tcp_output(tp);
+               tp->snd_cwnd -= tp->t_maxseg;
+
+               tp->t_tlphighrxt = tp->snd_nxt;
+
+               /*
+                * If a tail loss probe was sent after entering recovery,
+                * restore the old snd_nxt value so that other packets
+                * will get retransmitted correctly.
+                */
+               if (rescue_rxt)
+                       tp->snd_nxt = old_snd_nxt;
+               break;
+       }
+       case TCPT_DELAYFR:
+               tp->t_flagsext &= ~TF_DELAY_RECOVERY;
+
+               /*
+                * Don't do anything if one of the following is true:
+                * - the connection is already in recovery
+                * - sequence until snd_recover has been acknowledged.
+                * - retransmit timeout has fired
+                */
+               if (IN_FASTRECOVERY(tp) ||
+                   SEQ_GEQ(tp->snd_una, tp->snd_recover) ||
+                   tp->t_rxtshift > 0)
+                       break;
+
+               VERIFY(SACK_ENABLED(tp));
+               if (CC_ALGO(tp)->pre_fr != NULL)
+                       CC_ALGO(tp)->pre_fr(tp);
+               ENTER_FASTRECOVERY(tp);
+               if ((tp->ecn_flags & TE_ECN_ON) == TE_ECN_ON)
+                       tp->ecn_flags |= TE_SENDCWR;
+
+               tp->t_timer[TCPT_REXMT] = 0;
+               tcpstat.tcps_sack_recovery_episode++;
+               tp->sack_newdata = tp->snd_nxt;
+               tp->snd_cwnd = tp->t_maxseg;
+               tcp_ccdbg_trace(tp, NULL, TCP_CC_ENTER_FASTRECOVERY);
+               (void) tcp_output(tp);
+               break;
        dropit:
                tcpstat.tcps_keepdrops++;
                postevent(so, 0, EV_TIMEOUT);
@@ -1064,6 +1248,11 @@ fc_output:
                tp = tcp_drop(tp, ETIMEDOUT);
                break;
        }
+#if TCPDEBUG
+       if (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)
+               tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
+                         PRU_SLOWTIMO);
+#endif
        return (tp);
 }
 
@@ -1098,26 +1287,25 @@ tcp_remove_timer(struct tcpcb *tp)
        lck_mtx_unlock(listp->mtx);
 }
 
-/* Function to check if the timerlist needs to be rescheduled to run
+/*
+ * Function to check if the timerlist needs to be rescheduled to run
  * the timer entry correctly. Basically, this is to check if we can avoid
  * taking the list lock.
  */
 
 static boolean_t
-need_to_resched_timerlist(uint32_t runtime, uint16_t index) {
+need_to_resched_timerlist(u_int32_t runtime, u_int16_t mode)
+{
        struct tcptimerlist *listp = &tcp_timer_list;
        int32_t diff;
-       boolean_t is_fast;
-
-       if (index == TCPT_NONE)
-               return FALSE;
-       is_fast = !(IS_TIMER_SLOW(index));
 
-       /* If the list is being processed then the state of the list is in flux.
-        * In this case always acquire the lock and set the state correctly.
+       /*
+        * If the list is being processed then the state of the list is
+        * in flux. In this case always acquire the lock and set the state
+        * correctly.
         */
        if (listp->running)
-               return TRUE;
+               return (TRUE);
 
        if (!listp->scheduled)
                return (TRUE);
@@ -1125,17 +1313,20 @@ need_to_resched_timerlist(uint32_t runtime, uint16_t index) {
        diff = timer_diff(listp->runtime, 0, runtime, 0);
        if (diff <= 0) {
                /* The list is going to run before this timer */
-               return FALSE;
+               return (FALSE);
        } else {
-               if (is_fast) {
-                       if (diff <= listp->fast_quantum)
-                               return FALSE;
+               if (mode & TCP_TIMERLIST_10MS_MODE) {
+                       if (diff <= TCP_TIMER_10MS_QUANTUM)
+                               return (FALSE);
+               } else if (mode & TCP_TIMERLIST_100MS_MODE) {
+                       if (diff <= TCP_TIMER_100MS_QUANTUM)
+                               return (FALSE);
                } else {
-                       if (diff <= listp->slow_quantum)
-                               return FALSE;
+                       if (diff <= TCP_TIMER_500MS_QUANTUM)
+                               return (FALSE);
                }
        }
-       return TRUE;
+       return (TRUE);
 }
 
