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>
parent
33b4b015
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