[DCCP]: Two optimisations for sending rate recomputation
This performs two optimisations for the recomputation of the sending rate.
1) Currently the target sending rate X_calc is recalculated whenever
a) the nofeedback timer expires, or
b) a feedback packet is received.
In the (a) case, recomputing X_calc is redundant, since
* the parameters p and RTT do not change in between the
reception of feedback packets;
* the parameter X_recv is either modified from received
feedback or via the nofeedback timer;
* a test (`p == 0') in the nofeedback timer avoids using
a stale/undefined value of X_calc if p was previously 0.
2) The nofeedback timer now only recomputes a timestamp when p == 0.
This is according to step (4) of [RFC 3448, 4.3] and avoids
unnecessarily determining a timestamp.
A debug statement about not updating X is also removed - it helps very
little in debugging and just clutters the logs.
Signed-off-by: Gerrit Renker <[EMAIL PROTECTED]>
---
net/dccp/ccids/ccid3.c | 27 ++++++++++++++++-----------
1 file changed, 16 insertions(+), 11 deletions(-)
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -138,9 +138,6 @@ static void ccid3_hc_tx_update_x(struct
const __u32 old_x = hctx->ccid3hctx_x;
if (hctx->ccid3hctx_p > 0) {
- hctx->ccid3hctx_x_calc = tfrc_calc_x(hctx->ccid3hctx_s,
- hctx->ccid3hctx_rtt,
- hctx->ccid3hctx_p);
hctx->ccid3hctx_x = max_t(u32, min(hctx->ccid3hctx_x_calc,
hctx->ccid3hctx_x_recv * 2),
hctx->ccid3hctx_s / TFRC_T_MBI);
@@ -152,8 +149,7 @@ static void ccid3_hc_tx_update_x(struct
usecs_div(hctx->ccid3hctx_s,
hctx->ccid3hctx_rtt) );
hctx->ccid3hctx_t_ld = *now;
- } else
- ccid3_pr_debug("Not changing X\n");
+ }
if (hctx->ccid3hctx_x != old_x)
ccid3_update_send_time(hctx);
@@ -223,9 +219,11 @@ static void ccid3_hc_tx_no_feedback_time
ccid3_pr_debug("%s, sk=%p, state=%s, not idle\n",
dccp_role(sk), sk,
ccid3_tx_state_name(hctx->ccid3hctx_state));
- /* Halve sending rate */
- /* If (p == 0 || X_calc > 2 * X_recv)
+ /*
+ * Modify the cached value of X_recv [RFC 3448, 4.4]
+ *
+ * If (p == 0 || X_calc > 2 * X_recv)
* X_recv = max(X_recv / 2, s / (2 * t_mbi));
* Else
* X_recv = X_calc / 4;
@@ -233,14 +231,15 @@ static void ccid3_hc_tx_no_feedback_time
BUG_ON(hctx->ccid3hctx_p && !hctx->ccid3hctx_x_calc);
if (hctx->ccid3hctx_p == 0 ||
- hctx->ccid3hctx_x_calc > 2 * hctx->ccid3hctx_x_recv)
+ hctx->ccid3hctx_x_calc > 2 *
hctx->ccid3hctx_x_recv) {
hctx->ccid3hctx_x_recv = max_t(u32,
hctx->ccid3hctx_x_recv / 2,
hctx->ccid3hctx_s / (2 * TFRC_T_MBI));
- else
+ if (hctx->ccid3hctx_p == 0)
+ dccp_timestamp(sk, &now);
+ } else
hctx->ccid3hctx_x_recv = hctx->ccid3hctx_x_calc
/ 4;
- /* Update sending rate */
- dccp_timestamp(sk, &now);
+ /* Now recalculate X [RFC 3448, 4.3, step (4)] */
ccid3_hc_tx_update_x(sk, &now);
}
/*
@@ -496,6 +495,12 @@ static void ccid3_hc_tx_packet_recv(stru
hctx->ccid3hctx_rtt = (9 * hctx->ccid3hctx_rtt +
(u32)r_sample ) / 10;
+ /* Update sending rate (step 4 of [RFC 3448, 4.3]) */
+ if (hctx->ccid3hctx_p > 0)
+ hctx->ccid3hctx_x_calc =
+ tfrc_calc_x(hctx->ccid3hctx_s,
+ hctx->ccid3hctx_rtt,
+ hctx->ccid3hctx_p);
ccid3_hc_tx_update_x(sk, &now);
ccid3_pr_debug("%s(%p), RTT=%uus (sample=%ldus), s=%u, "
-
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