diff options
| -rw-r--r-- | Documentation/networking/ip-sysctl.txt | 8 | ||||
| -rw-r--r-- | include/linux/tcp.h | 3 | ||||
| -rw-r--r-- | include/net/tcp.h | 7 | ||||
| -rw-r--r-- | net/ipv4/sysctl_net_ipv4.c | 7 | ||||
| -rw-r--r-- | net/ipv4/tcp.c | 1 | ||||
| -rw-r--r-- | net/ipv4/tcp_input.c | 78 | ||||
| -rw-r--r-- | net/ipv4/tcp_minisocks.c | 1 |
7 files changed, 100 insertions, 5 deletions
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt index ebe94f2cab98..502d6a572b4f 100644 --- a/Documentation/networking/ip-sysctl.txt +++ b/Documentation/networking/ip-sysctl.txt @@ -384,6 +384,14 @@ tcp_mem - vector of 3 INTEGERs: min, pressure, max Defaults are calculated at boot time from amount of available memory. +tcp_min_rtt_wlen - INTEGER + The window length of the windowed min filter to track the minimum RTT. + A shorter window lets a flow more quickly pick up new (higher) + minimum RTT when it is moved to a longer path (e.g., due to traffic + engineering). A longer window makes the filter more resistant to RTT + inflations such as transient congestion. The unit is seconds. + Default: 300 + tcp_moderate_rcvbuf - BOOLEAN If set, TCP performs receive buffer auto-tuning, attempting to automatically size the buffer (no greater than tcp_rmem[2]) to diff --git a/include/linux/tcp.h b/include/linux/tcp.h index 86a7edaa6797..90edef5508f9 100644 --- a/include/linux/tcp.h +++ b/include/linux/tcp.h @@ -217,6 +217,9 @@ struct tcp_sock { u32 mdev_max_us; /* maximal mdev for the last rtt period */ u32 rttvar_us; /* smoothed mdev_max */ u32 rtt_seq; /* sequence number to update rttvar */ + struct rtt_meas { + u32 rtt, ts; /* RTT in usec and sampling time in jiffies. */ + } rtt_min[3]; u32 packets_out; /* Packets which are "in flight" */ u32 retrans_out; /* Retransmitted packets out */ diff --git a/include/net/tcp.h b/include/net/tcp.h index eed94fc355c1..4a43152229ea 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -279,6 +279,7 @@ extern int sysctl_tcp_limit_output_bytes; extern int sysctl_tcp_challenge_ack_limit; extern unsigned int sysctl_tcp_notsent_lowat; extern int sysctl_tcp_min_tso_segs; +extern int sysctl_tcp_min_rtt_wlen; extern int sysctl_tcp_autocorking; extern int sysctl_tcp_invalid_ratelimit; extern int sysctl_tcp_pacing_ss_ratio; @@ -671,6 +672,12 @@ static inline bool tcp_ca_dst_locked(const struct dst_entry *dst) return dst_metric_locked(dst, RTAX_CC_ALGO); } +/* Minimum RTT in usec. ~0 means not available. */ +static inline u32 tcp_min_rtt(const struct tcp_sock *tp) +{ + return tp->rtt_min[0].rtt; +} + /* Compute the actual receive window we are currently advertising. * Rcv_nxt can be after the window if our peer push more data * than the offered window. diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c index 894da3a70aff..13ab434c2909 100644 --- a/net/ipv4/sysctl_net_ipv4.c +++ b/net/ipv4/sysctl_net_ipv4.c @@ -577,6 +577,13 @@ static struct ctl_table ipv4_table[] = { .proc_handler = proc_dointvec }, { + .procname = "tcp_min_rtt_wlen", + .data = &sysctl_tcp_min_rtt_wlen, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec + }, + { .procname = "tcp_low_latency", .data = &sysctl_tcp_low_latency, .maxlen = sizeof(int), diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index ac1bdbb50352..0cfa7c0c1e80 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -388,6 +388,7 @@ void tcp_init_sock(struct sock *sk) icsk->icsk_rto = TCP_TIMEOUT_INIT; tp->mdev_us = jiffies_to_usecs(TCP_TIMEOUT_INIT); + tp->rtt_min[0].rtt = ~0U; /* So many TCP implementations out there (incorrectly) count the * initial SYN frame in their delayed-ACK and congestion control diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 62ee71efd1ce..eedb25db3947 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -95,6 +95,7 @@ int sysctl_tcp_stdurg __read_mostly; int sysctl_tcp_rfc1337 __read_mostly; int sysctl_tcp_max_orphans __read_mostly = NR_FILE; int sysctl_tcp_frto __read_mostly = 2; +int sysctl_tcp_min_rtt_wlen __read_mostly = 300; int sysctl_tcp_thin_dupack __read_mostly; @@ -2915,8 +2916,69 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked, tcp_xmit_retransmit_queue(sk); } +/* Kathleen