 void
@@ -1149,39 +1340,46 @@ tcp_sched_timerlist(uint32_t offset)
 
        offset = min(offset, TCP_TIMERLIST_MAX_OFFSET);
        listp->runtime = tcp_now + offset;
-       if (listp->runtime == 0)
+       if (listp->runtime == 0) {
                listp->runtime++;
+               offset++;
+       }
 
-       clock_interval_to_deadline(offset, NSEC_PER_SEC / TCP_RETRANSHZ,
-               &deadline);
+       clock_interval_to_deadline(offset, USEC_PER_SEC, &deadline);
 
        thread_call_enter_delayed(listp->call, deadline);
        listp->scheduled = TRUE;
 }
 
-/* Function to run the timers for a connection.
+/*
+ * Function to run the timers for a connection.
  *
  * Returns the offset of next timer to be run for this connection which 
  * can be used to reschedule the timerlist.
+ *
+ * te_mode is an out parameter that indicates the modes of active
+ * timers for this connection.
  */
-uint32_t
-tcp_run_conn_timer(struct tcpcb *tp, uint16_t *next_index) {
+u_int32_t
+tcp_run_conn_timer(struct tcpcb *tp, u_int16_t *te_mode) {
 
-        struct socket *so;
-        uint16_t i = 0, index = TCPT_NONE, lo_index = TCPT_NONE;
-        uint32_t timer_val, offset = 0, lo_timer = 0;
+       struct socket *so;
+       u_int16_t i = 0, index = TCPT_NONE, lo_index = TCPT_NONE;
+       u_int32_t timer_val, offset = 0, lo_timer = 0;
        int32_t diff;
        boolean_t needtorun[TCPT_NTIMERS];
        int count = 0;
 
-        VERIFY(tp != NULL);
-        bzero(needtorun, sizeof(needtorun));
+       VERIFY(tp != NULL);
+       bzero(needtorun, sizeof(needtorun));
+       *te_mode = 0;
 
-        tcp_lock(tp->t_inpcb->inp_socket, 1, 0);
+       tcp_lock(tp->t_inpcb->inp_socket, 1, 0);
 
-        so = tp->t_inpcb->inp_socket;
+       so = tp->t_inpcb->inp_socket;
        /* Release the want count on inp */ 
-       if (in_pcb_checkstate(tp->t_inpcb, WNT_RELEASE, 1) == WNT_STOPUSING) {
+       if (in_pcb_checkstate(tp->t_inpcb, WNT_RELEASE, 1)
+               == WNT_STOPUSING) {
                if (TIMER_IS_ON_LIST(tp)) {
                        tcp_remove_timer(tp);
                }
@@ -1192,19 +1390,21 @@ tcp_run_conn_timer(struct tcpcb *tp, uint16_t *next_index) {
                goto done;
        }
 
-        /* Since the timer thread needs to wait for tcp lock, it may race
-         * with another thread that can cancel or reschedule the timer that is
-         * about to run. Check if we need to run anything.
-         */
+       /*
+        * Since the timer thread needs to wait for tcp lock, it may race
+        * with another thread that can cancel or reschedule the timer
+        * that is about to run. Check if we need to run anything.
+        */
        if ((index = tp->tentry.index) == TCPT_NONE)
                goto done;
+       
        timer_val = tp->t_timer[index];
 
        diff = timer_diff(tp->tentry.runtime, 0, tcp_now, 0);
        if (diff > 0) {
                if (tp->tentry.index != TCPT_NONE) {
                        offset = diff;
-                       *(next_index) = tp->tentry.index;
+                       *(te_mode) = tp->tentry.mode;
                }
                goto done;
        }
@@ -1212,18 +1412,20 @@ tcp_run_conn_timer(struct tcpcb *tp, uint16_t *next_index) {
        tp->t_timer[index] = 0;
        if (timer_val > 0) {
                tp = tcp_timers(tp, index);
-               if (tp == NULL) 
+               if (tp == NULL)
                        goto done;
        }
        
