xnu-7195.81.3.tar.gz

[apple/xnu.git] / bsd / netinet / tcp_ledbat.c

diff --git a/bsd/netinet/tcp_ledbat.c b/bsd/netinet/tcp_ledbat.c
index 9e18bf9ebc9ca589b72553a063718c6f40a65bd1..f345934a720e31a7bf754729cb83630c07e65fa5 100644 (file)
--- a/bsd/netinet/tcp_ledbat.c
+++ b/bsd/netinet/tcp_ledbat.c
@@ -1,5 +1,5 @@
 /*
 /*

- * Copyright (c) 2010-2014 Apple Inc. All rights reserved.
+ * Copyright (c) 2010-2020 Apple Inc. All rights reserved.

  *
  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
  *
  *
  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
  *


@@ -37,9 +37,7 @@
 #include <netinet/in_systm.h>
 #include <netinet/ip.h>
 
 #include <netinet/in_systm.h>
 #include <netinet/ip.h>
 

-#if INET6

 #include <netinet/ip6.h>
 #include <netinet/ip6.h>

-#endif

 #include <netinet/ip_var.h>
 #include <netinet/tcp.h>
 #include <netinet/tcp_fsm.h>
 #include <netinet/ip_var.h>
 #include <netinet/tcp.h>
 #include <netinet/tcp_fsm.h>


@@ -64,7 +62,7 @@ void tcp_ledbat_pre_fr(struct tcpcb *tp);
 void tcp_ledbat_post_fr(struct tcpcb *tp, struct tcphdr *th);
 void tcp_ledbat_after_idle(struct tcpcb *tp);
 void tcp_ledbat_after_timeout(struct tcpcb *tp);
 void tcp_ledbat_post_fr(struct tcpcb *tp, struct tcphdr *th);
 void tcp_ledbat_after_idle(struct tcpcb *tp);
 void tcp_ledbat_after_timeout(struct tcpcb *tp);

-int tcp_ledbat_delay_ack(struct tcpcb *tp, struct tcphdr *th);
+static int tcp_ledbat_delay_ack(struct tcpcb *tp, struct tcphdr *th);

 void tcp_ledbat_switch_cc(struct tcpcb *tp, uint16_t old_cc_index);
 
 struct tcp_cc_algo tcp_cc_ledbat = {
 void tcp_ledbat_switch_cc(struct tcpcb *tp, uint16_t old_cc_index);
 
 struct tcp_cc_algo tcp_cc_ledbat = {


@@ -82,64 +80,63 @@ struct tcp_cc_algo tcp_cc_ledbat = {
        .switch_to = tcp_ledbat_switch_cc
 };
 
        .switch_to = tcp_ledbat_switch_cc
 };
 

-/* Target queuing delay in milliseconds. This includes the processing 
- * and scheduling delay on both of the end-hosts. A LEDBAT sender tries 
+/* Target queuing delay in milliseconds. This includes the processing
+ * and scheduling delay on both of the end-hosts. A LEDBAT sender tries

  * to keep queuing delay below this limit. When the queuing delay
  * to keep queuing delay below this limit. When the queuing delay

- * goes above this limit, a LEDBAT sender will start reducing the 
+ * goes above this limit, a LEDBAT sender will start reducing the

  * congestion window.
  *
  * congestion window.
  *

- * The LEDBAT draft says that target queue delay MUST be 100 ms for 
+ * The LEDBAT draft says that target queue delay MUST be 100 ms for

  * inter-operability.
  */
  * inter-operability.
  */

-int target_qdelay = 100;
-SYSCTL_INT(_net_inet_tcp, OID_AUTO, bg_target_qdelay, CTLFLAG_RW | CTLFLAG_LOCKED, 
-       &target_qdelay , 100, "Target queuing delay");
+SYSCTL_SKMEM_TCP_INT(OID_AUTO, bg_target_qdelay, CTLFLAG_RW | CTLFLAG_LOCKED,
+    int, target_qdelay, 100, "Target queuing delay");

 
 /* Allowed increase and tether are used to place an upper bound on
  * congestion window based on the amount of data that is outstanding.
 
 /* Allowed increase and tether are used to place an upper bound on
  * congestion window based on the amount of data that is outstanding.

- * This will limit the congestion window when the amount of data in 
+ * This will limit the congestion window when the amount of data in

  * flight is little because the application is writing to the socket
  * flight is little because the application is writing to the socket

- * intermittently and is preventing the connection from becoming idle . 
+ * intermittently and is preventing the connection from becoming idle .

