dccp ccid-3: Always perform receiver RTT sampling
This updates the CCID-3 receiver in part with regard to errata 610 and 611
(http://www.rfc-editor.org/errata_list.php), which change RFC 4342 to use the
Receive Rate as specified in rfc3448bis, requiring to constantly sample the
RTT (or use a sender RTT).
Doing this requires reusing the RX history structure after dealing with a loss.
The patch does not resolve how to compute X_recv if the interval is less
than 1 RTT. A FIXME has been added (and is resolved in subsequent patch).
Furthermore, since this is all TFRC-based functionality, the RTT estimation
is now also performed by the dccp_tfrc_lib module. This further simplifies
the CCID-3 code.
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 04b1835..8e64d966 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -556,8 +556,8 @@
* 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 = tfrc_rx_hist_packet_size(&hcrx->hist);
+ u32 s = tfrc_rx_hist_packet_size(&hcrx->hist),
+ rtt = tfrc_rx_hist_rtt(&hcrx->hist);
hcrx->x_recv = scaled_div32(s, 2 * rtt);
break;
@@ -576,6 +576,11 @@
break;
/* fall through */
case CCID3_FBACK_PERIODIC:
+ /*
+ * FIXME: check if delta is less than or equal to 1 RTT using
+ * the receiver RTT sample. This is described in Errata 610/611
+ * of RFC 4342 which reference section 6.2 of RFC 3448.
+ */
delta = ktime_us_delta(now, hcrx->tstamp_last_feedback);
if (delta <= 0)
DCCP_BUG("delta (%ld) <= 0", (long)delta);
@@ -633,8 +638,8 @@
static u32 ccid3_first_li(struct sock *sk)
{
struct ccid3_hc_rx_sock *hcrx = ccid3_hc_rx_sk(sk);
- u32 x_recv, p, delta,
- s = tfrc_rx_hist_packet_size(&hcrx->hist);
+ u32 s = tfrc_rx_hist_packet_size(&hcrx->hist),
+ rtt = tfrc_rx_hist_rtt(&hcrx->hist), x_recv, p, delta;
u64 fval;
/*
@@ -645,11 +650,6 @@
if (unlikely(hcrx->feedback == CCID3_FBACK_NONE))
return 5;
- if (hcrx->rtt == 0) {
- DCCP_WARN("No RTT estimate available, using fallback RTT\n");
- hcrx->rtt = DCCP_FALLBACK_RTT;
- }
-
delta = ktime_to_us(net_timedelta(hcrx->tstamp_last_feedback));
x_recv = scaled_div32(hcrx->hist.bytes_recvd, delta);
if (x_recv == 0) { /* would also trigger divide-by-zero */
@@ -661,7 +661,7 @@
x_recv = hcrx->x_recv;
}
- fval = scaled_div32(scaled_div(s, hcrx->rtt), x_recv);
+ fval = scaled_div32(scaled_div(s, rtt), x_recv);
p = tfrc_calc_x_reverse_lookup(fval);
ccid3_pr_debug("%s(%p), receive rate=%u bytes/s, implied "
@@ -696,25 +696,10 @@
return; /* done receiving */
/*
- * Handle data packets: RTT sampling and monitoring p
- */
- if (unlikely(!is_data_packet))
- goto update_records;
-
- if (!tfrc_lh_is_initialised(&hcrx->li_hist)) {
- const u32 sample = tfrc_rx_hist_sample_rtt(&hcrx->hist, skb);
- /*
- * Empty loss history: no loss so far, hence p stays 0.
- * Sample RTT values, since an RTT estimate is required for the
- * computation of p when the first loss occurs; RFC 3448, 6.3.1.
- */
- if (sample != 0)
- hcrx->rtt = tfrc_ewma(hcrx->rtt, sample, 9);
- }
- /*
* Check if the periodic once-per-RTT feedback is due; RFC 4342, 10.3
*/
- if (SUB16(dccp_hdr(skb)->dccph_ccval, hcrx->last_counter) > 3)
+ if (is_data_packet &&
+ SUB16(dccp_hdr(skb)->dccph_ccval, hcrx->last_counter) > 3)
do_feedback = CCID3_FBACK_PERIODIC;
update_records:
@@ -744,7 +729,7 @@
static void ccid3_hc_rx_get_info(struct sock *sk, struct tcp_info *info)
{
info->tcpi_options |= TCPI_OPT_TIMESTAMPS;
- info->tcpi_rcv_rtt = ccid3_hc_rx_sk(sk)->rtt;
+ info->tcpi_rcv_rtt = tfrc_rx_hist_rtt(&ccid3_hc_rx_sk(sk)->hist);
}
static int ccid3_hc_rx_getsockopt(struct sock *sk, const int optname, int len,
@@ -759,7 +744,7 @@
if (len < sizeof(rx_info))
return -EINVAL;
rx_info.tfrcrx_x_recv = hcrx->x_recv;
- rx_info.tfrcrx_rtt = hcrx->rtt;
+ rx_info.tfrcrx_rtt = tfrc_rx_hist_rtt(&hcrx->hist);
rx_info.tfrcrx_p = tfrc_invert_loss_event_rate(hcrx->p_inverse);
len = sizeof(rx_info);
val = &rx_info;