[DCCP]: Reuse ktime_get_real() calls again
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>
diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
index e75efe7..e16f9bb 100644
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -113,27 +113,24 @@
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 @@
(((__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 @@
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 @@
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",