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dccp ccid-2: prevent cwnd > Sequence Window 

Add a check to prevent CCID-2 from increasing the cwnd 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 the 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 <sj323707@ohio.edu>
Acked-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
This commit is contained in:
Samuel Jero 2011-07-24 20:49:19 -06:00 committed by Gerrit Renker
parent 31daf0393f
commit d346d886a4
2 changed files with 40 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

48
net/dccp/ccids/ccid2.c
View File

@ -85,7 +85,6 @@ static int ccid2_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
static void ccid2_change_l_ack_ratio(struct sock *sk, u32 val)
{
struct dccp_sock *dp = dccp_sk(sk);
u32 max_ratio = DIV_ROUND_UP(ccid2_hc_tx_sk(sk)->tx_cwnd, 2);
/*
@ -98,14 +97,15 @@ static void ccid2_change_l_ack_ratio(struct sock *sk, u32 val)
DCCP_WARN("Limiting Ack Ratio (%u) to %u\n", val, max_ratio);
val = max_ratio;
}
if (val > DCCPF_ACK_RATIO_MAX)
val = DCCPF_ACK_RATIO_MAX;
dccp_feat_signal_nn_change(sk, DCCPF_ACK_RATIO,
min_t(u32, val, DCCPF_ACK_RATIO_MAX));
}
if (val == dp->dccps_l_ack_ratio)
return;
ccid2_pr_debug("changing local ack ratio to %u\n", val);
dp->dccps_l_ack_ratio = val;
static void ccid2_change_l_seq_window(struct sock *sk, u64 val)
{
dccp_feat_signal_nn_change(sk, DCCPF_SEQUENCE_WINDOW,
clamp_val(val, DCCPF_SEQ_WMIN,
DCCPF_SEQ_WMAX));
}
static void ccid2_hc_tx_rto_expire(unsigned long data)
@ -405,17 +405,37 @@ 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);
struct dccp_sock *dp = dccp_sk(sk);
int r_seq_used = hc->tx_cwnd / dp->dccps_l_ack_ratio;
if (hc->tx_cwnd < hc->tx_ssthresh) {
if (*maxincr > 0 && ++hc->tx_packets_acked == 2) {
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;
*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;
}
/*
* 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).

6
net/dccp/ccids/ccid2.h
View File

@ -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