diff options
Diffstat (limited to 'net/ipv4/tcp_input.c')
| -rw-r--r-- | net/ipv4/tcp_input.c | 29 |
1 files changed, 21 insertions, 8 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 9c98dc874825..4ad75b8c4fee 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -2129,10 +2129,25 @@ static bool tcp_pause_early_retransmit(struct sock *sk, int flag) * F.e. after RTO, when all the queue is considered as lost, * lost_out = packets_out and in_flight = retrans_out. * - * Essentially, we have now two algorithms counting + * Essentially, we have now a few algorithms detecting * lost packets. * - * FACK: It is the simplest heuristics. As soon as we decided + * If the receiver supports SACK: + * + * RFC6675/3517: It is the conventional algorithm. A packet is + * considered lost if the number of higher sequence packets + * SACKed is greater than or equal the DUPACK thoreshold + * (reordering). This is implemented in tcp_mark_head_lost and + * tcp_update_scoreboard. + * + * RACK (draft-ietf-tcpm-rack-01): it is a newer algorithm + * (2017-) that checks timing instead of counting DUPACKs. + * Essentially a packet is considered lost if it's not S/ACKed + * after RTT + reordering_window, where both metrics are + * dynamically measured and adjusted. This is implemented in + * tcp_rack_mark_lost. + * + * FACK: it is the simplest heuristics. As soon as we decided * that something is lost, we decide that _all_ not SACKed * packets until the most forward SACK are lost. I.e. * lost_out = fackets_out - sacked_out and left_out = fackets_out. @@ -2141,16 +2156,14 @@ static bool tcp_pause_early_retransmit(struct sock *sk, int flag) * takes place. We use FACK by default until reordering * is suspected on the path to this destination. * - * NewReno: when Recovery is entered, we assume that one segment + * If the receiver does not support SACK: + * + * NewReno (RFC6582): in Recovery we assume that one segment * is lost (classic Reno). While we are in Recovery and * a partial ACK arrives, we assume that one more packet * is lost (NewReno). This heuristics are the same in NewReno * and SACK. * - * Imagine, that's all! Forget about all this shamanism about CWND inflation - * deflation etc. CWND is real congestion window, never inflated, changes - * only according to classic VJ rules. - * * Really tricky (and requiring careful tuning) part of algorithm * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue(). * The first determines the moment _when_ we should reduce CWND and, @@ -2807,7 +2820,7 @@ static void tcp_rack_identify_loss(struct sock *sk, int *ack_flag, struct tcp_sock *tp = tcp_sk(sk); /* Use RACK to detect loss */ - if (sysctl_tcp_recovery & TCP_RACK_LOST_RETRANS) { + if (sysctl_tcp_recovery & TCP_RACK_LOSS_DETECTION) { u32 prior_retrans = tp->retrans_out; tcp_rack_mark_lost(sk, ack_time); |