[CCID 3] Consolidate handling of t_RTO
This patch
* removes setting t_RTO in ccid3_hc_tx_init (per [RFC 3448, 4.2], t_RTO is
undefined until feedback has been received);
* makes some trivial changes (updates of comments);
* performs a small optimisation by exploiting that the feedback timeout
uses the value of t_ipi. The way it is done is safe, because the timeouts
appear after the changes to t_ipi, ensuring that up-to-date values are used;
* in ccid3_hc_tx_packet_recv, moves the t_rto statement closer to the calculation
of the next_tmout. This makes the code clearer to read and is also safe, since
t_rto is not updated until the next call of ccid3_hc_tx_packet_recv, and is not
read by the functions called via ccid_wait_for_ccid();
* removes a `max' statement in sk_reset_timer, this is not needed since the timeout
value is always greater than 1E6 microseconds.
* adds `XXX'es to highlight that currently the nofeedback timer is set
in a non-standard way
Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx>
---
net/dccp/ccids/ccid3.c | 29 ++++++++++++++---------------
1 file changed, 14 insertions(+), 15 deletions(-)
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -244,11 +244,10 @@ static void ccid3_hc_tx_no_feedback_time
}
/*
* Schedule no feedback timer to expire in
- * max(4 * R, 2 * s / X)
+ * max(4 * t_RTO, 2 * s/X) = max(4 * t_RTO, 2 * t_ipi)
+ * XXX This is non-standard, RFC 3448, 4.3 uses 4 * R
*/
- next_tmout = max_t(u32, hctx->ccid3hctx_t_rto,
- 2 * usecs_div(hctx->ccid3hctx_s,
- hctx->ccid3hctx_x));
+ next_tmout = max(hctx->ccid3hctx_t_rto, 2*hctx->ccid3hctx_t_ipi);
break;
case TFRC_SSTATE_NO_SENT:
DCCP_BUG("Illegal %s state NO_SENT, sk=%p", dccp_role(sk), sk);
@@ -482,10 +481,6 @@ static void ccid3_hc_tx_packet_recv(stru
"r_sample=%us\n", dccp_role(sk), sk,
hctx->ccid3hctx_rtt, r_sample);
- /* Update timeout interval */
- hctx->ccid3hctx_t_rto = max_t(u32, 4 * hctx->ccid3hctx_rtt,
- USEC_PER_SEC);
-
/* Update receive rate */
hctx->ccid3hctx_x_recv = x_recv;/* X_recv in bytes per sec */
@@ -513,17 +508,22 @@ static void ccid3_hc_tx_packet_recv(stru
&hctx->ccid3hctx_hist, packet);
/*
* As we have calculated new ipi, delta, t_nom it is possible that
- * we now can send a packet, so wake up dccp_wait_for_ccids.
+ * we now can send a packet, so wake up dccp_wait_for_ccid
*/
sk->sk_write_space(sk);
+
+ /* Update timeout interval. We use the alternative variant of
+ * [RFC 3448, 3.1] which sets the upper bound of t_rto to one
+ * second, as it is suggested for TCP (see RFC 2988, 2.4). */
+ hctx->ccid3hctx_t_rto = max_t(u32, 4 * hctx->ccid3hctx_rtt,
+ USEC_PER_SEC );
/*
* Schedule no feedback timer to expire in
- * max(4 * R, 2 * s / X)
+ * max(4 * t_RTO, 2 * s/X) = max(4 * t_RTO, 2 * t_ipi)
+ * XXX This is non-standard, RFC 3448, 4.3 uses 4 * R
*/
- next_tmout = max(hctx->ccid3hctx_t_rto,
- 2 * usecs_div(hctx->ccid3hctx_s,
- hctx->ccid3hctx_x));
+ next_tmout = max(hctx->ccid3hctx_t_rto, 2*hctx->ccid3hctx_t_ipi);
ccid3_pr_debug("%s, sk=%p, Scheduled no feedback timer to "
"expire in %lu jiffies (%luus)\n",
@@ -531,7 +531,7 @@ static void ccid3_hc_tx_packet_recv(stru
usecs_to_jiffies(next_tmout), next_tmout);
sk_reset_timer(sk, &hctx->ccid3hctx_no_feedback_timer,
- jiffies + max_t(u32, 1, usecs_to_jiffies(next_tmout)));
+ jiffies + usecs_to_jiffies(next_tmout));
/* set idle flag */
hctx->ccid3hctx_idle = 1;
@@ -621,7 +621,6 @@ static int ccid3_hc_tx_init(struct ccid
struct ccid3_hc_tx_sock *hctx = ccid_priv(ccid);
hctx->ccid3hctx_s = 0;
- hctx->ccid3hctx_t_rto = USEC_PER_SEC;
hctx->ccid3hctx_state = TFRC_SSTATE_NO_SENT;
INIT_LIST_HEAD(&hctx->ccid3hctx_hist);
-
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