[ovs-dev] [RFC v2] docs: Describe output packet batching in DPDK guide.

[Ilya Maximets]

Added information about output packet batching and a way to
configure 'tx-flush-interval'.

Signed-off-by: Ilya Maximets <i.maximets at samsung.com>
---

Version 2:
	* Some grammar/wording corrections. (Eelco Chaudron)

 Documentation/intro/install/dpdk.rst | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/Documentation/intro/install/dpdk.rst b/Documentation/intro/install/dpdk.rst
index 3fecb5c..5485dbc 100644
--- a/Documentation/intro/install/dpdk.rst
+++ b/Documentation/intro/install/dpdk.rst
@@ -568,6 +568,30 @@ not needed i.e. jumbo frames are not needed, it can be forced off by adding
 chains of descriptors it will make more individual virtio descriptors available
 for rx to the guest using dpdkvhost ports and this can improve performance.
 
+Output Packet Batching
+~~~~~~~~~~~~~~~~~~~~~~
+
+To get advantages of the batched send functions OVS collects packets in
+intermediate queues before sending. This allows using a single send for
+packets matched by different flows but having the same output action.
+Furthermore, OVS is able to collect packets for some reasonable amount of time
+before batch sending them which might help when input batches are small.
+
+``tx-flush-interval`` config could be used to specify the time in microseconds
+that a packet can wait in an output queue for sending (default is ``0``)::
+
+    $ ovs-vsctl set Open_vSwitch . other_config:tx-flush-interval=50
+
+Lower values decrease latency while higher values may be useful to achieve
+higher performance. For example, increasing of ``tx-flush-interval`` can be
+used to decrease the number of interrupts for interrupt based guest drivers.
+This may significantly affect the performance. Zero value means immediate
+send at the end of processing a single input batch.
+
+Average number of packets per output batch could be checked in PMD stats::
+
+    $ ovs-appctl dpif-netdev/pmd-stats-show
+
 Limitations
 ------------
 
-- 
2.7.4