[DCCP] CCID2: Halve cwnd once upon multiple losses in a single RTT

When multiple losses occur in one RTT, the window should be halved
only once [a single "congestion event"].  This is now implemented,
although not perfectly.  Slightly changed the interface for changing
the cwnd: pass hctx instead of dp.  This is required in order to allow
for change_cwnd to be called from _init().

Signed-off-by: Andrea Bittau <a.bittau@cs.ucl.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c
index 93a30ae8d07a67747b2e552a3b5385e02b159ca1..b88da035865f3e9e7aca9e4adef866d5d6cc32af 100644 (file)
--- a/net/dccp/ccids/ccid2.c
+++ b/net/dccp/ccids/ccid2.c
@@ -187,10 +187,8 @@ static void ccid2_change_l_ack_ratio(struct sock *sk, int val)
        dp->dccps_l_ack_ratio = val;
 }
 
-static void ccid2_change_cwnd(struct sock *sk, int val)
+static void ccid2_change_cwnd(struct ccid2_hc_tx_sock *hctx, int val)
 {
-       struct ccid2_hc_tx_sock *hctx = ccid2_hc_tx_sk(sk);
-
        if (val == 0)
                val = 1;
 
@@ -234,7 +232,7 @@ static void ccid2_hc_tx_rto_expire(unsigned long data)
        hctx->ccid2hctx_ssthresh = hctx->ccid2hctx_cwnd >> 1;
        if (hctx->ccid2hctx_ssthresh < 2)
                hctx->ccid2hctx_ssthresh = 2;
-       ccid2_change_cwnd(sk, 1);
+       ccid2_change_cwnd(hctx, 1);
 
        /* clear state about stuff we sent */
        hctx->ccid2hctx_seqt    = hctx->ccid2hctx_seqh;
@@ -444,7 +442,7 @@ static inline void ccid2_new_ack(struct sock *sk,
                        /* increase every 2 acks */
                        hctx->ccid2hctx_ssacks++;
                        if (hctx->ccid2hctx_ssacks == 2) {
-                               ccid2_change_cwnd(sk, hctx->ccid2hctx_cwnd + 1);
+                               ccid2_change_cwnd(hctx, hctx->ccid2hctx_cwnd+1);
                                hctx->ccid2hctx_ssacks = 0;
                                *maxincr = *maxincr - 1;
                        }
@@ -457,7 +455,7 @@ static inline void ccid2_new_ack(struct sock *sk,
                hctx->ccid2hctx_acks++;
 
                if (hctx->ccid2hctx_acks >= hctx->ccid2hctx_cwnd) {
-                       ccid2_change_cwnd(sk, hctx->ccid2hctx_cwnd + 1);
+                       ccid2_change_cwnd(hctx, hctx->ccid2hctx_cwnd + 1);
                        hctx->ccid2hctx_acks = 0;
                }
        }
@@ -532,6 +530,22 @@ static void ccid2_hc_tx_dec_pipe(struct sock *sk)
                ccid2_hc_tx_kill_rto_timer(sk);
 }
 
+static void ccid2_congestion_event(struct ccid2_hc_tx_sock *hctx,
+                                  struct ccid2_seq *seqp)
+{
+       if (time_before(seqp->ccid2s_sent, hctx->ccid2hctx_last_cong)) {
+               ccid2_pr_debug("Multiple losses in an RTT---treating as one\n");
+               return;
+       }
+
+       hctx->ccid2hctx_last_cong = jiffies;
+
+       ccid2_change_cwnd(hctx, hctx->ccid2hctx_cwnd >> 1);
+       hctx->ccid2hctx_ssthresh = hctx->ccid2hctx_cwnd;
+       if (hctx->ccid2hctx_ssthresh < 2)
+               hctx->ccid2hctx_ssthresh = 2;
+}
+
 static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
 {
        struct dccp_sock *dp = dccp_sk(sk);
@@ -542,7 +556,6 @@ static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
        unsigned char veclen;
        int offset = 0;
        int done = 0;
-       int loss = 0;
        unsigned int maxincr = 0;
 
        ccid2_hc_tx_check_sanity(hctx);
@@ -636,7 +649,8 @@ static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
                                    !seqp->ccid2s_acked) {
                                        if (state ==
                                            DCCP_ACKVEC_STATE_ECN_MARKED) {
-                                               loss = 1;
+                                               ccid2_congestion_event(hctx,
+                                                                      seqp);
                                        } else
                                                ccid2_new_ack(sk, seqp,
                                                              &maxincr);
@@ -688,7 +702,13 @@ static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
                /* check for lost packets */
                while (1) {
                        if (!seqp->ccid2s_acked) {
-                               loss = 1;
+                               ccid2_pr_debug("Packet lost: %llu\n",
+                                              seqp->ccid2s_seq);
+                               /* XXX need to traverse from tail -> head in
+                                * order to detect multiple congestion events in
+                                * one ack vector.
+                                */
+                               ccid2_congestion_event(hctx, seqp);
                                ccid2_hc_tx_dec_pipe(sk);
                        }
                        if (seqp == hctx->ccid2hctx_seqt)
@@ -707,14 +727,6 @@ static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
                hctx->ccid2hctx_seqt = hctx->ccid2hctx_seqt->ccid2s_next;
        }
 
-       if (loss) {
-               /* XXX do bit shifts guarantee a 0 as the new bit? */
-               ccid2_change_cwnd(sk, hctx->ccid2hctx_cwnd >> 1);
-               hctx->ccid2hctx_ssthresh = hctx->ccid2hctx_cwnd;
-               if (hctx->ccid2hctx_ssthresh < 2)
-                       hctx->ccid2hctx_ssthresh = 2;
-       }
-
        ccid2_hc_tx_check_sanity(hctx);
 }
 
@@ -722,7 +734,7 @@ static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk)
 {
         struct ccid2_hc_tx_sock *hctx = ccid_priv(ccid);
 
-       hctx->ccid2hctx_cwnd      = 1;
+       ccid2_change_cwnd(hctx, 1);
        /* Initialize ssthresh to infinity.  This means that we will exit the
         * initial slow-start after the first packet loss.  This is what we
         * want.
@@ -741,6 +753,7 @@ static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk)
        hctx->ccid2hctx_rttvar   = -1;
        hctx->ccid2hctx_lastrtt  = 0;
        hctx->ccid2hctx_rpdupack = -1;
+       hctx->ccid2hctx_last_cong = jiffies;
 
        hctx->ccid2hctx_rtotimer.function = &ccid2_hc_tx_rto_expire;
        hctx->ccid2hctx_rtotimer.data     = (unsigned long)sk;

diff --git a/net/dccp/ccids/ccid2.h b/net/dccp/ccids/ccid2.h
index 2a02ce04ba85dc0fada730a6de24efd5b47c9004..5b2ef4acb300de407396a90d7a4f7208b2a85d63 100644 (file)
--- a/net/dccp/ccids/ccid2.h
+++ b/net/dccp/ccids/ccid2.h
@@ -71,6 +71,7 @@ struct ccid2_hc_tx_sock {
        u64                     ccid2hctx_rpseq;
        int                     ccid2hctx_rpdupack;
        int                     ccid2hctx_sendwait;
+       unsigned long           ccid2hctx_last_cong;
 };
 
 struct ccid2_hc_rx_sock {