-       /* Check if there are any other timers that need to be run. While doing it,
-        * adjust the timer values wrt tcp_now.
+       /*
+        * Check if there are any other timers that need to be run.
+        * While doing it, adjust the timer values wrt tcp_now.
         */
+       tp->tentry.mode = 0;
        for (i = 0; i < TCPT_NTIMERS; ++i) {
                if (tp->t_timer[i] != 0) {
-                       diff = timer_diff(tp->tentry.timer_start, tp->t_timer[i], tcp_now, 0);
+                       diff = timer_diff(tp->tentry.timer_start,
+                               tp->t_timer[i], tcp_now, 0);
                        if (diff <= 0) {
-                               tp->t_timer[i] = 0;
                                needtorun[i] = TRUE;
                                count++;
                        } else {
@@ -1233,27 +1435,31 @@ tcp_run_conn_timer(struct tcpcb *tp, uint16_t *next_index) {
                                        lo_timer = diff;
                                        lo_index = i;
                                }
+                               TCP_SET_TIMER_MODE(tp->tentry.mode, i);
                        }
                }
        }
        
        tp->tentry.timer_start = tcp_now;
        tp->tentry.index = lo_index;
-       if (lo_index != TCPT_NONE) {
-               tp->tentry.runtime = tp->tentry.timer_start + tp->t_timer[lo_index];
+       VERIFY(tp->tentry.index == TCPT_NONE || tp->tentry.mode > 0);
+
+       if (tp->tentry.index != TCPT_NONE) {
+               tp->tentry.runtime = tp->tentry.timer_start +
+                       tp->t_timer[tp->tentry.index];
                if (tp->tentry.runtime == 0)
                        tp->tentry.runtime++;
        }
 
        if (count > 0) {
-               /* run any other timers that are also outstanding at this time. */
+               /* run any other timers outstanding at this time. */
                for (i = 0; i < TCPT_NTIMERS; ++i) {
                        if (needtorun[i]) {
                                tp->t_timer[i] = 0;
                                tp = tcp_timers(tp, i);
                                if (tp == NULL) {
                                        offset = 0;
-                                       *(next_index) = TCPT_NONE;
+                                       *(te_mode) = 0;
                                        goto done;
                                }
                        }
@@ -1263,7 +1469,7 @@ tcp_run_conn_timer(struct tcpcb *tp, uint16_t *next_index) {
 
        if (tp->tentry.index < TCPT_NONE) {
                offset = tp->t_timer[tp->tentry.index];
-               *(next_index) = tp->tentry.index;
+               *(te_mode) = tp->tentry.mode;
        }
 
 done:
@@ -1271,23 +1477,21 @@ done:
                tcp_remove_timer(tp);
                offset = 0;
        }
-        tcp_unlock(so, 1, 0);
-        return offset;
+
+       tcp_unlock(so, 1, 0);
+       return(offset);
 }
 
 void
 tcp_run_timerlist(void * arg1, void * arg2) {
-
 #pragma unused(arg1, arg2)
-       
        struct tcptimerentry *te, *next_te;
        struct tcptimerlist *listp = &tcp_timer_list;
        struct tcpcb *tp;
-       uint32_t next_timer = 0;
-       uint16_t index = TCPT_NONE;
-       boolean_t need_fast = FALSE;
+       uint32_t next_timer = 0; /* offset of the next timer on the list */
+       u_int16_t te_mode = 0;  /* modes of all active timers in a tcpcb */
+       u_int16_t list_mode = 0; /* cumulative of modes of all tcpcbs */
        uint32_t active_count = 0;
-       uint32_t mode = TCP_TIMERLIST_FASTMODE;
 
        calculate_tcp_clock();
 
