Add a check to prevent CCID 2 from increasing the Congestion Window
greater than the Sequence Window.
When the congestion window becomes bigger than the sequence window CCID
2 will attempt to keep more data in the network than the DCCP sequence
window code considers possible. This results in the sequence window code
issuing a sync, thereby inducing needless overhead. Further, if this
occurs at the sender, CCID 2 will never detect the problem because th
Acks it receives will indicate no losses. I have seen this cause a drop
of 1/3rd in throughput for a connection.
Also add code to adjust the sequence window to be about 5 times the
number of packets in the network (RFC 4340 7.5.2) and to adjust the Ack
Ratio so that the remote sequence window will hold about 5 times the
number of packets in the network. This allows the congestion window to
increase correctly without being limited by the sequence window.
---
Signed-off-by: Samuel Jero
diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c
--- a/net/dccp/ccids/ccid2.c
+++ b/net/dccp/ccids/ccid2.c
@@ -106,6 +106,27 @@ static void ccid2_change_l_ack_ratio(struct sock *sk, u32 val)
ccid2_pr_debug("changing local ack ratio to %u\n", val);
dp->dccps_l_ack_ratio = val;
+ dccp_feat_signal_nn_change(sk, DCCPF_ACK_RATIO, val);
+ return;
+}
+
+static void ccid2_change_l_seq_window(struct sock *sk, u64 val)
+{
+ struct dccp_sock *dp = dccp_sk(sk);
+
+ if (val < DCCPF_SEQ_WMIN)
+ val = DCCPF_SEQ_WMIN;
+
+ if (val > DCCPF_SEQ_WMAX)
+ val = DCCPF_SEQ_WMAX;
+
+ if (val == dp->dccps_l_seq_win)
+ return;
+
+ dp->dccps_l_seq_win = val;
+ dccp_feat_signal_nn_change(sk,
+ DCCPF_SEQUENCE_WINDOW, dp->dccps_l_seq_win);
+ return;
}
static void ccid2_hc_tx_rto_expire(unsigned long data)
@@ -418,17 +468,37 @@ static void ccid2_new_ack(struct sock *sk, struct ccid2_seq *seqp,
unsigned int *maxincr)
{
struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
-
- if (hc->tx_cwnd < hc->tx_ssthresh) {
- if (*maxincr > 0 && ++hc->tx_packets_acked == 2) {
- hc->tx_cwnd += 1;
- *maxincr -= 1;
- hc->tx_packets_acked = 0;
+ struct dccp_sock *dp = dccp_sk(sk);
+ int r_seq_used = hc->tx_cwnd/dp->dccps_l_ack_ratio;
+
+ if ((hc->tx_cwnd < dp->dccps_l_seq_win) &&
+ (r_seq_used < dp->dccps_r_seq_win)) {
+ if (hc->tx_cwnd < hc->tx_ssthresh) {
+ if (*maxincr > 0 && ++hc->tx_packets_acked == 2) {
+ hc->tx_cwnd += 1;
+ *maxincr -= 1;
+ hc->tx_packets_acked = 0;
+ }
+ } else if (++hc->tx_packets_acked >= hc->tx_cwnd) {
+ hc->tx_cwnd += 1;
+ hc->tx_packets_acked = 0;
}
- } else if (++hc->tx_packets_acked >= hc->tx_cwnd) {
- hc->tx_cwnd += 1;
- hc->tx_packets_acked = 0;
}
+
+ /*
+ * Adjust the local sequence window and the ack ratio to allow about
+ * 5 times the number of packets in the network (RFC 4340 7.5.2)
+ */
+ if (r_seq_used*CCID2_WIN_CHANGE_FACTOR >= dp->dccps_r_seq_win)
+ ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio*2);
+ else if (r_seq_used*CCID2_WIN_CHANGE_FACTOR < (dp->dccps_r_seq_win/2))
+ ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio/2 ? : 1U);
+
+ if (hc->tx_cwnd*CCID2_WIN_CHANGE_FACTOR >= dp->dccps_l_seq_win)
+ ccid2_change_l_seq_window(sk, dp->dccps_l_seq_win*2);
+ else if (hc->tx_cwnd*CCID2_WIN_CHANGE_FACTOR < (dp->dccps_l_seq_win/2))
+ ccid2_change_l_seq_window(sk, dp->dccps_l_seq_win/2);
+
/*
* FIXME: RTT is sampled several times per acknowledgment (for each
* entry in the Ack Vector), instead of once per Ack (as in TCP SACK).
diff --git a/net/dccp/ccids/ccid2.h b/net/dccp/ccids/ccid2.h
--- a/net/dccp/ccids/ccid2.h
+++ b/net/dccp/ccids/ccid2.h
@@ -43,6 +43,12 @@ struct ccid2_seq {
#define CCID2_SEQBUF_LEN 1024
#define CCID2_SEQBUF_MAX 128
+/*
+ * Multiple of congestion window to keep the sequence window at
+ * (RFC 4340 7.5.2)
+ */
+#define CCID2_WIN_CHANGE_FACTOR 5
+
/**
* struct ccid2_hc_tx_sock - CCID2 TX half connection
* @tx_{cwnd,ssthresh,pipe}: as per RFC 4341, section 5
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