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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.

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>
This commit is contained in:
Yuchung Cheng 2019-01-16 15:05:30 -08:00 committed by David S. Miller
parent 7f12422c48
commit 7ae189759c
2 changed files with 7 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
net/ipv4/tcp_output.c
View File

@ -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. */
if (!tp->retrans_stamp)
tp->retrans_stamp = tcp_skb_timestamp(skb);
}
/* 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);

23
net/ipv4/tcp_timer.c
View File

@ -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);