[PATCH RFC 0/2] Packed ring for vhost

Hi all:

This RFC implement a subset of packed ring which was described at
https://github.com/oasis-tcs/virtio-docs/blob/master/virtio-v1.1-packed-wd07.pdf
. The code were tested with pmd implement by Jens at
http://dpdk.org/ml/archives/dev/2018-January/089417.html. Minor
change was needed for pmd codes to kick virtqueue since it assumes a
busy polling backend.

Test were done between localhost and guest. Testpmd (rxonly) in guest
reports 2.4Mpps. Testpmd (txonly) repots about 2.1Mpps.

It's not a complete implemention, here's what were missed:

- Device Area
- Driver Area
- Descriptor indirection
- Zerocopy may not be functional
- Migration path is not tested
- Vhost devices except for net
- vIOMMU can not work (mainly because the metadata prefetch is not
  implemented).
- See FIXME/TODO in the codes for more details
- No batching or other optimizations were implemented

For a quick prototype, this series open code the tracking of warp
counter and descriptor index at net device. This will be addressed in
the future by:

- Move get_rx_bufs() from net.c to vhost.c
- Let vhost_get_vq_desc() returns vring_used_elem instad of head id

With the above, we can hide the internal (at least part of) vring
layout from specific device.

Please review.

Thanks

Jason Wang (2):
  virtio: introduce packed ring defines
  vhost: packed ring support

 drivers/vhost/net.c                |  14 +-
 drivers/vhost/vhost.c              | 351 ++++++++++++++++++++++++++++++++++---
 drivers/vhost/vhost.h              |   6 +-
 include/uapi/linux/virtio_config.h |   9 +
 include/uapi/linux/virtio_ring.h   |  17 ++
 5 files changed, 369 insertions(+), 28 deletions(-)

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2.7.4