Signed-off-by: Mark Kavanagh <[email protected]>
---
INSTALL.DPDK.md | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 59 insertions(+)
diff --git a/INSTALL.DPDK.md b/INSTALL.DPDK.md
index 722fb9e..4ca98cb 100644
--- a/INSTALL.DPDK.md
+++ b/INSTALL.DPDK.md
@@ -878,6 +878,60 @@ by adding the following string:
to <interface> sections of all network devices used by DPDK. Parameter 'N'
determines how many queues can be used by the guest.
+Jumbo Frames
+------------
+
+Support for Jumbo Frames may be enabled at run-time for DPDK-type ports.
+
+To avail of Jumbo Frame support, add the 'mtu_request' option to the ovs-vsctl
+'add-port' command-line, along with the required MTU for the port.
+e.g.
+
+ ```
+ ovs-vsctl add-port br0 dpdk0 -- set Interface dpdk0 type=dpdk
options:mtu_request=9000
+ ```
+
+When Jumbo Frames are enabled, the size of a DPDK port's mbuf segments are
+increased, such that a full Jumbo Frame may be accommodated inside a single
+mbuf segment. Once set, the MTU for a DPDK port is immutable.
+
+Note that from an OVSDB perspective, the `mtu_request` option for a specific
+port may be disregarded once initially set, as subsequent modifications to this
+field are disregarded by the DPDK port. As with non-DPDK ports, the MTU of DPDK
+ports is reported by the `Interface` table's `mtu` field.
+
+Jumbo frame support has been validated against 13312B frames, using the
+DPDK `igb_uio` driver, but larger frames and other DPDK NIC drivers may
+theoretically be supported. Supported port types excludes vHost-Cuse ports, as
+that feature is pending deprecation.
+
+vHost Ports and Jumbo Frames
+----------------------------
+Jumbo frame support is available for DPDK vHost-User ports only. Some
additional
+configuration is needed to take advantage of this feature:
+
+ 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. This
+ avoids segmentation of Jumbo Frames in the guest. Note that 'MTU' refers
+ to the length of the IP packet only, and not that of the entire frame.
+
+ e.g. 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 13312B Jumbo Frame:
+
+ ```
+ ifconfig eth1 mtu 13294
+ ```
+
Restrictions:
-------------
@@ -921,6 +975,11 @@ Restrictions:
the next release of DPDK (which includes the above patch) is available and
integrated into OVS.
+ Jumbo Frames:
+ - `virtio-pmd`: DPDK apps in the guest do not exit gracefully. This is a DPDK
+ issue that is currently being investigated.
+ - vHost-Cuse: Jumbo Frame support is not available for vHost Cuse ports.
+
Bug Reporting:
--------------
--
1.9.3
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