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-rw-r--r--net/dccp/ccids/ccid2.c171
-rw-r--r--net/dccp/ccids/ccid2.h18
2 files changed, 107 insertions, 82 deletions
diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c
index fa074d442065..22753fd98698 100644
--- a/net/dccp/ccids/ccid2.c
+++ b/net/dccp/ccids/ccid2.c
@@ -110,12 +110,6 @@ 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 *hctx, long val)
-{
- ccid2_pr_debug("change SRTT to %ld\n", val);
- hctx->srtt = val;
-}
-
static void ccid2_start_rto_timer(struct sock *sk);
static void ccid2_hc_tx_rto_expire(unsigned long data)
@@ -123,7 +117,6 @@ static void ccid2_hc_tx_rto_expire(unsigned long data)
struct sock *sk = (struct sock *)data;
struct ccid2_hc_tx_sock *hctx = ccid2_hc_tx_sk(sk);
const bool sender_was_blocked = ccid2_cwnd_network_limited(hctx);
- long s;
bh_lock_sock(sk);
if (sock_owned_by_user(sk)) {
@@ -135,10 +128,8 @@ static void ccid2_hc_tx_rto_expire(unsigned long data)
/* back-off timer */
hctx->rto <<= 1;
-
- s = hctx->rto / HZ;
- if (s > 60)
- hctx->rto = 60 * HZ;
+ if (hctx->rto > DCCP_RTO_MAX)
+ hctx->rto = DCCP_RTO_MAX;
/* adjust pipe, cwnd etc */
hctx->ssthresh = hctx->cwnd / 2;
@@ -279,9 +270,87 @@ 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 *hctx = ccid2_hc_tx_sk(sk);
+ long m = mrtt ? : 1;
+
+ if (hctx->srtt == 0) {
+ /* First measurement m */
+ hctx->srtt = m << 3;
+ hctx->mdev = m << 1;
+
+ hctx->mdev_max = max(TCP_RTO_MIN, hctx->mdev);
+ hctx->rttvar = hctx->mdev_max;
+ hctx->rtt_seq = dccp_sk(sk)->dccps_gss;
+ } else {
+ /* Update scaled SRTT as SRTT += 1/8 * (m - SRTT) */
+ m -= (hctx->srtt >> 3);
+ hctx->srtt += m;
+
+ /* Similarly, update scaled mdev with regard to |m| */
+ if (m < 0) {
+ m = -m;
+ m -= (hctx->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 -= (hctx->mdev >> 2);
+ }
+ hctx->mdev += m;
+
+ if (hctx->mdev > hctx->mdev_max) {
+ hctx->mdev_max = hctx->mdev;
+ if (hctx->mdev_max > hctx->rttvar)
+ hctx->rttvar = hctx->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 as it over-estimates pipe.
+ */
+ if (after48(dccp_sk(sk)->dccps_gar, hctx->rtt_seq)) {
+ if (hctx->mdev_max < hctx->rttvar)
+ hctx->rttvar -= (hctx->rttvar -
+ hctx->mdev_max) >> 2;
+ hctx->rtt_seq = dccp_sk(sk)->dccps_gss;
+ hctx->mdev_max = TCP_RTO_MIN;
+ }
+ }
+
+ /*
+ * Set RTO from SRTT and RTTVAR
+ * Clock granularity is ignored since the minimum error for RTTVAR is
+ * clamped to 50msec (corresponding to HZ=20). This leads to a minimum
+ * RTO of 200msec. This agrees with TCP and RFC 4341, 5.: "Because DCCP
+ * does not retransmit data, DCCP does not require TCP's recommended
+ * minimum timeout of one second".
