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tcp_out rto: delay re-transmission earlier if link writes are deferred.

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There is already a guard in tcp_output_segment() for a pbuf still being
referenced by the netif driver due to deferred transmission, however the callers
are modifying state even when this gives up.

It seems cleaner to have the callers guard this case and avoid modifying their
state.

tcp_rexmit_rto() might better avoid re-transmission of any segments if any of
the unacked segments are deferred, to avoid loading the link further if it is
struggling to flush its buffered writes. Link level queues can be limited on
some devices and need spares for link management.
This commit is contained in:
Our Air Quality 2017-08-05 19:18:21 +10:00 committed by goldsimon
parent 902d393aef
commit 6a01607004
1 changed files with 26 additions and 1 deletions
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27
src/core/tcp_out.c
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@ -1523,6 +1523,16 @@ tcp_rexmit_rto(struct tcp_pcb *pcb)
return;
}
/* Give up if any of the segment pbufs are still referenced by the netif
driver due to deferred transmission. No point loading the link further if
it is struggling to flush its buffered writes. */
for (seg = pcb->unacked; seg != NULL; seg = seg->next) {
if (seg->p->ref != 1) {
LWIP_DEBUGF(TCP_RTO_DEBUG, ("tcp_rexmit_rto busy\n"));
return;
}
}
/* Move all unacked segments to the head of the unsent queue */
for (seg = pcb->unacked; seg->next != NULL; seg = seg->next);
/* concatenate unsent queue after unacked queue */
@ -1572,9 +1582,17 @@ tcp_rexmit(struct tcp_pcb *pcb)
return;
}
seg = pcb->unacked;
/* Give up if the first segment pbuf is still referenced by the netif driver
due to deferred transmission. */
if (seg->p->ref != 1) {
LWIP_DEBUGF(TCP_RTO_DEBUG, ("tcp_rexmit busy\n"));
return;
}
/* Move the first unacked segment to the unsent queue */
/* Keep the unsent queue sorted. */
seg = pcb->unacked;
pcb->unacked = seg->next;
cur_seg = &(pcb->unsent);
@ -1614,6 +1632,13 @@ void
tcp_rexmit_fast(struct tcp_pcb *pcb)
{
if (pcb->unacked != NULL && !(pcb->flags & TF_INFR)) {
/* Give up if the first segment pbuf is still referenced by the netif driver
due to deferred transmission. */
if (pcb->unacked->p->ref != 1) {
LWIP_DEBUGF(TCP_RTO_DEBUG, ("tcp_rexmit_fast busy\n"));
return;
}
/* This is fast retransmit. Retransmit the first unacked segment. */
LWIP_DEBUGF(TCP_FR_DEBUG,
("tcp_receive: dupacks %"U16_F" (%"U32_F