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[DCCP]: Reuse ktime_get_real() calls again

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This patch reduces the number of timestamps taken in the receive path
for each packet.

The ccid3_hc_tx_update_x() routine is called in
 * the receive path for each CCID3-controlled packet
 * for the nofeedback timer (if no feedback arrives during 4 RTT)

Currently, when there is no loss, each packet gets timestamped twice.
The patch resolves this by recycling the first timestamp taken on packet
reception for RTT sampling.

When the no_feedback_timer() is called, then the timestamp argument is
simply set to NULL - so that ccid3_hc_tx_update_x() takes care of the logic.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Gerrit Renker 2007-09-25 22:39:16 -07:00 committed by David S. Miller
parent e0eb685962
commit aa97efd97a
1 changed files with 16 additions and 23 deletions
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39
net/dccp/ccids/ccid3.c
View File

@ -113,27 +113,24 @@ static inline void ccid3_update_send_interval(struct ccid3_hc_tx_sock *hctx)
hctx->ccid3hctx_s, (unsigned)(hctx->ccid3hctx_x >> 6));
}
/*
* Update X by
* If (p > 0)
* X_calc = calcX(s, R, p);
* X = max(min(X_calc, 2 * X_recv), s / t_mbi);
* Else
* If (now - tld >= R)
* X = max(min(2 * X, 2 * X_recv), s / R);
* tld = now;
/**
* ccid3_hc_tx_update_x - Update allowed sending rate X
* @stamp: most recent time if available - can be left NULL.
* This function tracks draft rfc3448bis, check there for latest details.
*
* Note: X and X_recv are both stored in units of 64 * bytes/second, to support
* fine-grained resolution of sending rates. This requires scaling by 2^6
* throughout the code. Only X_calc is unscaled (in bytes/second).
*
*/
static void ccid3_hc_tx_update_x(struct sock *sk)
static void ccid3_hc_tx_update_x(struct sock *sk, ktime_t *stamp)
{
struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
__u64 min_rate = 2 * hctx->ccid3hctx_x_recv;
const __u64 old_x = hctx->ccid3hctx_x;
ktime_t now = stamp? *stamp : ktime_get_real();
/*
* Handle IDLE periods: do not reduce below RFC3390 initial sending rate
@ -153,18 +150,14 @@ static void ccid3_hc_tx_update_x(struct sock *sk)
(((__u64)hctx->ccid3hctx_s) << 6) /
TFRC_T_MBI);
} else {
const ktime_t now = ktime_get_real();
} else if (ktime_us_delta(now, hctx->ccid3hctx_t_ld)
- (s64)hctx->ccid3hctx_rtt >= 0) {
if ((ktime_us_delta(now, hctx->ccid3hctx_t_ld) -
(s64)hctx->ccid3hctx_rtt) >= 0) {
hctx->ccid3hctx_x =
max(min(2 * hctx->ccid3hctx_x, min_rate),
scaled_div(((__u64)hctx->ccid3hctx_s) << 6,
hctx->ccid3hctx_rtt));
hctx->ccid3hctx_t_ld = now;
}
hctx->ccid3hctx_x =
max(min(2 * hctx->ccid3hctx_x, min_rate),
scaled_div(((__u64)hctx->ccid3hctx_s) << 6,
hctx->ccid3hctx_rtt));
hctx->ccid3hctx_t_ld = now;
}
if (hctx->ccid3hctx_x != old_x) {
@ -273,7 +266,7 @@ static void ccid3_hc_tx_no_feedback_timer(unsigned long data)
hctx->ccid3hctx_x_recv <<= 4;
}
/* Now recalculate X [RFC 3448, 4.3, step (4)] */
ccid3_hc_tx_update_x(sk);
ccid3_hc_tx_update_x(sk, NULL);
/*
* Schedule no feedback timer to expire in
* max(t_RTO, 2 * s/X) = max(t_RTO, 2 * t_ipi)
@ -493,7 +486,7 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
tfrc_calc_x(hctx->ccid3hctx_s,
hctx->ccid3hctx_rtt,
hctx->ccid3hctx_p);
ccid3_hc_tx_update_x(sk);
ccid3_hc_tx_update_x(sk, &now);
ccid3_pr_debug("%s(%p), RTT=%uus (sample=%uus), s=%u, "
"p=%u, X_calc=%u, X_recv=%u, X=%u\n",