This updates the TFRC loss intervals code, which so far could only support
lost packets, to also handle the case of ECN-marked-CE packets:
* the begin and length of the loss interval are different;
* there are combinations of loss + ECN-marked-CE which the code does not
currently consider (it is not worth the complexity), comments have been
added to point this out.
Further changes:
----------------
The implementation of the "is the loss interval already closed?" check as per
RFC 4342, 10.2 has been improved to test the condition more efficiently.
Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx>
---
net/dccp/ccids/lib/loss_interval.c | 76 ++++++++++++++++++++++++++++--------
1 files changed, 59 insertions(+), 17 deletions(-)
--- a/net/dccp/ccids/lib/loss_interval.c
+++ b/net/dccp/ccids/lib/loss_interval.c
@@ -124,12 +124,12 @@ void tfrc_lh_update_i_mean(struct tfrc_loss_hist *lh, struct sk_buff *skb)
tfrc_lh_calc_i_mean(lh);
}
-/* Determine if `new_loss' does begin a new loss interval [RFC 4342, 10.2] */
-static inline u8 tfrc_lh_is_new_loss(struct tfrc_loss_interval *cur,
- struct tfrc_rx_hist_entry *new_loss)
+/* RFC 4342, 10.2: test for the existence of packet with sequence number S */
+static bool tfrc_lh_closed_check(struct tfrc_loss_interval *cur, const u8 ccval)
{
- return dccp_delta_seqno(cur->li_seqno, new_loss->tfrchrx_seqno) > 0 &&
- (cur->li_is_closed || SUB16(new_loss->tfrchrx_ccval, cur->li_ccval) > 4);
+ if (SUB16(ccval, cur->li_ccval) > 4)
+ cur->li_is_closed = true;
+ return cur->li_is_closed;
}
/** tfrc_lh_interval_add - Insert new record into the Loss Interval database
@@ -142,27 +142,69 @@ static inline u8 tfrc_lh_is_new_loss(struct tfrc_loss_interval *cur,
bool tfrc_lh_interval_add(struct tfrc_loss_hist *lh, struct tfrc_rx_hist *rh,
u32 (*calc_first_li)(struct sock *), struct sock *sk)
{
- struct tfrc_loss_interval *cur = tfrc_lh_peek(lh), *new;
+ struct tfrc_loss_interval *cur = tfrc_lh_peek(lh);
+ struct tfrc_rx_hist_entry *cong_evt;
+ u64 cong_evt_seqno;
+
+ /*
+ * Determine if the new event is caused by a lost or ECN-marked packet.
+ * Both events can coincide (e.g. if the third packet after a loss is
+ * marked as CE). We avoid the complexity caused by such mixed cases:
+ * 1) if the cause is a lost packet, we do not check whether it is
+ * also an ECN-marked packet (not necessary);
+ * 2) calling this routine with a loss_count of 0..NDUPACK-1 implies
+ * that the cause is an ECN-marked-CE packet.
+ * FIXME: if in this case the loss_count is not 0, loss tracking is
+ * reset. This is a complex corner case (see packet_history.c) and
+ * hence currently not supported.
+ */
+ if (rh->loss_count == TFRC_NDUPACK) {
+ /*
+ * The sequence number of the first packet known to be lost is
+ * the successor of the last packet received before the gap.
+ */
+ cong_evt = tfrc_rx_hist_loss_prev(rh);
+ cong_evt_seqno = ADD48(cong_evt->tfrchrx_seqno, 1);
+ } else {
+ /*
+ * ECN-marked packet. Since ECN-marks are reported as soon as a
+ * packet is delivered, it is stored in the last-received entry.
+ */
+ cong_evt = tfrc_rx_hist_last_rcv(rh);
+ cong_evt_seqno = cong_evt->tfrchrx_seqno;
+ }
- if (cur != NULL && !tfrc_lh_is_new_loss(cur, tfrc_rx_hist_loss_prev(rh)))
- return false;
+ /* Test if this event starts a new loss interval */
+ if (cur != NULL) {
+ s64 len = dccp_delta_seqno(cur->li_seqno, cong_evt_seqno);
+ if (len <= 0)
+ return false;
+
+ if (!tfrc_lh_closed_check(cur, cong_evt->tfrchrx_ccval))
+ return false;
- new = tfrc_lh_demand_next(lh);
- if (unlikely(new == NULL)) {
+ /* RFC 5348, 5.3: length between subsequent intervals */
+ cur->li_length = len;
+ }
+
+ /* Make the new interval the current one */
+ cur = tfrc_lh_demand_next(lh);
+ if (unlikely(cur == NULL)) {
DCCP_CRIT("Cannot allocate/add loss record.");
return false;
}
- new->li_seqno = tfrc_rx_hist_loss_prev(rh)->tfrchrx_seqno;
- new->li_ccval = tfrc_rx_hist_loss_prev(rh)->tfrchrx_ccval;
- new->li_is_closed = 0;
+ cur->li_seqno = cong_evt_seqno;
+ cur->li_ccval = cong_evt->tfrchrx_ccval;
+ cur->li_is_closed = false;
if (++lh->counter == 1)
- lh->i_mean = new->li_length = (*calc_first_li)(sk);
+ lh->i_mean = cur->li_length = (*calc_first_li)(sk);
else {
- cur->li_length = dccp_delta_seqno(cur->li_seqno, new->li_seqno);
- new->li_length = dccp_delta_seqno(new->li_seqno,
- tfrc_rx_hist_last_rcv(rh)->tfrchrx_seqno) + 1;
+ /* RFC 5348, 5.3: length of the open loss interval I_0 */
+ cur->li_length = dccp_delta_seqno(cur->li_seqno,
+ tfrc_rx_hist_last_rcv(rh)->tfrchrx_seqno) + 1;
+
if (lh->counter > (2*LIH_SIZE))
lh->counter -= LIH_SIZE;
--
1.6.0.rc2
--
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