[ovs-dev] [PATCH v3 0/2] vHost Dequeue Zero Copy

Ciara Loftus ciara.loftus at intel.com
Mon Oct 16 15:13:32 UTC 2017

This patch enables optional dequeue zero copy for vHost ports.
This gives a performance increase for some use cases. I'm using
the cover letter to report my results.

vhost (vm1) -> vhost (vm2)
Using testpmd to source (txonly) in vm1 and sink (rxonly) in vm2.
4C1Q 64B packets: 5.05Mpps -> 5.52Mpps = 9.2% improvement
256B:    4.69 vs 5.42 Mpps (+~16%)
512B:    4.04 vs 4.90 Mpps (+~21%)
1518B:    2.51 vs 3.05 Mpps (+~22%)

vhost (virtio_user backend 1) -> vhost (virtio_user backend 2)
Using 2 instances of testpmd, each with a virtio_user backend
connected to one of the two vhost ports created in OVS.
2C1Q 1518B packets: 2.59Mpps -> 3.09Mpps = 19.3% improvement

vhost -> phy
Using testpmd to source (txonly) and sink in the NIC
1C1Q 64B packets: 6.81Mpps -> 7.76Mpps = 13.9% improvement

phy -> vhost -> phy
No improvement measured

This patch is dependent on the series below which fixes issues with
mempool management:

* Documentation updates:
** Style fixes
** Elaborate on expected logs
** Describe how to disable the feature
** Describe NIC descriptors limitation in more detail

v2 changes:
* Mention feature is disabled by default in the documentation
* Add PHY-VM-PHY with vHost dequeue zero copy documentation guide
* Line wrap link to DPDK documentation
* Rename zc_enabled to dq_zc_enabled for future-proofing
* Mention feature is available for both vHost port types in the docs
* In practise, rebooting the VM doesn't always enable the feature if
enabled post-boot, so update the documentation to suggest a shutdown
rather than a reboot. The reason why this doesn't work is probably
because the total downtime during reboot isn't enough to allow a vhost
device unregister & re-register with the new feature, so when the VM
starts again it doesn't pick up the new device as it hasn't been
re-registered in time.

Ciara Loftus (2):
  netdev-dpdk: Helper function for vHost device setup
  netdev-dpdk: Enable optional dequeue zero copy for vHost User

 Documentation/howto/dpdk.rst             |  33 +++++
 Documentation/topics/dpdk/vhost-user.rst |  58 +++++++++
 NEWS                                     |   3 +
 lib/netdev-dpdk.c                        | 202 +++++++++++++++++++++----------
 vswitchd/vswitch.xml                     |  11 ++
 5 files changed, 245 insertions(+), 62 deletions(-)


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