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Commit 2aa81b16 authored by Yuchung Cheng's avatar Yuchung Cheng Committed by Kaustubh Pandey
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tcp: always set retrans_stamp on recovery 



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.

Change-Id: I8d13ee5aee5ba84d3c42fb34fbb46da942a4b7d7
Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reviewed-by: default avatarNeal Cardwell <ncardwell@google.com>
Reviewed-by: default avatarSoheil Hassas Yeganeh <soheil@google.com>
Git-Commit: 7ae189759cc48cf8b54beebff566e9fd2d4e7d7c
Git-repo: https://android.googlesource.com/kernel/common/


Signed-off-by: default avatarKaustubh Pandey <kapandey@codeaurora.org>
parent 57d532a0

net/ipv4/tcp_output.c

+4 −5
Original line number Diff line number Diff line
@@ -2957,13 +2957,12 @@ 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;
@@ -230,10 +216,7 @@ 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);