[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 93a30ae..b88da03 100644
--- a/net/dccp/ccids/ccid2.c
+++ b/net/dccp/ccids/ccid2.c
@@ -187,10 +187,8 @@
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 @@
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 @@
/* 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 @@
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 @@
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 @@
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 @@
!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 @@
/* 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 @@
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 @@
{
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 @@
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 2a02ce0..5b2ef4a 100644
--- a/net/dccp/ccids/ccid2.h
+++ b/net/dccp/ccids/ccid2.h
@@ -71,6 +71,7 @@
u64 ccid2hctx_rpseq;
int ccid2hctx_rpdupack;
int ccid2hctx_sendwait;
+ unsigned long ccid2hctx_last_cong;
};
struct ccid2_hc_rx_sock {