+ */
+ hctx->rto = (hctx->srtt >> 3) + hctx->rttvar;
+
+ if (hctx->rto > DCCP_RTO_MAX)
+ hctx->rto = DCCP_RTO_MAX;
+}
+
+static void ccid2_new_ack(struct sock *sk, struct ccid2_seq *seqp,
+ unsigned int *maxincr)
{
struct ccid2_hc_tx_sock *hctx = ccid2_hc_tx_sk(sk);
@@ -295,64 +364,15 @@ static inline void ccid2_new_ack(struct sock *sk,
hctx->cwnd += 1;
hctx->packets_acked = 0;
}
-
- /* update RTO */
- if (hctx->srtt == -1 ||
- time_after(jiffies, hctx->lastrtt + hctx->srtt)) {
- unsigned long r = (long)jiffies - (long)seqp->ccid2s_sent;
- int s;
-
- /* first measurement */
- if (hctx->srtt == -1) {
- ccid2_pr_debug("R: %lu Time=%lu seq=%llu\n",
- r, jiffies,
- (unsigned long long)seqp->ccid2s_seq);
- ccid2_change_srtt(hctx, r);
- hctx->rttvar = r >> 1;
- } else {
- /* RTTVAR */
- long tmp = hctx->srtt - r;
- long srtt;
-
- if (tmp < 0)
- tmp *= -1;
-
- tmp >>= 2;
- hctx->rttvar *= 3;
- hctx->rttvar >>= 2;
- hctx->rttvar += tmp;
-
- /* SRTT */
- srtt = hctx->srtt;
- srtt *= 7;
- srtt >>= 3;
- tmp = r >> 3;
- srtt += tmp;
- ccid2_change_srtt(hctx, srtt);
- }
- s = hctx->rttvar << 2;
- /* clock granularity is 1 when based on jiffies */
- if (!s)
- s = 1;
- hctx->rto = hctx->srtt + s;
-
- /* must be at least a second */
- s = hctx->rto / HZ;
- /* DCCP doesn't require this [but I like it cuz my code sux] */
-#if 1
- if (s < 1)
- hctx->rto = HZ;
-#endif
- /* max 60 seconds */
- if (s > 60)
- hctx->rto = HZ * 60;
-
- hctx->lastrtt = jiffies;
-
- ccid2_pr_debug("srtt: %ld rttvar: %ld rto: %ld (HZ=%d) R=%lu\n",
- hctx->srtt, hctx->rttvar,
- hctx->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 - need to be resolved at some time.
+ */
+ ccid2_rtt_estimator(sk, jiffies - seqp->ccid2s_sent);
}
static void ccid2_congestion_event(struct sock *sk, struct ccid2_seq *seqp)
@@ -579,8 +599,7 @@ static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
if (hctx->pipe == 0)
sk_stop_timer(sk, &hctx->rtotimer);
else
- sk_reset_timer(sk, &hctx->rtotimer,
- jiffies + hctx->rto);
+ sk_reset_timer(sk, &hctx->rtotimer, jiffies + hctx->rto);
done:
/* check if incoming Acks allow pending packets to be sent */
if (sender_was_blocked && !ccid2_cwnd_network_limited(hctx))
@@ -613,9 +632,7 @@ static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk)
if (ccid2_hc_tx_alloc_seq(hctx))
return -ENOMEM;
- hctx->rto = 3 * HZ;
- ccid2_change_srtt(hctx, -1);
- hctx->rttvar = -1;
+ hctx->rto = DCCP_TIMEOUT_INIT;
hctx->rpdupack = -1;
hctx->last_cong = jiffies;
setup_timer(&hctx->rtotimer, ccid2_hc_tx_rto_expire, (unsigned long)sk);
diff --git a/net/dccp/ccids/ccid2.h b/net/dccp/ccids/ccid2.h
index d5900dd5d4f4..8b7a2dee2f6d 100644
--- a/net/dccp/ccids/ccid2.h
+++ b/net/dccp/ccids/ccid2.h
@@ -44,7 +44,12 @@ struct ccid2_seq {
*
* @{cwnd,ssthresh,pipe}: as per RFC 4341, section 5
* @packets_acked: Ack counter for deriving cwnd growth (RFC 3465)
- * @lastrtt: time RTT was last measured
+ * @srtt: smoothed RTT estimate, scaled by 2^3
+ * @mdev: smoothed RTT variation, scaled by 2^2
+ * @mdev_max: maximum of @mdev during one flight
+ * @rttvar: moving average/maximum of @mdev_max
+ * @rto: RTO value deriving from SRTT and RTTVAR (RFC 2988)
+ * @rtt_seq: to decay RTTVAR at most once per flight
* @rpseq: last consecutive seqno
* @rpdupack: dupacks since rpseq
* @av_chunks: list of Ack Vectors received on current skb
@@ -58,10 +63,13 @@ struct ccid2_hc_tx_sock {
int seqbufc;
struct ccid2_seq *seqh;
struct ccid2_seq *seqt;
- long rto;
- long srtt;
- long rttvar;
- unsigned long lastrtt;
+ /* RTT measurement: variables/principles are the same as in TCP */
+ u32 srtt,
+ mdev,
+ mdev_max,
+ rttvar,
+ rto;
+ u64 rtt_seq:48;
struct timer_list rtotimer;
u64 rpseq;
int rpdupack;
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