[CCID3]: Handle Idle and Application-Limited periods

This updates the code with regard to handling idle and application-limited
periods as specified in [RFC 4342, 5.1].

Background:

1 files changed, 40 insertions, 44 deletions

diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index 8d33a09608e9..35123c19a08f 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -133,12 +133,23 @@ static void ccid3_hc_tx_update_x(struct sock *sk, struct timeval *now)
 
 {
         struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
+        __u64 min_rate = 2 * hctx->ccid3hctx_x_recv;
         const  __u64 old_x = hctx->ccid3hctx_x;
 
+        /*
+         * Handle IDLE periods: do not reduce below RFC3390 initial sending rate
+         * when idling [RFC 4342, 5.1]. See also draft-ietf-dccp-rfc3448bis.
+         * For consistency with X and X_recv, min_rate is also scaled by 2^6.
+         */
+        if (unlikely(hctx->ccid3hctx_idle)) {
+                min_rate = rfc3390_initial_rate(sk);
+                min_rate = max(min_rate, 2 * hctx->ccid3hctx_x_recv);
+        }
+
         if (hctx->ccid3hctx_p > 0) {
 
                 hctx->ccid3hctx_x = min(((__u64)hctx->ccid3hctx_x_calc) << 6,
-                                        hctx->ccid3hctx_x_recv * 2);
+                                        min_rate);
                 hctx->ccid3hctx_x = max(hctx->ccid3hctx_x,
                                         (((__u64)hctx->ccid3hctx_s) << 6) /
                                                                 TFRC_T_MBI);
@@ -147,7 +158,7 @@ static void ccid3_hc_tx_update_x(struct sock *sk, struct timeval *now)
                         (suseconds_t)hctx->ccid3hctx_rtt >= 0) {
 
                 hctx->ccid3hctx_x =
-                        max(2 * min(hctx->ccid3hctx_x, hctx->ccid3hctx_x_recv),
+                        max(min(2 * hctx->ccid3hctx_x, min_rate),
                             scaled_div(((__u64)hctx->ccid3hctx_s) << 6,
                                        hctx->ccid3hctx_rtt));
                 hctx->ccid3hctx_t_ld = *now;
@@ -209,6 +220,7 @@ static void ccid3_hc_tx_no_feedback_timer(unsigned long data)
 {
         struct sock *sk = (struct sock *)data;
         struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
+        struct timeval now;
         unsigned long t_nfb = USEC_PER_SEC / 5;
 
         bh_lock_sock(sk);
@@ -221,6 +233,8 @@ static void ccid3_hc_tx_no_feedback_timer(unsigned long data)
         ccid3_pr_debug("%s(%p, state=%s) - entry \n", dccp_role(sk), sk,
                        ccid3_tx_state_name(hctx->ccid3hctx_state));
 
+        hctx->ccid3hctx_idle = 1;
+
         switch (hctx->ccid3hctx_state) {
         case TFRC_SSTATE_NO_FBACK:
                 /* RFC 3448, 4.4: Halve send rate directly */
@@ -239,49 +253,33 @@ static void ccid3_hc_tx_no_feedback_timer(unsigned long data)
                 break;
         case TFRC_SSTATE_FBACK:
                 /*
-                 * Check if IDLE since last timeout and recv rate is less than
-                 * 4 packets (in units of 64*bytes/sec) per RTT
+                 *  Modify the cached value of X_recv [RFC 3448, 4.4]
+                 *
+                 *  If (p == 0 || X_calc > 2 * X_recv)
+                 *    X_recv = max(X_recv / 2, s / (2 * t_mbi));
+                 *  Else
+                 *    X_recv = X_calc / 4;
+                 *
+                 *  Note that X_recv is scaled by 2^6 while X_calc is not
                  */
-                if (!hctx->ccid3hctx_idle ||
-                    (hctx->ccid3hctx_x_recv >= 4 *
-                     scaled_div(((__u64)hctx->ccid3hctx_s) << 6,
-                                hctx->ccid3hctx_rtt))) {
-                        struct timeval now;
+                BUG_ON(hctx->ccid3hctx_p && !hctx->ccid3hctx_x_calc);
 
