[ovs-dev] [RFC PATCH V4 0/9] netdev-dpdk: support multi-segment mbufs

[Chandran, Sugesh]

Thank you Mark & Michael Qiu for this work.

I had looked at the patch series and have some high level comments as inline.

I would like to test these patch on some of the test scenarios.
so please send a proper patch series once the DPDK17.11 support is added in OVS.

Regards
_Sugesh


> -----Original Message-----
> From: Kavanagh, Mark B
> Sent: Friday, December 8, 2017 12:02 PM
> To: dev at openvswitch.org; qiudayu at chinac.com
> Cc: Stokes, Ian <ian.stokes at intel.com>; Loftus, Ciara <ciara.loftus at intel.com>;
> santosh.shukla at caviumnetworks.com; Chandran, Sugesh
> <sugesh.chandran at intel.com>; Kavanagh, Mark B
> <mark.b.kavanagh at intel.com>
> Subject: [ovs-dev][RFC PATCH V4 0/9] netdev-dpdk: support multi-segment
> mbufs
> 
> Overview
> ========
> This patchset introduces support for multi-segment mbufs to OvS-DPDK.
> Multi-segment mbufs are typically used when the size of an mbuf is insufficient
> to contain the entirety of a packet's data. Instead, the data is split across
> numerous mbufs, each carrying a portion, or 'segment', of the packet data.
> mbufs are chained via their 'next'
> attribute (an mbuf pointer).
> 
> Use Cases
> =========
> i.  Handling oversized (guest-originated) frames, which are marked
>     for hardware accelration/offload (TSO, for example).
> 
>     Packets which originate from a non-DPDK source may be marked for
>     offload; as such, they may be larger than the permitted ingress
>     interface's MTU, and may be stored in an oversized dp-packet. In
>     order to transmit such packets over a DPDK port, their contents
>     must be copied to a DPDK mbuf (via dpdk_do_tx_copy). However, in
>     its current implementation, that function only copies data into
>     a single mbuf; if the space available in the mbuf is exhausted,
>     but not all packet data has been copied, then it is lost.
>     Similarly, when cloning a DPDK mbuf, it must be considered
>     whether that mbuf contains multiple segments. Both issues are
>     resolved within this patchset.
> 
> ii. Handling jumbo frames.
> 
>     While OvS already supports jumbo frames, it does so by increasing
>     mbuf size, such that the entirety of a jumbo frame may be handled
>     in a single mbuf. This is certainly the preferred, and most
>     performant approach (and remains the default). However, it places
>     high demands on system memory; multi-segment mbufs may be
>     prefereable for systems which are memory-constrained.
> 
> Enabling multi-segment mbufs
> ============================
> Multi-segment and single-segment mbufs are mutually exclusive, and the user
> must decide on which approach to adopt on init. The introduction of a new
> OVSDB field, 'dpdk-multi-seg-mbufs', facilitates this.
> 
> This is a global boolean value, which determines how jumbo frames are
> represented across all DPDK ports. In the absence of a user-supplied value,
> 'dpdk-multi-seg-mbufs' defaults to false, i.e. multi-segment mbufs must be
> explicitly enabled / single-segment mbufs remain the default.
> 
> Setting the field is identical to setting existing DPDK-specific OVSDB
> fields:
> 
>     ovs-vsctl set Open_vSwitch . other_config:dpdk-init=true
>     ovs-vsctl set Open_vSwitch . other_config:dpdk-lcore-mask=0x10
>     ovs-vsctl set Open_vSwitch . other_config:dpdk-socket-mem=4096,0
> ==> ovs-vsctl set Open_vSwitch . other_config:dpdk-multi-seg-mbufs=true
> 
> 
> Notes
> =====
> This patchset was generated and built against:
> - Current HEAD of OvS master[1] + DPDK v17.11 support patchset[2]
> - DPDK v17.11
> 
> [1] 159cc1f ("datapath-windows: Correct endianness for deleting zone.") [2]
> https://mail.openvswitch.org/pipermail/ovs-dev/2017-December/341786.html
> 
> ---
> 
> v4: - restructure patchset
>     - account for 128B ARM cacheline when sizing mbufs
> 
> Mark Kavanagh (5):
>   netdev-dpdk: fix mbuf sizing
>   dp-packet: fix reset_packet for multi-seg mbufs
>   dp-packet: fix put_uninit for multi-seg mbufs
>   dp-packet: init specific mbuf fields to 0
>   netdev-dpdk: support multi-segment jumbo frames
> 
> Michael Qiu (4):
>   dp-packet: Fix data_len issue with multi-seg mbufs
>   dp-packet: copy mbuf info for packet copy
>   dp-packet: copy data from multi-seg. DPDK mbuf
>   netdev-dpdk: copy large packet to multi-seg. mbufs
> 
>  NEWS                 |   1 +
>  lib/dp-packet.c      |  51 ++++++++++++++++-
>  lib/dp-packet.h      |  26 ++++-----
>  lib/dpdk.c           |   7 +++
>  lib/netdev-dpdk.c    | 156 ++++++++++++++++++++++++++++++++++++++++++---
> ------
>  lib/netdev-dpdk.h    |   1 +
>  vswitchd/vswitch.xml |  20 +++++++
>  7 files changed, 220 insertions(+), 42 deletions(-)
> 
> --
> 1.9.3