This puts the window counter computation [RFC 4342, 8.1] into a separate
function which is called whenever a new packet is ready for immediate
transmission in ccid3_hc_tx_send_packet.
Justification:
The window counter update was previously computed after the packet was sent. This has
two drawbacks, both fixed by this patch:
1) re-compute another timestamp almost directly after the packet was sent (expensive),
2) the CCVal for the window counter is needed at the instant the packet is sent.
Further details:
The initialisation of the window counter is left in the state NO_SENT, as before.
The algorithm will do nothing if either RTT is initialised to 0 (which is ok) or if
the RTT value remains below 4 microseconds (which is almost pathological).
Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx>
Acked-by: Ian McDonald <ian.mcdonald@xxxxxxxxxxx>
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxxxx>
---
net/dccp/ccids/ccid3.c | 49 ++++++++++++++++++++++++++++--------------------
1 files changed, 29 insertions(+), 20 deletions(-)
diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index 122a716..1a2ffa1 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -161,6 +161,33 @@ static inline void ccid3_hc_tx_update_s(
*/
}
+/*
+ * Update Window Counter using the algorithm from [RFC 4342, 8.1].
+ * The algorithm is not applicable if RTT < 4 microseconds.
+ */
+static inline void ccid3_hc_tx_update_win_count(struct ccid3_hc_tx_sock *hctx,
+ struct timeval *now)
+{
+ suseconds_t delta;
+ u32 quarter_rtts;
+
+ if (unlikely(hctx->ccid3hctx_rtt < 4)) /* avoid divide-by-zero */
+ return;
+
+ delta = timeval_delta(now, &hctx->ccid3hctx_t_last_win_count);
+ DCCP_BUG_ON(delta < 0);
+
+ quarter_rtts = (u32)delta / (hctx->ccid3hctx_rtt / 4);
+
+ if (quarter_rtts > 0) {
+ hctx->ccid3hctx_t_last_win_count = *now;
+ hctx->ccid3hctx_last_win_count += min_t(u32, quarter_rtts, 5);
+ hctx->ccid3hctx_last_win_count &= 0xF; /* mod 16 */
+
+ ccid3_pr_debug("now at %#X\n", hctx->ccid3hctx_last_win_count);
+ }
+}
+
static void ccid3_hc_tx_no_feedback_timer(unsigned long data)
{
struct sock *sk = (struct sock *)data;
@@ -333,6 +360,8 @@ static int ccid3_hc_tx_send_packet(struc
*/
if (delay - (suseconds_t)hctx->ccid3hctx_delta >= 0)
return delay / 1000L;
+
+ ccid3_hc_tx_update_win_count(hctx, &now);
break;
case TFRC_SSTATE_TERM:
DCCP_BUG("Illegal %s state TERM, sk=%p", dccp_role(sk), sk);
@@ -353,7 +382,6 @@ static void ccid3_hc_tx_packet_sent(stru
const struct dccp_sock *dp = dccp_sk(sk);
struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
struct timeval now;
- suseconds_t quarter_rtt;
struct dccp_tx_hist_entry *packet;
BUG_ON(hctx == NULL);
@@ -373,25 +401,6 @@ static void ccid3_hc_tx_packet_sent(stru
}
packet->dccphtx_tstamp = now;
packet->dccphtx_seqno = dp->dccps_gss;
- /*
- * Check if win_count have changed
- * Algorithm in "8.1. Window Counter Value" in RFC 4342.
- */
- quarter_rtt = timeval_delta(&now, &hctx->ccid3hctx_t_last_win_count);
- if (likely(hctx->ccid3hctx_rtt > 8))
- quarter_rtt /= hctx->ccid3hctx_rtt / 4;
-
- if (quarter_rtt > 0) {
- hctx->ccid3hctx_t_last_win_count = now;
- hctx->ccid3hctx_last_win_count = (hctx->ccid3hctx_last_win_count +
- min_t(unsigned long, quarter_rtt, 5)) % 16;
- ccid3_pr_debug("%s, sk=%p, window changed from "
- "%u to %u!\n",
- dccp_role(sk), sk,
- packet->dccphtx_ccval,
- hctx->ccid3hctx_last_win_count);
- }
-
hctx->ccid3hctx_idle = 0;
packet->dccphtx_rtt = hctx->ccid3hctx_rtt;
packet->dccphtx_sent = 1;
--
1.4.2.1.g3d5c
-
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