@@ -1303,19 +1507,24 @@ tcp_run_timerlist(void * arg1, void * arg2) {
                        if (next_timer == 0 || offset < next_timer) {
                                next_timer = offset;
                        }
+                       list_mode |= te->mode;
                        continue;
                }
-               active_count++;
 
                tp = TIMERENTRY_TO_TP(te);
 
-               /* Acquire an inp wantcnt on the inpcb so that the socket won't get
-                * detached even if tcp_close is called
+               /*
+                * Acquire an inp wantcnt on the inpcb so that the socket
+                * won't get detached even if tcp_close is called
                 */
-               if (in_pcb_checkstate(tp->t_inpcb, WNT_ACQUIRE, 0) == WNT_STOPUSING) {
-                       /* Some how this pcb went into dead state while on the timer list,
-                        * just take it off the list. Since the timer list entry pointers 
-                        * are protected by the timer list lock, we can do it here
+               if (in_pcb_checkstate(tp->t_inpcb, WNT_ACQUIRE, 0)
+                   == WNT_STOPUSING) {
+                       /*
+                        * Some how this pcb went into dead state while
+                        * on the timer list, just take it off the list.
+                        * Since the timer list entry pointers are
+                        * protected by the timer list lock, we can 
+                        * do it here without the socket lock.
                         */
                        if (TIMER_IS_ON_LIST(tp)) {
                                tp->t_flags &= ~(TF_TIMER_ONLIST);
@@ -1327,10 +1536,13 @@ tcp_run_timerlist(void * arg1, void * arg2) {
                        }
                        continue;
                }
+               active_count++;
 
-               /* Store the next timerentry pointer before releasing the list lock.
-                * If that entry has to be removed when we release the lock, this
-                * pointer will be updated to the element after that.
+               /*
+                * Store the next timerentry pointer before releasing the
+                * list lock. If that entry has to be removed when we
+                * release the lock, this pointer will be updated to the
+                * element after that.
                 */
                listp->next_te = next_te; 
 
@@ -1339,58 +1551,59 @@ tcp_run_timerlist(void * arg1, void * arg2) {
 
                lck_mtx_unlock(listp->mtx);
 
-               index = TCPT_NONE;
-               offset = tcp_run_conn_timer(tp, &index);
+               offset = tcp_run_conn_timer(tp, &te_mode);
                
                lck_mtx_lock(listp->mtx);
 
                next_te = listp->next_te;
                listp->next_te = NULL;
 
-               if (offset > 0) {
-                       if (index < TCPT_NONE) {
-                               /* Check if this is a fast_timer. */
-                               if (!need_fast && !(IS_TIMER_SLOW(index))) {
-                                       need_fast = TRUE;
-                               }
+               if (offset > 0 && te_mode != 0) {
+                       list_mode |= te_mode;
 
-                               if (next_timer == 0 || offset < next_timer) {
-                                       next_timer = offset;
-                               }
-                       }
+                       if (next_timer == 0 || offset < next_timer)
+                               next_timer = offset;
                }
        }
 
        if (!LIST_EMPTY(&listp->lhead)) {
-               if (listp->mode == TCP_TIMERLIST_FASTMODE) {
-                       if (need_fast || active_count > 0 || 
-                               listp->pref_mode == TCP_TIMERLIST_FASTMODE) {
-                               listp->idlegen = 0;
-                       } else {
-                               listp->idlegen++;
-                               if (listp->idlegen > timer_fastmode_idlemax) {
-                                       mode = TCP_TIMERLIST_SLOWMODE;
-                                       listp->idlegen = 0;
-                               }
-                       }
-               } else {
-                       if (!need_fast) {
-                               mode = TCP_TIMERLIST_SLOWMODE;
-                       }
-               }
+               u_int16_t next_mode = 0;
+               if ((list_mode & TCP_TIMERLIST_10MS_MODE) ||
+                       (listp->pref_mode & TCP_TIMERLIST_10MS_MODE))
+                       next_mode = TCP_TIMERLIST_10MS_MODE;
+               else if ((list_mode & TCP_TIMERLIST_100MS_MODE) ||
+                       (listp->pref_mode & TCP_TIMERLIST_100MS_MODE))
+                       next_mode = TCP_TIMERLIST_100MS_MODE;
+               else
+                       next_mode = TCP_TIMERLIST_500MS_MODE;
 
