tcp: always set retrans_stamp on recovery (7ae18975) · Commits · 戴 / test

Previously TCP socket's retrans_stamp is not set if the retransmission has failed to send. As a result if a socket is experiencing local issues to retransmit packets, determining when to abort a socket is complicated w/o knowning the starting time of the recovery since retrans_stamp may remain zero. This complication causes sub-optimal behavior that TCP may use the latest, instead of the first, retransmission time to compute the elapsed time of a stalling connection due to local issues. Then TCP may disrecard TCP retries settings and keep retrying until it finally succeed: not a good idea when the local host is already strained. The simple fix is to always timestamp the start of a recovery. It's worth noting that retrans_stamp is also used to compare echo timestamp values to detect spurious recovery. This patch does not break that because retrans_stamp is still later than when the original packet was sent. Signed-off-by:

Yuchung Cheng <ycheng@google.com> Signed-off-by:

Eric Dumazet <edumazet@google.com> Reviewed-by:

Neal Cardwell <ncardwell@google.com> Reviewed-by:

Soheil Hassas Yeganeh <soheil@google.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/ipv4/tcp_output.c

+4 −5

Original line number	Diff line number	Diff line
		@@ -2963,13 +2963,12 @@ int tcp_retransmit_skb(struct sock sk, struct sk_buff skb, int segs)
		#endif
		TCP_SKB_CB(skb)->sacked \|= TCPCB_RETRANS;
		tp->retrans_out += tcp_skb_pcount(skb);
		}

		/* Save stamp of the first retransmit. */
		/* Save stamp of the first (attempted) retransmit. */
		if (!tp->retrans_stamp)
		tp->retrans_stamp = tcp_skb_timestamp(skb);

		}

		if (tp->undo_retrans < 0)
		tp->undo_retrans = 0;
		tp->undo_retrans += tcp_skb_pcount(skb);

net/ipv4/tcp_timer.c

+3 −20

Original line number	Diff line number	Diff line
		@@ -22,28 +22,14 @@
		#include <linux/gfp.h>
		#include <net/tcp.h>

		static u32 tcp_retransmit_stamp(const struct sock *sk)
		{
		u32 start_ts = tcp_sk(sk)->retrans_stamp;

		if (unlikely(!start_ts)) {
		struct sk_buff *head = tcp_rtx_queue_head(sk);

		if (!head)
		return 0;
		start_ts = tcp_skb_timestamp(head);
		}
		return start_ts;
		}

		static u32 tcp_clamp_rto_to_user_timeout(const struct sock *sk)
		{
		struct inet_connection_sock *icsk = inet_csk(sk);
		u32 elapsed, start_ts;
		s32 remaining;

		start_ts = tcp_retransmit_stamp(sk);
		if (!icsk->icsk_user_timeout \|\| !start_ts)
		start_ts = tcp_sk(sk)->retrans_stamp;
		if (!icsk->icsk_user_timeout)
		return icsk->icsk_rto;
		elapsed = tcp_time_stamp(tcp_sk(sk)) - start_ts;
		remaining = icsk->icsk_user_timeout - elapsed;
		@@ -197,10 +183,7 @@ static bool retransmits_timed_out(struct sock *sk,
		if (!inet_csk(sk)->icsk_retransmits)
		return false;

		start_ts = tcp_retransmit_stamp(sk);
		if (!start_ts)
		return false;

		start_ts = tcp_sk(sk)->retrans_stamp;
		if (likely(timeout == 0)) {
		linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base);

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