[CCID 3]: Wrap computation of RFC3390-initial rate into separate function
The CCID 3 and TFRC specs (RFC 4342, RFC 3448, draft-3448bis) make frequent
reference to the computation of the RFC-3390 initial sending rate:
1. Initial sending rate when RTT is known (RFC 4342, p. 6)
2. Response to Idle/Application-Limited periods (RFC 4342, 5.1)
This warrants putting the code into its own function, for later code reuse.
Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx>
---
net/dccp/ccids/ccid3.c | 24 ++++++++++++++++++------
1 file changed, 18 insertions(+), 6 deletions(-)
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -81,6 +81,21 @@ static void ccid3_hc_tx_set_state(struct
}
/*
+ * Compute the initial sending rate X_init according to RFC 3390:
+ * w_init = min(4 * MSS, max(2 * MSS, 4380 bytes))
+ * X_init = w_init / RTT
+ * For consistency with other parts of the code, X_init is scaled by 2^6.
+ */
+static inline u64 rfc3390_initial_rate(struct sock *sk)
+{
+ const struct dccp_sock *dp = dccp_sk(sk);
+ __u32 w_init = min(4 * dp->dccps_mss_cache,
+ max(2 * dp->dccps_mss_cache, 4380U));
+
+ return scaled_div(w_init << 6, ccid3_hc_tx_sk(sk)->ccid3hctx_rtt);
+}
+
+/*
* Recalculate t_ipi and delta (should be called whenver X changes)
*/
static inline void ccid3_update_send_interval(struct ccid3_hc_tx_sock *hctx)
@@ -471,19 +486,16 @@ static void ccid3_hc_tx_packet_recv(stru
/*
* Larger Initial Windows [RFC 4342, sec. 5]
*/
- __u32 w_init = min(4 * dp->dccps_mss_cache,
- max(2 * dp->dccps_mss_cache, 4380U));
hctx->ccid3hctx_rtt = r_sample;
- hctx->ccid3hctx_x = scaled_div(w_init << 6, r_sample);
+ hctx->ccid3hctx_x = rfc3390_initial_rate(sk);
hctx->ccid3hctx_t_ld = now;
ccid3_update_send_interval(hctx);
- ccid3_pr_debug("%s(%p), s=%u, MSS=%u, w_init=%u, "
+ ccid3_pr_debug("%s(%p), s=%u, MSS=%u, "
"R_sample=%dus, X=%llu\n", dccp_role(sk),
sk, hctx->ccid3hctx_s,
- dp->dccps_mss_cache, w_init,
- (int)r_sample,
+ dp->dccps_mss_cache, (int)r_sample,
hctx->ccid3hctx_x >> 6);
ccid3_hc_tx_set_state(sk, TFRC_SSTATE_FBACK);
-
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