path: root/Documentation/networking
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authorEric Dumazet <>2014-10-27 21:45:24 -0700
committerDavid S. Miller <>2014-10-29 15:05:15 -0400
commitdca145ffaa8d39ea1904491ac81b92b7049372c0 (patch)
treeebe67ece694b9e54281047a6037b7d5776f9f56b /Documentation/networking
parent7aef06db0f91c7b48305d07b62edf43179adb28c (diff)
tcp: allow for bigger reordering level
While testing upcoming Yaogong patch (converting out of order queue into an RB tree), I hit the max reordering level of linux TCP stack. Reordering level was limited to 127 for no good reason, and some network setups [1] can easily reach this limit and get limited throughput. Allow a new max limit of 300, and add a sysctl to allow admins to even allow bigger (or lower) values if needed. [1] Aggregation of links, per packet load balancing, fabrics not doing deep packet inspections, alternative TCP congestion modules... Signed-off-by: Eric Dumazet <> Cc: Yaogong Wang <> Signed-off-by: David S. Miller <>
Diffstat (limited to 'Documentation/networking')
2 files changed, 11 insertions, 6 deletions
diff --git a/Documentation/networking/bonding.txt b/Documentation/networking/bonding.txt
index eeb5b2e97bed..83bf4986baea 100644
--- a/Documentation/networking/bonding.txt
+++ b/Documentation/networking/bonding.txt
@@ -2230,11 +2230,8 @@ balance-rr: This mode is the only mode that will permit a single
It is possible to adjust TCP/IP's congestion limits by
altering the net.ipv4.tcp_reordering sysctl parameter. The
- usual default value is 3, and the maximum useful value is 127.
- For a four interface balance-rr bond, expect that a single
- TCP/IP stream will utilize no more than approximately 2.3
- interface's worth of throughput, even after adjusting
- tcp_reordering.
+ usual default value is 3. But keep in mind TCP stack is able
+ to automatically increase this when it detects reorders.
Note that the fraction of packets that will be delivered out of
order is highly variable, and is unlikely to be zero. The level
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 0307e2875f21..9028b879a97b 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -376,9 +376,17 @@ tcp_orphan_retries - INTEGER
may consume significant resources. Cf. tcp_max_orphans.
tcp_reordering - INTEGER
- Maximal reordering of packets in a TCP stream.
+ Initial reordering level of packets in a TCP stream.
+ TCP stack can then dynamically adjust flow reordering level
+ between this initial value and tcp_max_reordering
Default: 3
+tcp_max_reordering - INTEGER
+ Maximal reordering level of packets in a TCP stream.
+ 300 is a fairly conservative value, but you might increase it
+ if paths are using per packet load balancing (like bonding rr mode)
+ Default: 300
tcp_retrans_collapse - BOOLEAN
Bug-to-bug compatibility with some broken printers.
On retransmit try to send bigger packets to work around bugs in