OpenAFS Master Repository branch, master, updated. BP--openafs-stable-1_6_x-1311-ge8c4fc4

Gerrit Code Review
Tue, 21 Jun 2011 18:59:18 -0700 (PDT)

The following commit has been merged in the master branch:
commit 0118fb5387e656e515d78d48497a48f1e04a1152
Author: Simon Wilkinson <>
Date:   Sat Jun 18 11:58:57 2011 +0100

    rx: Add Karn-style backoffs to RX retransmits
    When we retransmit a packet, we may be doing so because the RTT of the
    connection has grown dramatically larger than earlier within the call.
    However, RX doesn't permit all ACKs to retransmitted packets to be
    counted within the RTT calculation.
    So, adopt the same approach as Karn developed for TCP, and as described
    in detail in RFC2988. When a retransmit event occurs, backoff the
    connection RTT by doubling its value, and hold at this doubled value
    until either another retransmit occurs (in which case we back off again,
    up to a predetermined ceiling), or we receive an ACK packet which we
    can use within the RTT calculation, in which case we drop back down to
    the newly measured value.
    This change replaces the per-packet backoff strategy originally
    implemented in RX (which, whilst allowing resent packets more chance of
    arriving, doesn't help with computing a correct RTT).
    Change-Id: I715dc673a0b379733e3be26fa594ea13f492a58f
    Reviewed-by: Derrick Brashear <>
    Reviewed-by: Jeffrey Altman <>
    Tested-by: Jeffrey Altman <>
    Tested-by: BuildBot <>

 src/rx/rx.c |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

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