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08 September 2024, 02:26:05 UTC
Revision da34ac7626b571d262f92b93f11eb32dd58d9c4e authored by Yuchung Cheng on 18 May 2015, 19:31:44 UTC, committed by David S. Miller on 19 May 2015, 20:36:57 UTC 
tcp: only undo on partial ACKs in CA_Loss
 
Undo based on TCP timestamps should only happen on ACKs that advance
SND_UNA, according to the Eifel algorithm in RFC 3522:

Section 3.2:

  (4) If the value of the Timestamp Echo Reply field of the
      acceptable ACK's Timestamps option is smaller than the
      value of RetransmitTS, then proceed to step (5),

Section Terminology:
   We use the term 'acceptable ACK' as defined in [RFC793].  That is an
   ACK that acknowledges previously unacknowledged data.

This is because upon receiving an out-of-order packet, the receiver
returns the last timestamp that advances RCV_NXT, not the current
timestamp of the packet in the DUPACK. Without checking the flag,
the DUPACK will cause tcp_packet_delayed() to return true and
tcp_try_undo_loss() will revert cwnd reduction.

Note that we check the condition in CA_Recovery already by only
calling tcp_try_undo_partial() if FLAG_SND_UNA_ADVANCED is set or
tcp_try_undo_recovery() if snd_una crosses high_seq.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
1 parent 33b4b01
History
Tip revision: da34ac7626b571d262f92b93f11eb32dd58d9c4e authored by Yuchung Cheng on 18 May 2015, 19:31:44 UTC
tcp: only undo on partial ACKs in CA_Loss
Tip revision: da34ac7
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