  *
  * max_allowed_cwnd = allowed_increase + (tether * flight_size)
  * cwnd = min(cwnd, max_allowed_cwnd)
  *
  * 'Allowed_increase' parameter is set to 8. If the flight size is zero, then
  * we want the congestion window to be at least 8 packets to reduce the
  *
  * max_allowed_cwnd = allowed_increase + (tether * flight_size)
  * cwnd = min(cwnd, max_allowed_cwnd)
  *
  * 'Allowed_increase' parameter is set to 8. If the flight size is zero, then
  * we want the congestion window to be at least 8 packets to reduce the

- * delay induced by delayed ack. This helps when the receiver is acking 
+ * delay induced by delayed ack. This helps when the receiver is acking

  * more than 2 packets at a time (stretching acks for better performance).
  * more than 2 packets at a time (stretching acks for better performance).

- * 
+ *

  * 'Tether' is also set to 2. We do not want this to limit the growth of cwnd
  * during slow-start.
  * 'Tether' is also set to 2. We do not want this to limit the growth of cwnd
  * during slow-start.

- */ 
-int allowed_increase = 8;
-SYSCTL_INT(_net_inet_tcp, OID_AUTO, bg_allowed_increase, CTLFLAG_RW | CTLFLAG_LOCKED, 
-       &allowed_increase, 1, "Additive constant used to calculate max allowed congestion window");
+ */
+SYSCTL_SKMEM_TCP_INT(OID_AUTO, bg_allowed_increase, CTLFLAG_RW | CTLFLAG_LOCKED,
+    int, allowed_increase, 8,
+    "Additive constant used to calculate max allowed congestion window");

 
 /* Left shift for cwnd to get tether value of 2 */
 
 /* Left shift for cwnd to get tether value of 2 */

-int tether_shift = 1;
-SYSCTL_INT(_net_inet_tcp, OID_AUTO, bg_tether_shift, CTLFLAG_RW | CTLFLAG_LOCKED, 
-       &tether_shift, 1, "Tether shift for max allowed congestion window");
+SYSCTL_SKMEM_TCP_INT(OID_AUTO, bg_tether_shift, CTLFLAG_RW | CTLFLAG_LOCKED,
+    int, tether_shift, 1, "Tether shift for max allowed congestion window");

 
 

-/* Start with an initial window of 2. This will help to get more accurate 
+/* Start with an initial window of 2. This will help to get more accurate

  * minimum RTT measurement in the beginning. It will help to probe
  * the path slowly and will not add to the existing delay if the path is
  * already congested. Using 2 packets will reduce the delay induced by delayed-ack.
  */
  * minimum RTT measurement in the beginning. It will help to probe
  * the path slowly and will not add to the existing delay if the path is
  * already congested. Using 2 packets will reduce the delay induced by delayed-ack.
  */

-uint32_t bg_ss_fltsz = 2;
-SYSCTL_INT(_net_inet_tcp, OID_AUTO, bg_ss_fltsz, CTLFLAG_RW | CTLFLAG_LOCKED,
-       &bg_ss_fltsz, 2, "Initial congestion window for background transport");
+SYSCTL_SKMEM_TCP_INT(OID_AUTO, bg_ss_fltsz, CTLFLAG_RW | CTLFLAG_LOCKED,
+    uint32_t, bg_ss_fltsz, 2, "Initial congestion window for background transport");

 
 extern int rtt_samples_per_slot;
 
 
 extern int rtt_samples_per_slot;
 

-static void update_cwnd(struct tcpcb *tp, uint32_t incr) {
+static void
+update_cwnd(struct tcpcb *tp, uint32_t incr)
+{

        uint32_t max_allowed_cwnd = 0, flight_size = 0;
        uint32_t base_rtt;
 
        base_rtt = get_base_rtt(tp);
 
        /* If we do not have a good RTT measurement yet, increment
        uint32_t max_allowed_cwnd = 0, flight_size = 0;
        uint32_t base_rtt;
 
        base_rtt = get_base_rtt(tp);
 
        /* If we do not have a good RTT measurement yet, increment

-        * congestion window by the default value.  
+        * congestion window by the default value.

