bonding: Add tlb_dynamic_lb parameter for tlb mode

The aggresive load balancing causes packet re-ordering as active
flows are moved from a slave to another within the group. Sometime
this aggresive lb is not necessary if the preference is for less
re-ordering. This parameter if used with value "0" disables
this dynamic flow shuffling minimizing packet re-ordering. Of course
the side effect is that it has to live with the static load balancing
that the hashing distribution provides. This impact is less severe if
the correct xmit-hashing-policy is used for the tlb setup.

The default value of the parameter is set to "1" mimicing the earlier
behavior.

Ran the netperf test with 200 stream for 1 min between two hosts with
4x1G trunk (xmit-lb mode with xmit-policy L3+4) before and after these
changes. Following was the command used for those 200 instances -

    netperf -t TCP_RR -l 60 -s 5 -H <host> -- -r81920,81920

Transactions per second:
    Before change: 1,367.11
    After  change: 1,470.65

Change-Id: Ie3f75c77282cf602e83a6e833c6eb164e72a0990
Signed-off-by: Mahesh Bandewar <maheshb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 35 insertions, 7 deletions

diff --git a/Documentation/networking/bonding.txt b/Documentation/networking/bonding.txt
index a97c567f24e8..9c723ecd0025 100644
--- a/Documentation/networking/bonding.txt
+++ b/Documentation/networking/bonding.txt
@@ -585,13 +585,19 @@ mode
         balance-tlb or 5
 
                 Adaptive transmit load balancing: channel bonding that
-                does not require any special switch support.  The
-                outgoing traffic is distributed according to the
-                current load (computed relative to the speed) on each
-                slave.  Incoming traffic is received by the current
-                slave.  If the receiving slave fails, another slave
-                takes over the MAC address of the failed receiving
-                slave.
+                does not require any special switch support.
+
+                In tlb_dynamic_lb=1 mode; the outgoing traffic is
+                distributed according to the current load (computed
+                relative to the speed) on each slave.
+
+                In tlb_dynamic_lb=0 mode; the load balancing based on
+                current load is disabled and the load is distributed
+                only using the hash distribution.
+
+                Incoming traffic is received by the current slave.
+                If the receiving slave fails, another slave takes over
+                the MAC address of the failed receiving slave.
 
                 Prerequisite:
 
@@ -736,6 +742,28 @@ primary_reselect
 
         This option was added for bonding version 3.6.0.
 
+tlb_dynamic_lb
+
+        Specifies if dynamic shuffling of flows is enabled in tlb
+        mode. The value has no effect on any other modes.
+
+        The default behavior of tlb mode is to shuffle active flows across
+        slaves based on the load in that interval. This gives nice lb
+        characteristics but can cause packet reordering. If re-ordering is
+        a concern use this variable to disable flow shuffling and rely on
+        load balancing provided solely by the hash distribution.
+        xmit-hash-policy can be used to select the appropriate hashing for
+        the setup.
+
+        The sysfs entry can be used to change the setting per bond device
+        and the initial value is derived from the module parameter. The
+        sysfs entry is allowed to be changed only if the bond device is
+        down.
+
+        The default value is "1" that enables flow shuffling while value "0"
+        disables it. This option was added in bonding driver 3.7.1
+
+
 updelay
 
         Specifies the time, in milliseconds, to wait before enabling a