Message-Id: <200710301948.MAA04351@tardy.cup.hp.com>
Date:	Tue, 30 Oct 2007 12:48:47 -0700 (PDT)
From:	Rick Jones <rick.jones2@...com>
To:	netdev@...r.kernel.org
Subject: [PATCH] remove claim balance_rr won't reorder on many to one

Remove the text which suggests that many balance_rr links feeding into
a single uplink will not experience packet reordering.

More up-to-date tests, with 1G links feeding into a switch with a 10G
uplink, using a 2.6.23-rc8 kernel on the system on which the 1G links
were bonded with balance_rr (mode=0) shows that even a many to one
link configuration will experience packet reordering and the attendant
TCP issues involving spurrious retransmissions and the congestion
window.  This happens even with a single, simple bulk transfer such as
a netperf TCP_STREAM test.  A more complete description of the tests
and results, including tcptrace analysis of packet traces showing the
degree of reordering and such can be found at:

http://marc.info/?l=linux-netdev&m=119101513406349&w=2

Also, note that some switches use the term "trunking" in a context
other than link aggregation.

Signed-off-by:  Rick Jones <rick.jones2@...com>

---
diff -r 35e54d4beaad Documentation/networking/bonding.txt
--- a/Documentation/networking/bonding.txt	Wed Oct 24 05:06:40 2007 +0000
+++ b/Documentation/networking/bonding.txt	Mon Oct 29 03:47:19 2007 -0700
@@ -1696,23 +1696,6 @@ balance-rr: This mode is the only mode t
 	interface's worth of throughput, even after adjusting
 	tcp_reordering.
 
-	Note that this out of order delivery occurs when both the
-	sending and receiving systems are utilizing a multiple
-	interface bond.  Consider a configuration in which a
-	balance-rr bond feeds into a single higher capacity network
-	channel (e.g., multiple 100Mb/sec ethernets feeding a single
-	gigabit ethernet via an etherchannel capable switch).  In this
-	configuration, traffic sent from the multiple 100Mb devices to
-	a destination connected to the gigabit device will not see
-	packets out of order.  However, traffic sent from the gigabit
-	device to the multiple 100Mb devices may or may not see
-	traffic out of order, depending upon the balance policy of the
-	switch.  Many switches do not support any modes that stripe
-	traffic (instead choosing a port based upon IP or MAC level
-	addresses); for those devices, traffic flowing from the
-	gigabit device to the many 100Mb devices will only utilize one
-	interface.
-
 	If you are utilizing protocols other than TCP/IP, UDP for
 	example, and your application can tolerate out of order
 	delivery, then this mode can allow for single stream datagram
@@ -1720,7 +1703,9 @@ balance-rr: This mode is the only mode t
 	to the bond.
 
 	This mode requires the switch to have the appropriate ports
-	configured for "etherchannel" or "trunking."
+	configured for "etherchannel" or "aggregation." N.B. some
+	switches might use the term "trunking" for something other 
+	than link aggregation.
 
 active-backup: There is not much advantage in this network topology to
 	the active-backup mode, as the inactive backup devices are all
-
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