Nichols' algorithm for tracking the minimum value of + * a data stream over some fixed time interval. (E.g., the minimum + * RTT over the past five minutes.) It uses constant space and constant + * time per update yet almost always delivers the same minimum as an + * implementation that has to keep all the data in the window. + * + * The algorithm keeps track of the best, 2nd best & 3rd best min + * values, maintaining an invariant that the measurement time of the + * n'th best >= n-1'th best. It also makes sure that the three values + * are widely separated in the time window since that bounds the worse + * case error when that data is monotonically increasing over the window. + * + * Upon getting a new min, we can forget everything earlier because it + * has no value - the new min is <= everything else in the window by + * definition and it's the most recent. So we restart fresh on every new min + * and overwrites 2nd & 3rd choices. The same property holds for 2nd & 3rd + * best. + */ +static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us) +{ + const u32 now = tcp_time_stamp, wlen = sysctl_tcp_min_rtt_wlen * HZ; + struct rtt_meas *m = tcp_sk(sk)->rtt_min; + struct rtt_meas rttm = { .rtt = (rtt_us ? : 1), .ts = now }; + u32 elapsed; + + /* Check if the new measurement updates the 1st, 2nd, or 3rd choices */ + if (unlikely(rttm.rtt <= m[0].rtt)) + m[0] = m[1] = m[2] = rttm; + else if (rttm.rtt <= m[1].rtt) + m[1] = m[2] = rttm; + else if (rttm.rtt <= m[2].rtt) + m[2] = rttm; + + elapsed = now - m[0].ts; + if (unlikely(elapsed > wlen)) { + /* Passed entire window without a new min so make 2nd choice + * the new min & 3rd choice the new 2nd. So forth and so on. + */ + m[0] = m[1]; + m[1] = m[2]; + m[2] = rttm; + if (now - m[0].ts > wlen) { + m[0] = m[1]; + m[1] = rttm; + if (now - m[0].ts > wlen) + m[0] = rttm; + } + } else if (m[1].ts == m[0].ts && elapsed > wlen / 4) { + /* Passed a quarter of the window without a new min so + * take 2nd choice from the 2nd quarter of the window. + */ + m[2] = m[1] = rttm; + } else if (m[2].ts == m[1].ts && elapsed > wlen / 2) { + /* Passed half the window without a new min so take the 3rd + * choice from the last half of the window. + */ + m[2] = rttm; + } +} + static inline bool tcp_ack_update_rtt(struct sock *sk, const int flag, - long seq_rtt_us, long sack_rtt_us) + long seq_rtt_us, long sack_rtt_us, + long ca_rtt_us) { const struct tcp_sock *tp = tcp_sk(sk); @@ -2936,11 +2998,16 @@ static inline bool tcp_ack_update_rtt(struct sock *sk, const int flag, */ if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr && flag & FLAG_ACKED) - seq_rtt_us = jiffies_to_usecs(tcp_time_stamp - tp->rx_opt.rcv_tsecr); - + seq_rtt_us = ca_rtt_us = jiffies_to_usecs(tcp_time_stamp - + tp->rx_opt.rcv_tsecr); if (seq_rtt_us < 0) return false; + /* ca_rtt_us >= 0 is counting on the invariant that ca_rtt_us is + * always taken together with ACK, SACK, or TS-opts. Any negative + * values will be skipped with the seq_rtt_us < 0 check above. + */ + tcp_update_rtt_min(sk, ca_rtt_us); tcp_rtt_estimator(sk, seq_rtt_us); tcp_set_rto(sk); @@ -2961,7 +3028,7 @@ void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req) rtt_us = skb_mstamp_us_delta(&now, &tcp_rsk(req)->snt_synack); } - tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L); + tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L, rtt_us); } @@ -3175,7 +3242,8 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets, ca_rtt_us = skb_mstamp_us_delta(&now, &sack->last_sackt); } - rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us); + rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us, + ca_rtt_us); if (flag & FLAG_ACKED) { tcp_rearm_rto(sk); diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c index 41828bdc5d32..b875c288daaa 100644 --- a/net/ipv4/tcp_minisocks.c +++ b/net/ipv4/tcp_minisocks.c @@ -470,6 +470,7 @@ struct sock *tcp_create_openreq_child(const struct sock *sk, newtp->srtt_us = 0; newtp->mdev_us = jiffies_to_usecs(TCP_TIMEOUT_INIT); + newtp->rtt_min[0].rtt = ~0U; newicsk->icsk_rto = TCP_TIMEOUT_INIT; newtp->packets_out = 0; |