         */
        if (base_rtt == 0 || tp->t_rttcur == 0) {
                tp->snd_cwnd += incr;
         */
        if (base_rtt == 0 || tp->t_rttcur == 0) {
                tp->snd_cwnd += incr;


@@ -153,30 +150,32 @@ static void update_cwnd(struct tcpcb *tp, uint32_t incr) {
                 *
                 * Move background slow-start threshold to current
                 * congestion window so that the next time (after some idle
                 *
                 * Move background slow-start threshold to current
                 * congestion window so that the next time (after some idle

-                * period), we can attempt to do slow-start till here if there 
+                * period), we can attempt to do slow-start till here if there

                 * is no increase in rtt
                 */
                 * is no increase in rtt
                 */

-               if (tp->bg_ssthresh < tp->snd_cwnd)
+               if (tp->bg_ssthresh < tp->snd_cwnd) {

                        tp->bg_ssthresh = tp->snd_cwnd;
                        tp->bg_ssthresh = tp->snd_cwnd;

-               tp->snd_cwnd += incr;   
-
+               }
+               tp->snd_cwnd += incr;

        } else {
        } else {

-               /* In response to an increase in rtt, reduce the congestion 
-                * window by one-eighth. This will help to yield immediately 
+               /* In response to an increase in rtt, reduce the congestion
+                * window by one-eighth. This will help to yield immediately

                 * to a competing stream.
                 */
                uint32_t redwin;
 
                 * to a competing stream.
                 */
                uint32_t redwin;
 

-               redwin = tp->snd_cwnd >> 3;  
+               redwin = tp->snd_cwnd >> 3;

                tp->snd_cwnd -= redwin;
                tp->snd_cwnd -= redwin;

-               if (tp->snd_cwnd < bg_ss_fltsz * tp->t_maxseg)
+               if (tp->snd_cwnd < bg_ss_fltsz * tp->t_maxseg) {

                        tp->snd_cwnd = bg_ss_fltsz * tp->t_maxseg;
                        tp->snd_cwnd = bg_ss_fltsz * tp->t_maxseg;

+               }

 
 

-               /* Lower background slow-start threshold so that the connection 
+               /* Lower background slow-start threshold so that the connection

                 * will go into congestion avoidance phase
                 */
                 * will go into congestion avoidance phase
                 */

-               if (tp->bg_ssthresh > tp->snd_cwnd)
+               if (tp->bg_ssthresh > tp->snd_cwnd) {

                        tp->bg_ssthresh = tp->snd_cwnd;
                        tp->bg_ssthresh = tp->snd_cwnd;

+               }

        }
 check_max:
        /* Calculate the outstanding flight size and restrict the
        }
 check_max:
        /* Calculate the outstanding flight size and restrict the


@@ -184,40 +183,46 @@ check_max:
         */
        flight_size = tp->snd_max - tp->snd_una;
 
         */
        flight_size = tp->snd_max - tp->snd_una;
 

-       max_allowed_cwnd = (allowed_increase * tp->t_maxseg) 
-               + (flight_size << tether_shift);
+       max_allowed_cwnd = (allowed_increase * tp->t_maxseg)
+           + (flight_size << tether_shift);

        tp->snd_cwnd = min(tp->snd_cwnd, max_allowed_cwnd);
        return;
 }
 
        tp->snd_cwnd = min(tp->snd_cwnd, max_allowed_cwnd);
        return;
 }
 

-int tcp_ledbat_init(struct tcpcb *tp) {
+int
+tcp_ledbat_init(struct tcpcb *tp)
+{

 #pragma unused(tp)
        OSIncrementAtomic((volatile SInt32 *)&tcp_cc_ledbat.num_sockets);
        return 0;
 }
 
 #pragma unused(tp)
        OSIncrementAtomic((volatile SInt32 *)&tcp_cc_ledbat.num_sockets);
        return 0;
 }
 

-int tcp_ledbat_cleanup(struct tcpcb *tp) {
+int
+tcp_ledbat_cleanup(struct tcpcb *tp)
+{

 #pragma unused(tp)
        OSDecrementAtomic((volatile SInt32 *)&tcp_cc_ledbat.num_sockets);
        return 0;
 }
 
 #pragma unused(tp)
        OSDecrementAtomic((volatile SInt32 *)&tcp_cc_ledbat.num_sockets);
        return 0;
 }
 

-/* Initialize the congestion window for a connection 
- * 
+/* Initialize the congestion window for a connection
+ *

