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bug #50476: initialize ssthresh to TCP_SND_BUF

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This commit changes ssthresh to be the largest effective congestion
window (amount of in-flight data). This follows the guidance of RFC
5681 which recommends setting ssthresh arbitrarily high.

LwIP was previously using the receive window value at the end of the
3-way handshake and in the case of an active open where the receiver
used window scaling and/or window auto-tuning, this resulted in a very
small ssthresh value even though the window ramped up once the connection
was established

(cherry picked from commit b90a54f989)
This commit is contained in:
Joel Cunningham
2017-03-07 20:53:02 -06:00
committed by goldsimon
parent 2848b17e80
commit 2452bc9336
2 changed files with 8 additions and 12 deletions
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11
src/core/tcp_in.c
View File

@@ -61,8 +61,6 @@
/** Initial CWND calculation as defined RFC 2581 */
#define LWIP_TCP_CALC_INITIAL_CWND(mss) LWIP_MIN((4U * (mss)), LWIP_MAX((2U * (mss)), 4380U));
/** Initial slow start threshold value: we use the full window */
#define LWIP_TCP_INITIAL_SSTHRESH(pcb) ((pcb)->snd_wnd)
/* These variables are global to all functions involved in the input
processing of TCP segments. They are set by the tcp_input()
@@ -615,7 +613,6 @@ tcp_listen_input(struct tcp_pcb_listen *pcb)
tcp_parseopt(npcb);
npcb->snd_wnd = tcphdr->wnd;
npcb->snd_wnd_max = npcb->snd_wnd;
npcb->ssthresh = LWIP_TCP_INITIAL_SSTHRESH(npcb);
#if TCP_CALCULATE_EFF_SEND_MSS
npcb->mss = tcp_eff_send_mss(npcb->mss, &npcb->local_ip, &npcb->remote_ip);
@@ -771,9 +768,6 @@ tcp_process(struct tcp_pcb *pcb)
pcb->mss = tcp_eff_send_mss(pcb->mss, &pcb->local_ip, &pcb->remote_ip);
#endif /* TCP_CALCULATE_EFF_SEND_MSS */
/* Set ssthresh again after changing 'mss' and 'snd_wnd' */
pcb->ssthresh = LWIP_TCP_INITIAL_SSTHRESH(pcb);
pcb->cwnd = LWIP_TCP_CALC_INITIAL_CWND(pcb->mss);
LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_process (SENT): cwnd %"TCPWNDSIZE_F
" ssthresh %"TCPWNDSIZE_F"\n",
@@ -855,11 +849,6 @@ tcp_process(struct tcp_pcb *pcb)
* we'd better pass it on to the application as well. */
tcp_receive(pcb);
/* passive open: update initial ssthresh now that the correct window is
known: if the remote side supports window scaling, the window sent
with the initial SYN can be smaller than the one used later */
pcb->ssthresh = LWIP_TCP_INITIAL_SSTHRESH(pcb);
/* Prevent ACK for SYN to generate a sent event */
if (recv_acked != 0) {
recv_acked--;