[CCID 3]: Inline for moving average
The moving average computation occurs so frequently in the CCID 3 code that
it merits an inline function of its own. This is built on a suggestion by
Arnaldo in http://www.mail-archive.com/[email protected]/msg01662.html
Notes:
------
1. The RTT estimate from the SYN exchange is now used when it is available,
increasing initial accuracy of RTT estimator.
2. Shortened the statement for updating `s' a bit.
Signed-off-by: Gerrit Renker <[EMAIL PROTECTED]>
---
net/dccp/ccids/ccid3.c | 25 +++++--------------------
net/dccp/ccids/lib/tfrc.h | 9 +++++++++
2 files changed, 14 insertions(+), 20 deletions(-)
--- a/net/dccp/ccids/lib/tfrc.h
+++ b/net/dccp/ccids/lib/tfrc.h
@@ -37,6 +37,15 @@ static inline u32 scaled_div32(u64 a, u3
return result;
}
+/**
+ * tfrc_ewma - Exponentially weighted moving average
+ * @weight: Weight to be used as damping factor, in units of 1/10
+ */
+static inline u32 tfrc_ewma(const u32 avg, const u32 newval, const u8 weight)
+{
+ return avg? (weight * avg + (10 - weight) * newval) / 10 : newval;
+}
+
extern u32 tfrc_calc_x(u16 s, u32 R, u32 p);
extern u32 tfrc_calc_x_reverse_lookup(u32 fvalue);
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -188,7 +188,7 @@ static inline void ccid3_hc_tx_update_s(
{
const u16 old_s = hctx->ccid3hctx_s;
- hctx->ccid3hctx_s = old_s == 0 ? len : (9 * old_s + len) / 10;
+ hctx->ccid3hctx_s = tfrc_ewma(hctx->ccid3hctx_s, len, 9);
if (hctx->ccid3hctx_s != old_s)
ccid3_update_send_interval(hctx);
@@ -461,25 +461,15 @@ static void ccid3_hc_tx_packet_recv(stru
dccp_timestamp(sk, &now);
/*
- * Calculate new round trip sample as per [RFC 3448, 4.3] by
- * R_sample = (now - t_recvdata) - t_elapsed
+ * Calculate new RTT sample and update moving average
*/
r_sample = dccp_sample_rtt(sk, &now, &packet->dccphtx_tstamp);
+ hctx->ccid3hctx_rtt = tfrc_ewma(hctx->ccid3hctx_rtt, r_sample,
9);
- /*
- * Update RTT estimate by
- * If (No feedback recv)
- * R = R_sample;
- * Else
- * R = q * R + (1 - q) * R_sample;
- *
- * q is a constant, RFC 3448 recomments 0.9
- */
if (hctx->ccid3hctx_state == TFRC_SSTATE_NO_FBACK) {
/*
* Larger Initial Windows [RFC 4342, sec. 5]
*/
- hctx->ccid3hctx_rtt = r_sample;
hctx->ccid3hctx_x = rfc3390_initial_rate(sk);
hctx->ccid3hctx_t_ld = now;
@@ -493,8 +483,6 @@ static void ccid3_hc_tx_packet_recv(stru
ccid3_hc_tx_set_state(sk, TFRC_SSTATE_FBACK);
} else {
- hctx->ccid3hctx_rtt = (9 * hctx->ccid3hctx_rtt +
- r_sample) / 10;
/* Update sending rate (step 4 of [RFC 3448, 4.3]) */
if (hctx->ccid3hctx_p > 0)
@@ -720,11 +708,8 @@ static void ccid3_hc_rx_set_state(struct
static inline void ccid3_hc_rx_update_s(struct ccid3_hc_rx_sock *hcrx, int len)
{
- if (unlikely(len == 0)) /* don't update on empty packets (e.g. ACKs) */
- ccid3_pr_debug("Packet payload length is 0 - not updating\n");
- else
- hcrx->ccid3hcrx_s = hcrx->ccid3hcrx_s == 0 ? len :
- (9 * hcrx->ccid3hcrx_s + len) / 10;
+ if (likely(len > 0)) /* don't update on empty packets (e.g. ACKs) */
+ hcrx->ccid3hcrx_s = tfrc_ewma(hcrx->ccid3hcrx_s, len, 9);
}
static void ccid3_hc_rx_send_feedback(struct sock *sk)
-
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