Commit 3a91d29f authored Oct 22, 2017 by Koichiro Den Committed by David S. Miller Oct 23, 2017

tcp: do tcp_mstamp_refresh before retransmits on TSQ handler



When retransmission on TSQ handler was introduced in the commit
f9616c35 ("tcp: implement TSQ for retransmits"), the retransmitted
skbs' timestamps were updated on the actual transmission. In the later
commit 385e2070 ("tcp: use tp->tcp_mstamp in output path"), it stops
being done so. In the commit, the comment says "We try to refresh
tp->tcp_mstamp only when necessary", and at present tcp_tsq_handler and
tcp_v4_mtu_reduced applies to this. About the latter, it's okay since
it's rare enough.

About the former, even though possible retransmissions on the tasklet
comes just after the destructor run in NET_RX softirq handling, the time
between them could be nonnegligibly large to the extent that
tcp_rack_advance or rto rearming be affected if other (remaining) RX,
BLOCK and (preceding) TASKLET sofirq handlings are unexpectedly heavy.

So in the same way as tcp_write_timer_handler does, doing tcp_mstamp_refresh
ensures the accuracy of algorithms relying on it.

Fixes: 385e2070 ("tcp: use tp->tcp_mstamp in output path")
Signed-off-by: Koichiro Den <den@klaipeden.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent b5ac3beb

net/ipv4/tcp_output.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -739,8 +739,10 @@ static void tcp_tsq_handler(struct sock *sk)
		struct tcp_sock *tp = tcp_sk(sk);

		if (tp->lost_out > tp->retrans_out &&
		tp->snd_cwnd > tcp_packets_in_flight(tp))
		tp->snd_cwnd > tcp_packets_in_flight(tp)) {
		tcp_mstamp_refresh(tp);
		tcp_xmit_retransmit_queue(sk);
		}

		tcp_write_xmit(sk, tcp_current_mss(sk), tp->nonagle,
		0, GFP_ATOMIC);

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