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-rw-r--r--net/dccp/ccids/ccid2.c169
-rw-r--r--net/dccp/ccids/ccid2.h20
2 files changed, 108 insertions, 81 deletions
diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c
index f7f5069..7af3106 100644
--- a/net/dccp/ccids/ccid2.c
+++ b/net/dccp/ccids/ccid2.c
@@ -113,19 +113,12 @@ static void ccid2_change_l_ack_ratio(struct sock *sk, u32 val)
dp->dccps_l_ack_ratio = val;
}
-static void ccid2_change_srtt(struct ccid2_hc_tx_sock *hc, long val)
-{
- ccid2_pr_debug("change SRTT to %ld\n", val);
- hc->tx_srtt = val;
-}
-
static void ccid2_start_rto_timer(struct sock *sk);
static void ccid2_hc_tx_rto_expire(unsigned long data)
{
struct sock *sk = (struct sock *)data;
struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
- long s;
bh_lock_sock(sk);
if (sock_owned_by_user(sk)) {
@@ -137,10 +130,8 @@ static void ccid2_hc_tx_rto_expire(unsigned long data)
/* back-off timer */
hc->tx_rto <<= 1;
-
- s = hc->tx_rto / HZ;
- if (s > 60)
- hc->tx_rto = 60 * HZ;
+ if (hc->tx_rto > DCCP_RTO_MAX)
+ hc->tx_rto = DCCP_RTO_MAX;
ccid2_start_rto_timer(sk);
@@ -168,7 +159,7 @@ static void ccid2_start_rto_timer(struct sock *sk)
{
struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
- ccid2_pr_debug("setting RTO timeout=%ld\n", hc->tx_rto);
+ ccid2_pr_debug("setting RTO timeout=%u\n", hc->tx_rto);
BUG_ON(timer_pending(&hc->tx_rtotimer));
sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + hc->tx_rto);
@@ -339,9 +330,86 @@ static void ccid2_hc_tx_kill_rto_timer(struct sock *sk)
ccid2_pr_debug("deleted RTO timer\n");
}
-static inline void ccid2_new_ack(struct sock *sk,
- struct ccid2_seq *seqp,
- unsigned int *maxincr)
+/**
+ * ccid2_rtt_estimator - Sample RTT and compute RTO using RFC2988 algorithm
+ * This code is almost identical with TCP's tcp_rtt_estimator(), since
+ * - it has a higher sampling frequency (recommended by RFC 1323),
+ * - the RTO does not collapse into RTT due to RTTVAR going towards zero,
+ * - it is simple (cf. more complex proposals such as Eifel timer or research
+ * which suggests that the gain should be set according to window size),
+ * - in tests it was found to work well with CCID2 [gerrit].
+ */
+static void ccid2_rtt_estimator(struct sock *sk, const long mrtt)
+{
+ struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
+ long m = mrtt ? : 1;
+
+ if (hc->tx_srtt == 0) {
+ /* First measurement m */
+ hc->tx_srtt = m << 3;
+ hc->tx_mdev = m << 1;
+
+ hc->tx_mdev_max = max(TCP_RTO_MIN, hc->tx_mdev);
+ hc->tx_rttvar = hc->tx_mdev_max;
+ hc->tx_rtt_seq = dccp_sk(sk)->dccps_gss;
+ } else {
+ /* Update scaled SRTT as SRTT += 1/8 * (m - SRTT) */
+ m -= (hc->tx_srtt >> 3);
+ hc->tx_srtt += m;
+
+ /* Similarly, update scaled mdev with regard to |m| */
+ if (m < 0) {
+ m = -m;
+ m -= (hc->tx_mdev >> 2);
+ /*
+ * This neutralises RTO increase when RTT < SRTT - mdev
+ * (see P. Sarolahti, A. Kuznetsov,"Congestion Control
+ * in Linux TCP", USENIX 2002, pp. 49-62).
+ */
+ if (m > 0)
+ m >>= 3;
+ } else {
+ m -= (hc->tx_mdev >> 2);
+ }
+ hc->tx_mdev += m;
+
+ if (hc->tx_mdev > hc->tx_mdev_max) {
+ hc->tx_mdev_max = hc->tx_mdev;
+ if (hc->tx_mdev_max > hc->tx_rttvar)
+ hc->tx_rttvar = hc->tx_mdev_max;
+ }
+
+ /*
+ * Decay RTTVAR at most once per flight, exploiting that
+ * 1) pipe <= cwnd <= Sequence_Window = W (RFC 4340, 7.5.2)
+ * 2) AWL = GSS-W+1 <= GAR <= GSS (RFC 4340, 7.5.1)
+ * GAR is a useful bound for FlightSize = pipe.
+ * AWL is probably too low here, as it over-estimates pipe.
+ */
+ if (after48(dccp_sk(sk)->dccps_gar, hc->tx_rtt_seq)) {
+ if (hc->tx_mdev_max < hc->tx_rttvar)
+ hc->tx_rttvar -= (hc->tx_rttvar -
+ hc->tx_mdev_max) >> 2;
+ hc->tx_rtt_seq = dccp_sk(sk)->dccps_gss;
+ hc->tx_mdev_max = TCP_RTO_MIN;
+ }
+ }
+
+ /*
+ * Set RTO from SRTT and RTTVAR
+ * As in TCP, 4 * RTTVAR >= TCP_RTO_MIN, giving a minimum RTO of 200 ms.
+ * This agrees with RFC 4341, 5:
+ * "Because DCCP does not retransmit data, DCCP does not require
+ * TCP's recommended minimum timeout of one second".
