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-rw-r--r--kernel/net/ipv4/tcp_recovery.c109
1 files changed, 109 insertions, 0 deletions
diff --git a/kernel/net/ipv4/tcp_recovery.c b/kernel/net/ipv4/tcp_recovery.c
new file mode 100644
index 000000000..5353085fd
--- /dev/null
+++ b/kernel/net/ipv4/tcp_recovery.c
@@ -0,0 +1,109 @@
+#include <linux/tcp.h>
+#include <net/tcp.h>
+
+int sysctl_tcp_recovery __read_mostly = TCP_RACK_LOST_RETRANS;
+
+/* Marks a packet lost, if some packet sent later has been (s)acked.
+ * The underlying idea is similar to the traditional dupthresh and FACK
+ * but they look at different metrics:
+ *
+ * dupthresh: 3 OOO packets delivered (packet count)
+ * FACK: sequence delta to highest sacked sequence (sequence space)
+ * RACK: sent time delta to the latest delivered packet (time domain)
+ *
+ * The advantage of RACK is it applies to both original and retransmitted
+ * packet and therefore is robust against tail losses. Another advantage
+ * is being more resilient to reordering by simply allowing some
+ * "settling delay", instead of tweaking the dupthresh.
+ *
+ * The current version is only used after recovery starts but can be
+ * easily extended to detect the first loss.
+ */
+int tcp_rack_mark_lost(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *skb;
+ u32 reo_wnd, prior_retrans = tp->retrans_out;
+
+ if (inet_csk(sk)->icsk_ca_state < TCP_CA_Recovery || !tp->rack.advanced)
+ return 0;
+
+ /* Reset the advanced flag to avoid unnecessary queue scanning */
+ tp->rack.advanced = 0;
+
+ /* To be more reordering resilient, allow min_rtt/4 settling delay
+ * (lower-bounded to 1000uS). We use min_rtt instead of the smoothed
+ * RTT because reordering is often a path property and less related
+ * to queuing or delayed ACKs.
+ *
+ * TODO: measure and adapt to the observed reordering delay, and
+ * use a timer to retransmit like the delayed early retransmit.
+ */
+ reo_wnd = 1000;
+ if (tp->rack.reord && tcp_min_rtt(tp) != ~0U)
+ reo_wnd = max(tcp_min_rtt(tp) >> 2, reo_wnd);
+
+ tcp_for_write_queue(skb, sk) {
+ struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
+
+ if (skb == tcp_send_head(sk))
+ break;
+
+ /* Skip ones already (s)acked */
+ if (!after(scb->end_seq, tp->snd_una) ||
+ scb->sacked & TCPCB_SACKED_ACKED)
+ continue;
+
+ if (skb_mstamp_after(&tp->rack.mstamp, &skb->skb_mstamp)) {
+
+ if (skb_mstamp_us_delta(&tp->rack.mstamp,
+ &skb->skb_mstamp) <= reo_wnd)
+ continue;
+
+ /* skb is lost if packet sent later is sacked */
+ tcp_skb_mark_lost_uncond_verify(tp, skb);
+ if (scb->sacked & TCPCB_SACKED_RETRANS) {
+ scb->sacked &= ~TCPCB_SACKED_RETRANS;
+ tp->retrans_out -= tcp_skb_pcount(skb);
+ NET_INC_STATS_BH(sock_net(sk),
+ LINUX_MIB_TCPLOSTRETRANSMIT);
+ }
+ } else if (!(scb->sacked & TCPCB_RETRANS)) {
+ /* Original data are sent sequentially so stop early
+ * b/c the rest are all sent after rack_sent
+ */
+ break;
+ }
+ }
+ return prior_retrans - tp->retrans_out;
+}
+
+/* Record the most recently (re)sent time among the (s)acked packets */
+void tcp_rack_advance(struct tcp_sock *tp,
+ const struct skb_mstamp *xmit_time, u8 sacked)
+{
+ if (tp->rack.mstamp.v64 &&
+ !skb_mstamp_after(xmit_time, &tp->rack.mstamp))
+ return;
+
+ if (sacked & TCPCB_RETRANS) {
+ struct skb_mstamp now;
+
+ /* If the sacked packet was retransmitted, it's ambiguous
+ * whether the retransmission or the original (or the prior
+ * retransmission) was sacked.
+ *
+ * If the original is lost, there is no ambiguity. Otherwise
+ * we assume the original can be delayed up to aRTT + min_rtt.
+ * the aRTT term is bounded by the fast recovery or timeout,
+ * so it's at least one RTT (i.e., retransmission is at least
+ * an RTT later).
+ */
+ skb_mstamp_get(&now);
+ if (skb_mstamp_us_delta(&now, xmit_time) < tcp_min_rtt(tp))
+ return;
+ }
+
+ tp->rack.mstamp = *xmit_time;
+ tp->rack.advanced = 1;
+}