  */
 
 void
  */
 
 void

-tcp_ledbat_cwnd_init(struct tcpcb *tp) {
+tcp_ledbat_cwnd_init(struct tcpcb *tp)
+{

        tp->snd_cwnd = tp->t_maxseg * bg_ss_fltsz;
        tp->bg_ssthresh = tp->snd_ssthresh;
 }
 
        tp->snd_cwnd = tp->t_maxseg * bg_ss_fltsz;
        tp->bg_ssthresh = tp->snd_ssthresh;
 }
 

-/* Function to handle an in-sequence ack which is fast-path processing 
- * of an in sequence ack in tcp_input function (called as header prediction). 
+/* Function to handle an in-sequence ack which is fast-path processing
+ * of an in sequence ack in tcp_input function (called as header prediction).

  * This gets called only during congestion avoidance phase.
  */
 void
  * This gets called only during congestion avoidance phase.
  */
 void

-tcp_ledbat_congestion_avd(struct tcpcb *tp, struct tcphdr *th) {
+tcp_ledbat_congestion_avd(struct tcpcb *tp, struct tcphdr *th)
+{

        int acked = 0;
        u_int32_t incr = 0;
 
        int acked = 0;
        u_int32_t incr = 0;
 


@@ -235,7 +240,8 @@ tcp_ledbat_congestion_avd(struct tcpcb *tp, struct tcphdr *th) {
 /* Function to process an ack.
  */
 void
 /* Function to process an ack.
  */
 void

-tcp_ledbat_ack_rcvd(struct tcpcb *tp, struct tcphdr *th) {
+tcp_ledbat_ack_rcvd(struct tcpcb *tp, struct tcphdr *th)
+{

        /*
         * RFC 3465 - Appropriate Byte Counting.
         *
        /*
         * RFC 3465 - Appropriate Byte Counting.
         *


@@ -249,9 +255,9 @@ tcp_ledbat_ack_rcvd(struct tcpcb *tp, struct tcphdr *th) {
         * greater than or equal to the congestion window.
         */
 
         * greater than or equal to the congestion window.
         */
 

-       register u_int cw = tp->snd_cwnd;
-       register u_int incr = tp->t_maxseg;
-       int acked = 0;
+       uint32_t cw = tp->snd_cwnd;
+       uint32_t incr = tp->t_maxseg;
+       uint32_t acked = 0;

 
        acked = BYTES_ACKED(th, tp);
        tp->t_bytes_acked += acked;
 
        acked = BYTES_ACKED(th, tp);
        tp->t_bytes_acked += acked;


@@ -271,37 +277,46 @@ tcp_ledbat_ack_rcvd(struct tcpcb *tp, struct tcphdr *th) {
                 */
                u_int abc_lim;
 
                 */
                u_int abc_lim;
 

-               abc_lim = (tcp_do_rfc3465_lim2 &&
-                       tp->snd_nxt == tp->snd_max) ? incr * 2 : incr;
+               abc_lim = (tp->snd_nxt == tp->snd_max) ? incr * 2 : incr;

 
 

-               incr = lmin(acked, abc_lim);
+               incr = ulmin(acked, abc_lim);

        }
        }

-       if (tp->t_bytes_acked >= cw)
+       if (tp->t_bytes_acked >= cw) {

                tp->t_bytes_acked -= cw;
                tp->t_bytes_acked -= cw;

-       if (incr > 0) 
+       }
+       if (incr > 0) {

                update_cwnd(tp, incr);
                update_cwnd(tp, incr);

+       }

 }
 
 void
 }
 
 void

-tcp_ledbat_pre_fr(struct tcpcb *tp) {
+tcp_ledbat_pre_fr(struct tcpcb *tp)
+{

        uint32_t win;
 
        uint32_t win;
 

-       win = min(tp->snd_wnd, tp->snd_cwnd) / 
-               2 / tp->t_maxseg;
-       if ( win < 2 )
+       win = min(tp->snd_wnd, tp->snd_cwnd) /
+           2 / tp->t_maxseg;
+       if (win < 2) {

                win = 2;
                win = 2;

-       tp->snd_ssthresh = win * tp->t_maxseg; 
-       if (tp->bg_ssthresh > tp->snd_ssthresh)
+       }
+       tp->snd_ssthresh = win * tp->t_maxseg;
+       if (tp->bg_ssthresh > tp->snd_ssthresh) {

                tp->bg_ssthresh = tp->snd_ssthresh;
                tp->bg_ssthresh = tp->snd_ssthresh;

