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[DCCP] ccid3: Two optimisations for sending rate recomputation

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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 <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
This commit is contained in:
Gerrit Renker 2006-12-10 00:00:14 -02:00 committed by David S. Miller
parent 45393a66a2
commit ff58629824
1 changed files with 16 additions and 11 deletions
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27
net/dccp/ccids/ccid3.c
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@ -138,9 +138,6 @@ static void ccid3_hc_tx_update_x(struct sock *sk, struct timeval *now)
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 sock *sk, struct timeval *now)
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_timer(unsigned long data)
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_timer(unsigned long data)
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(struct sock *sk, struct sk_buff *skb)
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, "