-               if (mode == TCP_TIMERLIST_FASTMODE || 
-                       listp->pref_mode == TCP_TIMERLIST_FASTMODE) {
-                       next_timer = listp->fast_quantum;
+               if (next_mode != TCP_TIMERLIST_500MS_MODE) {
+                       listp->idleruns = 0;
                } else {
-                       if (listp->pref_offset != 0 && 
-                               listp->pref_offset < next_timer)
-                               next_timer = listp->pref_offset;
-                       if (next_timer < listp->slow_quantum)
-                               next_timer = listp->slow_quantum;
+                       /*
+                        * the next required mode is slow mode, but if
+                        * the last one was a faster mode and we did not
+                        * have enough idle runs, repeat the last mode.
+                        *
+                        * We try to keep the timer list in fast mode for
+                        * some idle time in expectation of new data.
+                        */
+                       if (listp->mode != next_mode &&
+                           listp->idleruns < timer_fastmode_idlemax) {
+                               listp->idleruns++;
+                               next_mode = listp->mode;
+                               next_timer = TCP_TIMER_100MS_QUANTUM;
+                       } else {
+                               listp->idleruns = 0;
+                       }
                }
+               listp->mode = next_mode;
+               if (listp->pref_offset != 0)
+                       next_timer = min(listp->pref_offset, next_timer);
 
-               listp->mode = mode;
+               if (listp->mode == TCP_TIMERLIST_500MS_MODE)
+                       next_timer = max(next_timer,
+                               TCP_TIMER_500MS_QUANTUM);
 
                tcp_sched_timerlist(next_timer);
        } else {
@@ -1408,16 +1621,19 @@ tcp_run_timerlist(void * arg1, void * arg2) {
        lck_mtx_unlock(listp->mtx);
 }
 
-/* Function to verify if a change in timer state is required for a connection */
+/*
+ * Function to check if the timerlist needs to be reschduled to run this
+ * connection's timers correctly.
+ */
 void 
 tcp_sched_timers(struct tcpcb *tp) 
 {
        struct tcptimerentry *te = &tp->tentry;
-       uint16_t index = te->index;
+       u_int16_t index = te->index;
+       u_int16_t mode = te->mode;
        struct tcptimerlist *listp = &tcp_timer_list;
        int32_t offset = 0;
-       boolean_t is_fast;
-       int list_locked = 0;
+       boolean_t list_locked = FALSE;
 
        if (tp->t_inpcb->inp_state == INPCB_STATE_DEAD) {
                /* Just return without adding the dead pcb to the list */
@@ -1428,62 +1644,65 @@ tcp_sched_timers(struct tcpcb *tp)
        }
 
        if (index == TCPT_NONE) {
+               /* Nothing to run */
                tcp_remove_timer(tp);
                return;
        }
 
-       is_fast = !(IS_TIMER_SLOW(index));
+       /*
+        * compute the offset at which the next timer for this connection
+        * has to run.
+        */
        offset = timer_diff(te->runtime, 0, tcp_now, 0);
        if (offset <= 0) {
                offset = 1;
                tcp_timer_advanced++;
        }
-       if (is_fast)
-               offset = listp->fast_quantum;
 
        if (!TIMER_IS_ON_LIST(tp)) {
                if (!list_locked) {
                        lck_mtx_lock(listp->mtx);
-                       list_locked = 1;
+                       list_locked = TRUE;
                }
 
                LIST_INSERT_HEAD(&listp->lhead, te, le);
                tp->t_flags |= TF_TIMER_ONLIST;
 
-               listp->entries++;
-               if (listp->entries > listp->maxentries)
-                       listp->maxentries = listp->entries;
+               listp->entries++;
+               if (listp->entries > listp->maxentries)
+                       listp->maxentries = listp->entries;
 
