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;