OpenAFS Master Repository branch, master, updated. BP--openafs-stable-1_6_x-1302-gb659449
Gerrit Code Review
Mon, 20 Jun 2011 09:57:03 -0700 (PDT)
The following commit has been merged in the master branch:
Author: Simon Wilkinson <firstname.lastname@example.org>
Date: Fri Jun 17 20:35:59 2011 +0100
rx: Remove incorrect backoff code
The ACK packet handling routine contains code which causes the
RTT to backoff if the selective ACK response indicates that there is
a missing packet. The comment justifies this code as being in line
with Phil Karn's work on TCP.
However, the TCP behaviour is that we backoff when we enter resend. Both
TCP and RX have difficulty computing RTTs for resent packets due to the
ambiguous ACK problem. Whilst RX is slightly better than TCP in this
regard, we can't always tell whether an ACK refers to the original, or
resent packet, so resent packets are unable to contribute to the RTT.
This means that if the RTT ends up too low for the connection, and we
start resending every packet, the RTT will never grow to account for
this, as we never feed it any packet samples.
Karn's solution to this was to backoff (double) the RTT value when we
resend a packet, and then to not drop it back down until we receive an
ACK that we can count. This means that we will always get a new sample
for the connection, and the RTT will grow again.
The original author confirms that the current behaviour in RX is
incorrect, so simply remove it with this patchset.
Reviewed-by: Derrick Brashear <email@example.com>
Tested-by: BuildBot <firstname.lastname@example.org>
src/rx/rx.c | 18 ------------------
src/rx/rx.h | 1 -
2 files changed, 0 insertions(+), 19 deletions(-)
OpenAFS Master Repository