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Commit 66205121 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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tcp: grow window for OOO packets only for SACK flows



Back in 2013, we made a change that broke fast retransmit
for non SACK flows.

Indeed, for these flows, a sender needs to receive three duplicate
ACK before starting fast retransmit. Sending ACK with different
receive window do not count.

Even if enabling SACK is strongly recommended these days,
there still are some cases where it has to be disabled.

Not increasing the window seems better than having to
rely on RTO.

After the fix, following packetdrill test gives :

// Initialize connection
    0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
   +0 bind(3, ..., ...) = 0
   +0 listen(3, 1) = 0

   +0 < S 0:0(0) win 32792 <mss 1000,nop,wscale 7>
   +0 > S. 0:0(0) ack 1 <mss 1460,nop,wscale 8>
   +0 < . 1:1(0) ack 1 win 514

   +0 accept(3, ..., ...) = 4

   +0 < . 1:1001(1000) ack 1 win 514
// Quick ack
   +0 > . 1:1(0) ack 1001 win 264

   +0 < . 2001:3001(1000) ack 1 win 514
// DUPACK : Normally we should not change the window
   +0 > . 1:1(0) ack 1001 win 264

   +0 < . 3001:4001(1000) ack 1 win 514
// DUPACK : Normally we should not change the window
   +0 > . 1:1(0) ack 1001 win 264

   +0 < . 4001:5001(1000) ack 1 win 514
// DUPACK : Normally we should not change the window
    +0 > . 1:1(0) ack 1001 win 264

   +0 < . 1001:2001(1000) ack 1 win 514
// Hole is repaired.
   +0 > . 1:1(0) ack 5001 win 272

Fixes: 4e4f1fc2 ("tcp: properly increase rcv_ssthresh for ofo packets")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reported-by: default avatarVenkat Venkatsubra <venkat.x.venkatsubra@oracle.com>
Acked-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent b8ad540d
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