+ */
+ hc->tx_rto = (hc->tx_srtt >> 3) + hc->tx_rttvar;
+
+ if (hc->tx_rto > DCCP_RTO_MAX)
+ hc->tx_rto = DCCP_RTO_MAX;
+}
+
+static void ccid2_new_ack(struct sock *sk, struct ccid2_seq *seqp,
+ unsigned int *maxincr)
{
struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
@@ -355,64 +423,15 @@ static inline void ccid2_new_ack(struct sock *sk,
hc->tx_cwnd += 1;
hc->tx_packets_acked = 0;
}
-
- /* update RTO */
- if (hc->tx_srtt == -1 ||
- time_after(jiffies, hc->tx_lastrtt + hc->tx_srtt)) {
- unsigned long r = (long)jiffies - (long)seqp->ccid2s_sent;
- int s;
-
- /* first measurement */
- if (hc->tx_srtt == -1) {
- ccid2_pr_debug("R: %lu Time=%lu seq=%llu\n",
- r, jiffies,
- (unsigned long long)seqp->ccid2s_seq);
- ccid2_change_srtt(hc, r);
- hc->tx_rttvar = r >> 1;
- } else {
- /* RTTVAR */
- long tmp = hc->tx_srtt - r;
- long srtt;
-
- if (tmp < 0)
- tmp *= -1;
-
- tmp >>= 2;
- hc->tx_rttvar *= 3;
- hc->tx_rttvar >>= 2;
- hc->tx_rttvar += tmp;
-
- /* SRTT */
- srtt = hc->tx_srtt;
- srtt *= 7;
- srtt >>= 3;
- tmp = r >> 3;
- srtt += tmp;
- ccid2_change_srtt(hc, srtt);
- }
- s = hc->tx_rttvar << 2;
- /* clock granularity is 1 when based on jiffies */
- if (!s)
- s = 1;
- hc->tx_rto = hc->tx_srtt + s;
-
- /* must be at least a second */
- s = hc->tx_rto / HZ;
- /* DCCP doesn't require this [but I like it cuz my code sux] */
-#if 1
- if (s < 1)
- hc->tx_rto = HZ;
-#endif
- /* max 60 seconds */
- if (s > 60)
- hc->tx_rto = HZ * 60;
-
- hc->tx_lastrtt = jiffies;
-
- ccid2_pr_debug("srtt: %ld rttvar: %ld rto: %ld (HZ=%d) R=%lu\n",
- hc->tx_srtt, hc->tx_rttvar,
- hc->tx_rto, HZ, r);
- }
+ /*
+ * FIXME: RTT is sampled several times per acknowledgment (for each
+ * entry in the Ack Vector), instead of once per Ack (as in TCP SACK).
+ * This causes the RTT to be over-estimated, since the older entries
+ * in the Ack Vector have earlier sending times.
+ * The cleanest solution is to not use the ccid2s_sent field at all
+ * and instead use DCCP timestamps: requires changes in other places.
+ */
+ ccid2_rtt_estimator(sk, jiffies - seqp->ccid2s_sent);
}
static void ccid2_congestion_event(struct sock *sk, struct ccid2_seq *seqp)
@@ -662,9 +681,7 @@ static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk)
if (ccid2_hc_tx_alloc_seq(hc))
return -ENOMEM;
- hc->tx_rto = 3 * HZ;
- ccid2_change_srtt(hc, -1);
- hc->tx_rttvar = -1;
+ hc->tx_rto = DCCP_TIMEOUT_INIT;
hc->tx_rpdupack = -1;
hc->tx_last_cong = jiffies;
setup_timer(&hc->tx_rtotimer, ccid2_hc_tx_rto_expire,
diff --git a/net/dccp/ccids/ccid2.h b/net/dccp/ccids/ccid2.h
index 1ec6a30..b017843 100644
--- a/net/dccp/ccids/ccid2.h
+++ b/net/dccp/ccids/ccid2.h
@@ -42,7 +42,12 @@ struct ccid2_seq {
* struct ccid2_hc_tx_sock - CCID2 TX half connection
* @tx_{cwnd,ssthresh,pipe}: as per RFC 4341, section 5
* @tx_packets_acked: Ack counter for deriving cwnd growth (RFC 3465)
- * @tx_lastrtt: time RTT was last measured
+ * @tx_srtt: smoothed RTT estimate, scaled by 2^3
+ * @tx_mdev: smoothed RTT variation, scaled by 2^2
+ * @tx_mdev_max: maximum of @mdev during one flight
+ * @tx_rttvar: moving average/maximum of @mdev_max
+ * @tx_rto: RTO value deriving from SRTT and RTTVAR (RFC 2988)
+ * @tx_rtt_seq: to decay RTTVAR at most once per flight
* @tx_rpseq: last consecutive seqno
* @tx_rpdupack: dupacks since rpseq
*/
@@ -55,11 +60,16 @@ struct ccid2_hc_tx_sock {
int tx_seqbufc;
struct ccid2_seq *tx_seqh;
struct ccid2_seq *tx_seqt;
- long tx_rto;
- long tx_srtt;
- long tx_rttvar;
- unsigned long tx_lastrtt;
+
+ /* RTT measurement: variables/principles are the same as in TCP */
+ u32 tx_srtt,
+ tx_mdev,
+ tx_mdev_max,
+ tx_rttvar,
+ tx_rto;
+ u64 tx_rtt_seq:48;
struct timer_list tx_rtotimer;
+
u64 tx_rpseq;
int tx_rpdupack;
unsigned long tx_last_cong;
generated by cgit v1.1 at 2024-10-30 01:49:01 +0000