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tcp: task #14128 - Appropriate Byte Counting support

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This commit adds TCP Appropriate Byte Counting (ABC) support based on
RFC 3465

ABC replaces the previous congestion window growth mechanism and has been
configured with limit of 2 SMSS.  See task #14128 for discussion on
defaults, but the goal is to mitigate the performance impact of delayed
ACKs on congestion window growth

This commit also introduces a mechanism to track when the stack is
undergoing a period following an RTO where data is being retransmitted.

Lastly, this adds a unit test to verify RTO period tracking and some
basic ABC cwnd checking
This commit is contained in:
Joel Cunningham
2017-04-12 19:29:38 -05:00
parent e1f2c8b30c
commit de90d03e48
5 changed files with 171 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

1
src/core/tcp.c
View File

@@ -1100,6 +1100,7 @@ tcp_slowtmr_start:
LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_slowtmr: cwnd %"TCPWNDSIZE_F
" ssthresh %"TCPWNDSIZE_F"\n",
pcb->cwnd, pcb->ssthresh));
pcb->bytes_acked = 0;
/* The following needs to be called AFTER cwnd is set to one
mss - STJ */

39
src/core/tcp_in.c
View File

@@ -1103,6 +1103,7 @@ tcp_receive(struct tcp_pcb *pcb)
}
} else if (TCP_SEQ_BETWEEN(ackno, pcb->lastack+1, pcb->snd_nxt)) {
/* We come here when the ACK acknowledges new data. */
tcpwnd_size_t acked;
/* Reset the "IN Fast Retransmit" flag, since we are no longer
in fast retransmit. Also reset the congestion window to the
@@ -1110,6 +1111,7 @@ tcp_receive(struct tcp_pcb *pcb)
if (pcb->flags & TF_INFR) {
pcb->flags &= ~TF_INFR;
pcb->cwnd = pcb->ssthresh;
pcb->bytes_acked = 0;
}
/* Reset the number of retransmissions. */
@@ -1118,6 +1120,9 @@ tcp_receive(struct tcp_pcb *pcb)
/* Reset the retransmission time-out. */
pcb->rto = (pcb->sa >> 3) + pcb->sv;
/* Record how much data this ACK acks */
acked = (tcpwnd_size_t)(ackno - pcb->lastack);
/* Reset the fast retransmit variables. */
pcb->dupacks = 0;
pcb->lastack = ackno;
@@ -1126,12 +1131,25 @@ tcp_receive(struct tcp_pcb *pcb)
ssthresh). */
if (pcb->state >= ESTABLISHED) {
if (pcb->cwnd < pcb->ssthresh) {
if ((tcpwnd_size_t)(pcb->cwnd + pcb->mss) > pcb->cwnd) {
pcb->cwnd += pcb->mss;
tcpwnd_size_t increase;
/* limit to 1 SMSS segment during period following RTO */
u8_t num_seg = (pcb->flags & TF_RTO) ? 1 : 2;
/* RFC 3465, section 2.2 Slow Start */
increase = LWIP_MIN(acked, (tcpwnd_size_t)(num_seg * pcb->mss));
if (pcb->cwnd + increase > pcb->cwnd) {
pcb->cwnd += increase;
}
LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_receive: slow start cwnd %"TCPWNDSIZE_F"\n", pcb->cwnd));
} else {
tcpwnd_size_t new_cwnd = (pcb->cwnd + pcb->mss * pcb->mss / pcb->cwnd);
tcpwnd_size_t new_cwnd = pcb->cwnd;
/* RFC 3465, section 2.1 Congestion Avoidance */
if (pcb->bytes_acked + acked > pcb->bytes_acked) {
pcb->bytes_acked += acked;
if (pcb->bytes_acked >= pcb->cwnd) {
pcb->bytes_acked -= pcb->cwnd;
new_cwnd = pcb->cwnd + pcb->mss;
}
}
if (new_cwnd > pcb->cwnd) {
pcb->cwnd = new_cwnd;
}
@@ -1222,6 +1240,21 @@ tcp_receive(struct tcp_pcb *pcb)
}
}
pcb->snd_buf += recv_acked;
/* check if this ACK ends our retransmission of in-flight data */
if (pcb->flags & TF_RTO) {
/* RTO is done if
1) both queues are empty or
2) unacked is empty and unsent head contains data not part of RTO or
3) unacked head contains data not part of RTO */
if (pcb->unacked == NULL) {
if ((pcb->unsent == NULL) ||
(TCP_SEQ_LEQ(pcb->rto_end, lwip_ntohl(pcb->unsent->tcphdr->seqno)))) {
pcb->flags &= ~TF_RTO;
}
} else if (TCP_SEQ_LEQ(pcb->rto_end, lwip_ntohl(pcb->unacked->tcphdr->seqno))) {
pcb->flags &= ~TF_RTO;
}
}
/* End of ACK for new data processing. */
} else {
/* Out of sequence ACK, didn't really ack anything */

5
src/core/tcp_out.c
View File

@@ -1419,6 +1419,11 @@ tcp_rexmit_rto(struct tcp_pcb *pcb)
/* unacked queue is now empty */
pcb->unacked = NULL;
/* Mark RTO in-progress */
pcb->flags |= TF_RTO;
/* Record the next byte following retransmit */
pcb->rto_end = lwip_ntohl(seg->tcphdr->seqno) + TCP_TCPLEN(seg);
/* increment number of retransmissions */
if (pcb->nrtx < 0xFF) {
++pcb->nrtx;