+       }

 
        tcp_cc_resize_sndbuf(tp);
 }
 
 void
 
        tcp_cc_resize_sndbuf(tp);
 }
 
 void

-tcp_ledbat_post_fr(struct tcpcb *tp, struct tcphdr *th) {
+tcp_ledbat_post_fr(struct tcpcb *tp, struct tcphdr *th)
+{

        int32_t ss;
 
        int32_t ss;
 

-       ss = tp->snd_max - th->th_ack;
+       if (th) {
+               ss = tp->snd_max - th->th_ack;
+       } else {
+               ss = tp->snd_max - tp->snd_una;
+       }

 
        /*
         * Complete ack.  Inflate the congestion window to
 
        /*
         * Complete ack.  Inflate the congestion window to


@@ -312,14 +327,15 @@ tcp_ledbat_post_fr(struct tcpcb *tp, struct tcphdr *th) {
         * would be inclined to send a burst, better to do
         * it via the slow start mechanism.
         *
         * would be inclined to send a burst, better to do
         * it via the slow start mechanism.
         *

-        * If the flight size is zero, then make congestion 
-        * window to be worth at least 2 segments to avoid 
+        * If the flight size is zero, then make congestion
+        * window to be worth at least 2 segments to avoid

         * delayed acknowledgement (draft-ietf-tcpm-rfc3782-bis-05).
         */
         * delayed acknowledgement (draft-ietf-tcpm-rfc3782-bis-05).
         */

-       if (ss < (int32_t)tp->snd_ssthresh)
+       if (ss < (int32_t)tp->snd_ssthresh) {

                tp->snd_cwnd = max(ss, tp->t_maxseg) + tp->t_maxseg;
                tp->snd_cwnd = max(ss, tp->t_maxseg) + tp->t_maxseg;

-       else
+       } else {

                tp->snd_cwnd = tp->snd_ssthresh;
                tp->snd_cwnd = tp->snd_ssthresh;

+       }

        tp->t_bytes_acked = 0;
 }
 
        tp->t_bytes_acked = 0;
 }
 


@@ -329,13 +345,13 @@ tcp_ledbat_post_fr(struct tcpcb *tp, struct tcphdr *th) {
  * Clear base history after idle time.
  */
 void
  * Clear base history after idle time.
  */
 void

-tcp_ledbat_after_idle(struct tcpcb *tp) {
-       
+tcp_ledbat_after_idle(struct tcpcb *tp)
+{

        /* Reset the congestion window */
        tp->snd_cwnd = tp->t_maxseg * bg_ss_fltsz;
 }
 
        /* Reset the congestion window */
        tp->snd_cwnd = tp->t_maxseg * bg_ss_fltsz;
 }
 

-/* Function to change the congestion window when the retransmit 
+/* Function to change the congestion window when the retransmit

  * timer fires. The behavior is the same as that for best-effort
  * TCP, reduce congestion window to one segment and start probing
  * the link using "slow start". The slow start threshold is set
  * timer fires. The behavior is the same as that for best-effort
  * TCP, reduce congestion window to one segment and start probing
  * the link using "slow start". The slow start threshold is set


@@ -343,15 +359,18 @@ tcp_ledbat_after_idle(struct tcpcb *tp) {
  * threshold also.
  */
 void
  * threshold also.
  */
 void

-tcp_ledbat_after_timeout(struct tcpcb *tp) {
-       if (tp->t_state >=  TCPS_ESTABLISHED) {
+tcp_ledbat_after_timeout(struct tcpcb *tp)
+{
+       if (tp->t_state >= TCPS_ESTABLISHED) {

                u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
                u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;

-               if (win < 2)
+               if (win < 2) {

                        win = 2;
                        win = 2;

+               }

                tp->snd_ssthresh = win * tp->t_maxseg;
 
                tp->snd_ssthresh = win * tp->t_maxseg;
 

-               if (tp->bg_ssthresh > tp->snd_ssthresh)
+               if (tp->bg_ssthresh > tp->snd_ssthresh) {

                        tp->bg_ssthresh = tp->snd_ssthresh;
                        tp->bg_ssthresh = tp->snd_ssthresh;

+               }

 
                tp->snd_cwnd = tp->t_maxseg;
                tcp_cc_resize_sndbuf(tp);
 
                tp->snd_cwnd = tp->t_maxseg;
                tcp_cc_resize_sndbuf(tp);


@@ -362,51 +381,54 @@ tcp_ledbat_after_timeout(struct tcpcb *tp) {
  * Indicate whether this ack should be delayed.
  * We can delay the ack if:
  *      - our last ack wasn't a 0-sized window.
  * Indicate whether this ack should be delayed.
  * We can delay the ack if:
  *      - our last ack wasn't a 0-sized window.

