dccp tfrc: Perform early loss detection
This enables the TFRC code to begin loss detection (as soon as the module
is loaded), using the latest updates from rfc3448bis-06, 6.3.1:
* when the first data packet(s) are lost or marked, set
* X_target = s/(2*R) => f(p) = s/(R * X_target) = 2,
* corresponding to a loss rate of ~ 20.64%.
The handle_loss() function is now called right at the begin of rx_packet_recv()
and thus no longer protected against duplicates: hence a call to rx_duplicate()
has been added. Such a call makes sense now, as the previous patch initialises
the first entry with a sequence number of GSR.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index 36f4992..0a7c225 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -577,6 +577,28 @@
hcrx->p_inverse = ~0U; /* see RFC 4342, 8.5 */
break;
case CCID3_FBACK_PARAM_CHANGE:
+ if (unlikely(hcrx->state == TFRC_RSTATE_NO_DATA)) {
+ /*
+ * rfc3448bis-06, 6.3.1: First packet(s) lost or marked
+ * FIXME: in rfc3448bis the receiver returns X_recv=0
+ * here as it normally would in the first feedback packet.
+ * However this is not possible yet, since the code still
+ * uses RFC 3448, i.e.
+ * If (p > 0)
+ * Calculate X_calc using the TCP throughput equation.
+ * X = max(min(X_calc, 2*X_recv), s/t_mbi);
+ * would bring X down to s/t_mbi. That is why we return
+ * X_recv according to rfc3448bis-06 for the moment.
+ */
+ u32 rtt = hcrx->rtt ? : DCCP_FALLBACK_RTT, s = hcrx->s;
+
+ if (s == 0) {
+ DCCP_WARN("No sample for s, using fallback\n");
+ s = TCP_MIN_RCVMSS;
+ }
+ hcrx->x_recv = scaled_div32(s, 2 * rtt);
+ break;
+ }
/*
* When parameters change (new loss or p > p_prev), we do not
* have a reliable estimate for R_m of [RFC 3448, 6.2] and so
@@ -650,6 +672,14 @@
u32 x_recv, p, delta;
u64 fval;
+ /*
+ * rfc3448bis-06, 6.3.1: First data packet(s) are marked or lost. Set p
+ * to give the equivalent of X_target = s/(2*R). Thus fval = 2 and so p
+ * is about 20.64%. This yields an interval length of 4.84 (rounded up).
+ */
+ if (unlikely(hcrx->state == TFRC_RSTATE_NO_DATA))
+ return 5;
+
if (hcrx->rtt == 0) {
DCCP_WARN("No RTT estimate available, using fallback RTT\n");
hcrx->rtt = DCCP_FALLBACK_RTT;
@@ -683,6 +713,15 @@
const u64 ndp = dccp_sk(sk)->dccps_options_received.dccpor_ndp;
const bool is_data_packet = dccp_data_packet(skb);
+ /*
+ * Perform loss detection and handle pending losses
+ */
+ if (tfrc_rx_handle_loss(&hcrx->hist, &hcrx->li_hist,
+ skb, ndp, ccid3_first_li, sk)) {
+ do_feedback = CCID3_FBACK_PARAM_CHANGE;
+ goto done_receiving;
+ }
+
if (unlikely(hcrx->state == TFRC_RSTATE_NO_DATA)) {
if (is_data_packet) {
const u32 payload = skb->len - dccp_hdr(skb)->dccph_doff * 4;
@@ -710,15 +749,6 @@
hcrx->bytes_recv += payload;
}
- /*
- * Perform loss detection and handle pending losses
- */
- if (tfrc_rx_handle_loss(&hcrx->hist, &hcrx->li_hist,
- skb, ndp, ccid3_first_li, sk)) {
- do_feedback = CCID3_FBACK_PARAM_CHANGE;
- goto done_receiving;
- }
-
if (tfrc_rx_hist_loss_pending(&hcrx->hist))
return; /* done receiving */