                /* if the list is not scheduled, just schedule it */
                if (!listp->scheduled)
                        goto schedule;
-
        }
 
 
-       /* timer entry is currently on the list */
-       if (need_to_resched_timerlist(te->runtime, index)) {
+       /*
+        * Timer entry is currently on the list, check if the list needs
+        * to be rescheduled.
+        */
+       if (need_to_resched_timerlist(te->runtime, mode)) {
                tcp_resched_timerlist++;
        
                if (!list_locked) {
                        lck_mtx_lock(listp->mtx);
-                       list_locked = 1;
+                       list_locked = TRUE;
                }
 
                VERIFY_NEXT_LINK(te, le);
                VERIFY_PREV_LINK(te, le);
 
                if (listp->running) {
-                       if (is_fast) {
-                               listp->pref_mode = TCP_TIMERLIST_FASTMODE;
-                       } else if (listp->pref_offset == 0 ||
+                       listp->pref_mode |= mode;
+                       if (listp->pref_offset == 0 ||
                                offset < listp->pref_offset) {
                                listp->pref_offset = offset;
                        }
                } else {
                        /*
-                        * The list could have got scheduled while this
-                        * thread was waiting for the lock
+                        * The list could have got rescheduled while
+                        * this thread was waiting for the lock
                         */
                        if (listp->scheduled) {
                                int32_t diff;
@@ -1501,9 +1720,20 @@ tcp_sched_timers(struct tcpcb *tp)
        goto done;
 
 schedule:
-       if (is_fast) {
-               listp->mode = TCP_TIMERLIST_FASTMODE;
-               listp->idlegen = 0;
+       /*
+        * Since a connection with timers is getting scheduled, the timer
+        * list moves from idle to active state and that is why idlegen is
+        * reset
+        */
+       if (mode & TCP_TIMERLIST_10MS_MODE) {
+               listp->mode = TCP_TIMERLIST_10MS_MODE;
+               listp->idleruns = 0;
+               offset = min(offset, TCP_TIMER_10MS_QUANTUM);
+       } else if (mode & TCP_TIMERLIST_100MS_MODE) {
+               if (listp->mode > TCP_TIMERLIST_100MS_MODE)
+                       listp->mode = TCP_TIMERLIST_100MS_MODE;
+               listp->idleruns = 0;
+               offset = min(offset, TCP_TIMER_100MS_QUANTUM);
        }
        tcp_sched_timerlist(offset);
 