- *      - the peer hasn't sent us a TH_PUSH data packet: if he did, take this 
- *     as a clue that we need to ACK without any delay. This helps higher 
- *     level protocols who won't send us more data even if the window is 
- *     open because their last "segment" hasn't been ACKed
+ *      - the peer hasn't sent us a TH_PUSH data packet: if he did, take this
+ *      as a clue that we need to ACK without any delay. This helps higher
+ *     level protocols who won't send us more data even if the window is
+ *      open because their last "segment" hasn't been ACKed

  * Otherwise the receiver will ack every other full-sized segment or when the
  * Otherwise the receiver will ack every other full-sized segment or when the

- * delayed ack timer fires. This will help to generate better rtt estimates for 
+ * delayed ack timer fires. This will help to generate better rtt estimates for

  * the other end if it is a ledbat sender.
  * the other end if it is a ledbat sender.

- * 
+ *

  */
 
  */
 

-int
-tcp_ledbat_delay_ack(struct tcpcb *tp, struct tcphdr *th) {
-       /* If any flag other than TH_ACK is set, set "end-of-write" bit */
-       if (th->th_flags & ~TH_ACK)
-               tp->t_flagsext |= TF_STREAMEOW;
-       else
-               tp->t_flagsext &= ~(TF_STREAMEOW);
-
-       if ((tp->t_flags & TF_RXWIN0SENT) == 0 &&
-               (th->th_flags & TH_PUSH) == 0 &&
-               (tp->t_unacksegs == 1))
-               return(1);
-       return(0);
+static int
+tcp_ledbat_delay_ack(struct tcpcb *tp, struct tcphdr *th)
+{
+       if (tcp_ack_strategy == TCP_ACK_STRATEGY_MODERN) {
+               return tcp_cc_delay_ack(tp, th);
+       } else {
+               if ((tp->t_flags & TF_RXWIN0SENT) == 0 &&
+                   (th->th_flags & TH_PUSH) == 0 && (tp->t_unacksegs == 1)) {
+                       return 1;
+               }
+               return 0;
+       }

 }
 
 /* Change a connection to use ledbat. First, lower bg_ssthresh value
 }
 
 /* Change a connection to use ledbat. First, lower bg_ssthresh value

- * if it needs to be. 
+ * if it needs to be.

  */
 void
  */
 void

-tcp_ledbat_switch_cc(struct tcpcb *tp, uint16_t old_cc_index) {
+tcp_ledbat_switch_cc(struct tcpcb *tp, uint16_t old_cc_index)
+{

 #pragma unused(old_cc_index)
        uint32_t cwnd;
 
 #pragma unused(old_cc_index)
        uint32_t cwnd;
 

-       if (tp->bg_ssthresh == 0 || tp->bg_ssthresh > tp->snd_ssthresh)
+       if (tp->bg_ssthresh == 0 || tp->bg_ssthresh > tp->snd_ssthresh) {

                tp->bg_ssthresh = tp->snd_ssthresh;
                tp->bg_ssthresh = tp->snd_ssthresh;

+       }

 
        cwnd = min(tp->snd_wnd, tp->snd_cwnd);
 
 
        cwnd = min(tp->snd_wnd, tp->snd_cwnd);
 

-       if (tp->snd_cwnd > tp->bg_ssthresh)
+       if (tp->snd_cwnd > tp->bg_ssthresh) {

                cwnd = cwnd / tp->t_maxseg;
                cwnd = cwnd / tp->t_maxseg;

-       else
+       } else {

                cwnd = cwnd / 2 / tp->t_maxseg;
                cwnd = cwnd / 2 / tp->t_maxseg;

+       }

 
 

-       if (cwnd < bg_ss_fltsz)
+       if (cwnd < bg_ss_fltsz) {

                cwnd = bg_ss_fltsz;
                cwnd = bg_ss_fltsz;

+       }

 
        tp->snd_cwnd = cwnd * tp->t_maxseg;
        tp->t_bytes_acked = 0;
 
        tp->snd_cwnd = cwnd * tp->t_maxseg;
        tp->t_bytes_acked = 0;