-                        ccid3_pr_debug("%s(%p, state=%s), not idle\n",
-                                       dccp_role(sk), sk,
-                                   ccid3_tx_state_name(hctx->ccid3hctx_state));
+                if (hctx->ccid3hctx_p == 0 ||
+                    (hctx->ccid3hctx_x_calc > (hctx->ccid3hctx_x_recv >> 5))) {
 
-                        /*
-                         *  Modify the cached value of X_recv [RFC 3448, 4.4]
-                         *
-                         *  If (p == 0 || X_calc > 2 * X_recv)
-                         *    X_recv = max(X_recv / 2, s / (2 * t_mbi));
-                         *  Else
-                         *    X_recv = X_calc / 4;
-                         *
-                         *  Note that X_recv is scaled by 2^6 while X_calc is not
-                         */
-                        BUG_ON(hctx->ccid3hctx_p && !hctx->ccid3hctx_x_calc);
-
-                        if (hctx->ccid3hctx_p  == 0 ||
-                            (hctx->ccid3hctx_x_calc >
-                             (hctx->ccid3hctx_x_recv >> 5))) {
-
-                                hctx->ccid3hctx_x_recv =
-                                        max(hctx->ccid3hctx_x_recv / 2,
-                                            (((__u64)hctx->ccid3hctx_s) << 6) /
-                                                          (2 * TFRC_T_MBI));
-
-                                if (hctx->ccid3hctx_p == 0)
-                                        dccp_timestamp(sk, &now);
-                        } else {
-                                hctx->ccid3hctx_x_recv = hctx->ccid3hctx_x_calc;
-                                hctx->ccid3hctx_x_recv <<= 4;
-                        }
-                        /* Now recalculate X [RFC 3448, 4.3, step (4)] */
-                        ccid3_hc_tx_update_x(sk, &now);
+                        hctx->ccid3hctx_x_recv =
+                                max(hctx->ccid3hctx_x_recv / 2,
+                                    (((__u64)hctx->ccid3hctx_s) << 6) /
+                                                              (2 * TFRC_T_MBI));
+
+                        if (hctx->ccid3hctx_p == 0)
+                                dccp_timestamp(sk, &now);
+                } else {
+                        hctx->ccid3hctx_x_recv = hctx->ccid3hctx_x_calc;
+                        hctx->ccid3hctx_x_recv <<= 4;
                 }
+                /* Now recalculate X [RFC 3448, 4.3, step (4)] */
+                ccid3_hc_tx_update_x(sk, &now);
                 /*
                  * Schedule no feedback timer to expire in
                  * max(t_RTO, 2 * s/X)  =  max(t_RTO, 2 * t_ipi)
@@ -296,8 +294,6 @@ static void ccid3_hc_tx_no_feedback_timer(unsigned long data)
                 goto out;
         }
 
-        hctx->ccid3hctx_idle = 1;
-
 restart_timer:
         sk_reset_timer(sk, &hctx->ccid3hctx_no_feedback_timer,
                            jiffies + usecs_to_jiffies(t_nfb));
@@ -377,6 +373,7 @@ static int ccid3_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
         /* prepare to send now (add options etc.) */
         dp->dccps_hc_tx_insert_options = 1;
         DCCP_SKB_CB(skb)->dccpd_ccval = hctx->ccid3hctx_last_win_count;
+        hctx->ccid3hctx_idle = 0;
 
         /* set the nominal send time for the next following packet */
         timeval_add_usecs(&hctx->ccid3hctx_t_nom, hctx->ccid3hctx_t_ipi);
@@ -407,7 +404,6 @@ static void ccid3_hc_tx_packet_sent(struct sock *sk, int more,
         packet->dccphtx_seqno  = dccp_sk(sk)->dccps_gss;
         packet->dccphtx_rtt    = hctx->ccid3hctx_rtt;
         packet->dccphtx_sent   = 1;
-        hctx->ccid3hctx_idle   = 0;
 }
 
 static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)