@@ -1514,20 +1744,26 @@ done:
        return;
 }
                
-void
+static inline void
 tcp_set_lotimer_index(struct tcpcb *tp) {
-       uint16_t i, lo_index = TCPT_NONE;
+       uint16_t i, lo_index = TCPT_NONE, mode = 0;
        uint32_t lo_timer = 0;
        for (i = 0; i < TCPT_NTIMERS; ++i) {
-               if (tp->t_timer[i] != 0 &&
-                       (lo_timer == 0 || tp->t_timer[i] < lo_timer)) {
-                       lo_timer = tp->t_timer[i];
-                       lo_index = i;
+               if (tp->t_timer[i] != 0) {
+                       TCP_SET_TIMER_MODE(mode, i);
+                       if (lo_timer == 0 || tp->t_timer[i] < lo_timer) {
+                               lo_timer = tp->t_timer[i];
+                               lo_index = i;
+                       }
                }
        }
        tp->tentry.index = lo_index;
-       if (lo_index != TCPT_NONE) {
-               tp->tentry.runtime = tp->tentry.timer_start + tp->t_timer[lo_index];
+       tp->tentry.mode = mode;
+       VERIFY(tp->tentry.index == TCPT_NONE || tp->tentry.mode > 0);
+
+       if (tp->tentry.index != TCPT_NONE) {
+               tp->tentry.runtime = tp->tentry.timer_start 
+                   + tp->t_timer[tp->tentry.index];
                if (tp->tentry.runtime == 0)
                        tp->tentry.runtime++;
        }
@@ -1546,3 +1782,94 @@ tcp_check_timer_state(struct tcpcb *tp) {
        tcp_sched_timers(tp);
        return;
 }
+
+__private_extern__ void
+tcp_report_stats(void)
+{
+       struct nstat_sysinfo_data data;
+       struct sockaddr_in dst;
+       struct sockaddr_in6 dst6;
+       struct rtentry *rt = NULL;
+       u_int64_t var, uptime;  
+
+#define        stat    data.u.tcp_stats
+       if (((uptime = net_uptime()) - tcp_last_report_time) <
+               TCP_REPORT_STATS_INTERVAL)
+               return;
+
+       tcp_last_report_time = uptime;
+
+       bzero(&data, sizeof(data));
+       data.flags = NSTAT_SYSINFO_TCP_STATS;
+
+       bzero(&dst, sizeof(dst));
+       dst.sin_len = sizeof(dst);
+       dst.sin_family = AF_INET;
+
+       /* ipv4 avg rtt */
+       lck_mtx_lock(rnh_lock);
+       rt =  rt_lookup(TRUE, (struct sockaddr *)&dst, NULL,
+               rt_tables[AF_INET], IFSCOPE_NONE);
+       lck_mtx_unlock(rnh_lock);
+       if (rt != NULL) {
+               RT_LOCK(rt);
+               if (rt_primary_default(rt, rt_key(rt)) &&
+                       rt->rt_stats != NULL) {
+                       stat.ipv4_avgrtt = rt->rt_stats->nstat_avg_rtt;
+               }
+               RT_UNLOCK(rt);
+               rtfree(rt);
+               rt = NULL;
+       }
+
+       /* ipv6 avg rtt */
+       bzero(&dst6, sizeof(dst6));
+       dst6.sin6_len = sizeof(dst6);
+       dst6.sin6_family = AF_INET6;
+
+       lck_mtx_lock(rnh_lock);
+       rt = rt_lookup(TRUE,(struct sockaddr *)&dst6, NULL,
+               rt_tables[AF_INET6], IFSCOPE_NONE);
+       lck_mtx_unlock(rnh_lock);
+       if (rt != NULL) {
+               RT_LOCK(rt);
+               if (rt_primary_default(rt, rt_key(rt)) &&
+                       rt->rt_stats != NULL) {
+                       stat.ipv6_avgrtt = rt->rt_stats->nstat_avg_rtt;
+               }
+               RT_UNLOCK(rt);
+               rtfree(rt);
+               rt = NULL;
+       }
+
+       /* send packet loss rate, shift by 10 for precision */
+       if (tcpstat.tcps_sndpack > 0 && tcpstat.tcps_sndrexmitpack > 0) {
+               var = tcpstat.tcps_sndrexmitpack << 10;
+               stat.send_plr = (var * 100) / tcpstat.tcps_sndpack;
+       }
+
+       /* recv packet loss rate, shift by 10 for precision */
+       if (tcpstat.tcps_rcvpack > 0 && tcpstat.tcps_recovered_pkts > 0) {
+               var = tcpstat.tcps_recovered_pkts << 10;
+               stat.recv_plr = (var * 100) / tcpstat.tcps_rcvpack;
+       }
+
+       /* RTO after tail loss, shift by 10 for precision */
+       if (tcpstat.tcps_sndrexmitpack > 0 
+           && tcpstat.tcps_tailloss_rto > 0) {
+               var = tcpstat.tcps_tailloss_rto << 10;
+               stat.send_tlrto_rate =
+                       (var * 100) / tcpstat.tcps_sndrexmitpack;
+       }
+       
+       /* packet reordering */
+       if (tcpstat.tcps_sndpack > 0 && tcpstat.tcps_reordered_pkts > 0) {
+               var = tcpstat.tcps_reordered_pkts << 10;
+               stat.send_reorder_rate =
+                       (var * 100) / tcpstat.tcps_sndpack;
+       }
+
+       nstat_sysinfo_send_data(&data);
+
+#undef stat
+}