[v5,00/11] implement packed virtqueues
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Message ID 20180906181947.20646-1-jfreimann@redhat.com
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  • implement packed virtqueues
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Jens Freimann Sept. 6, 2018, 6:19 p.m. UTC
This is a basic implementation of packed virtqueues as specified in the
Virtio 1.1 draft. A compiled version of the current draft is available
at https://github.com/oasis-tcs/virtio-docs.git (or as .pdf at

It does not implement yet indirect descriptors and checksum offloading.

A packed virtqueue is different from a split virtqueue in that it
consists of only a single descriptor ring that replaces available and
used ring, index and descriptor buffer.

Each descriptor is readable and writable and has a flags field. These flags
will mark if a descriptor is available or used.  To detect new available descriptors
even after the ring has wrapped, device and driver each have a
single-bit wrap counter that is flipped from 0 to 1 and vice versa every time
the last descriptor in the ring is used/made available.

The idea behind this is to 1. improve performance by avoiding cache misses
and 2. be easier for devices to implement.

Regarding performance: with these patches I get 21.13 Mpps on my system
as compared to 18.8 Mpps with the virtio 1.0 code. Packet size was 64
bytes, 0.05% acceptable loss.  Test setup is described as in

Packet generator:
Intel(R) Xeon(R) CPU E5-2665 0 @ 2.40GHz
Intel X710 NIC
RHEL 7.4

Device under test:
Intel(R) Xeon(R) CPU E5-2667 v4 @ 3.20GHz
Intel X710 NIC
RHEL 7.4

VM on DuT: RHEL7.4

I plan to do more performance test with bigger frame sizes.

changes from v4->v5:
* fix VIRTQUEUE_DUMP macro
* fix wrap counter logic in transmit and receive functions  

changes from v3->v4:
* added helpers to increment index and set available/used flags
* driver keeps track of number of descriptors used
* change logic in set_rxtx_funcs()
* add patch for ctrl virtqueue with support for packed virtqueues
* rename virtio-1.1.h to virtio-packed.h
* fix wrong sizeof() in "vhost: vring address setup for packed queues"
* fix coding style of function definition in "net/virtio: add packed
  virtqueue helpers"
* fix padding in vring_size()
* move patches to enable packed virtqueues end of series
* v4 has two open problems: I'm sending it out anyway for feedback/help:
 * when VIRTIO_NET_F_MRG_RXBUF enabled only 128 packets are send in
   guest, i.e. when ring is full for the first time. I suspect a bug in
   setting the avail/used flags

changes from v2->v3:
* implement event suppression
* add code do dump packed virtqueues
* don't use assert in vhost code
* rename virtio-user parameter to packed-vq
* support rxvf flush

changes from v1->v2:
* don't use VIRTQ_DESC_F_NEXT in used descriptors (Jason)
* no rte_panice() in guest triggerable code (Maxime)
* use unlikely when checking for vq (Maxime)
* rename everything from _1_1 to _packed  (Yuanhan)
* add two more patches to implement mergeable receive buffers

Jens Freimann (10):
  net/virtio: vring init for packed queues
  net/virtio: add virtio 1.1 defines
  net/virtio: add packed virtqueue helpers
  net/virtio: flush packed receive virtqueues
  net/virtio: dump packed virtqueue data
  net/virtio: implement transmit path for packed queues
  net/virtio: implement receive path for packed queues
  net/virtio: disable ctrl virtqueue for packed rings
  net/virtio: add support for mergeable buffers with packed virtqueues
  net/virtio: add support for event suppression

Yuanhan Liu (1):
  net/virtio-user: add option to use packed queues

 drivers/net/virtio/virtio_ethdev.c            |  50 ++-
 drivers/net/virtio/virtio_ethdev.h            |   4 +
 drivers/net/virtio/virtio_pci.h               |   8 +
 drivers/net/virtio/virtio_ring.h              |  85 ++++-
 drivers/net/virtio/virtio_rxtx.c              | 360 +++++++++++++++++-
 .../net/virtio/virtio_user/virtio_user_dev.c  |  10 +-
 .../net/virtio/virtio_user/virtio_user_dev.h  |   2 +-
 drivers/net/virtio/virtio_user_ethdev.c       |  14 +-
 drivers/net/virtio/virtqueue.c                |  17 +
 drivers/net/virtio/virtqueue.h                | 113 +++++-
 10 files changed, 630 insertions(+), 33 deletions(-)