netdev-dpdk: add support for jumbo frames

Add support for Jumbo Frames to DPDK-enabled port types,
using single-segment-mbufs.

Using this approach, the amount of memory allocated to each mbuf
to store frame data is increased to a value greater than 1518B
(typical Ethernet maximum frame length). The increased space
available in the mbuf means that an entire Jumbo Frame of a specific
size can be carried in a single mbuf, as opposed to partitioning
it across multiple mbuf segments.

The amount of space allocated to each mbuf to hold frame data is
defined dynamically by the user with ovs-vsctl, via the 'mtu_request'
parameter.

Signed-off-by: Mark Kavanagh <mark.b.kavanagh@intel.com>
Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
[diproiettod@vmware.com rebased]
Signed-off-by: Daniele Di Proietto <diproiettod@vmware.com>

1 files changed, 55 insertions, 3 deletions

diff --git a/INSTALL.DPDK-ADVANCED.md b/INSTALL.DPDK-ADVANCED.md
index 11b603aa9..77e202dba 100755
--- a/INSTALL.DPDK-ADVANCED.md
+++ b/INSTALL.DPDK-ADVANCED.md
@@ -1,5 +1,5 @@
 OVS DPDK ADVANCED INSTALL GUIDE
-=================================
+===============================
 
 ## Contents
 
@@ -13,7 +13,8 @@ OVS DPDK ADVANCED INSTALL GUIDE
 8. [Rate Limiting](#rl)
 9. [Flow Control](#fc)
 10. [Pdump](#pdump)
-11. [Vsperf](#vsperf)
+11. [Jumbo Frames](#jumbo)
+12. [Vsperf](#vsperf)
 
 ## <a name="overview"></a> 1. Overview
 
@@ -981,7 +982,58 @@ tcpdump. Issue the following command to view the contents of 'pkts.pcap':
 A performance decrease is expected when using a monitoring application like
 the DPDK pdump app.
 
-## <a name="vsperf"></a> 11. Vsperf
+## <a name="jumbo"></a> 11. Jumbo Frames
+
+By default, DPDK ports are configured with standard Ethernet MTU (1500B). To
+enable Jumbo Frames support for a DPDK port, change the Interface's `mtu_request`
+attribute to a sufficiently large value.
+
+e.g. Add a DPDK Phy port with MTU of 9000:
+
+`ovs-vsctl add-port br0 dpdk0 -- set Interface dpdk0 type=dpdk -- set Interface dpdk0 mtu_request=9000`
+
+e.g. Change the MTU of an existing port to 6200:
+
+`ovs-vsctl set Interface dpdk0 mtu_request=6200`
+
+When Jumbo Frames are enabled, the size of a DPDK port's mbuf segments are
+increased, such that a full Jumbo Frame of a specific size may be accommodated
+within a single mbuf segment.
+
+Jumbo frame support has been validated against 9728B frames (largest frame size
+supported by Fortville NIC), using the DPDK `i40e` driver, but larger frames
+(particularly in use cases involving East-West traffic only), and other DPDK NIC
+drivers may be supported.
+
+### 9.1 vHost Ports and Jumbo Frames
+
+Some additional configuration is needed to take advantage of jumbo frames with
+vhost ports:
+
+    1. `mergeable buffers` must be enabled for vHost ports, as demonstrated in
+        the QEMU command line snippet below:
+
+        ```
+        '-netdev type=vhost-user,id=mynet1,chardev=char0,vhostforce \'
+        '-device virtio-net-pci,mac=00:00:00:00:00:01,netdev=mynet1,mrg_rxbuf=on'
+        ```
+
+    2. Where virtio devices are bound to the Linux kernel driver in a guest
+       environment (i.e. interfaces are not bound to an in-guest DPDK driver),
+       the MTU of those logical network interfaces must also be increased to a
+       sufficiently large value. This avoids segmentation of Jumbo Frames
+       received in the guest. Note that 'MTU' refers to the length of the IP
+       packet only, and not that of the entire frame.
+
+       To calculate the exact MTU of a standard IPv4 frame, subtract the L2
+       header and CRC lengths (i.e. 18B) from the max supported frame size.
+       So, to set the MTU for a 9018B Jumbo Frame:
+
+       ```
+       ifconfig eth1 mtu 9000
+       ```
+
+## <a name="vsperf"></a> 12. Vsperf
 
 Vsperf project goal is to develop vSwitch test framework that can be used to
 validate the suitability of different vSwitch implementations in a Telco deployment