[RFC V5 PATCH 0/8] Packed ring layout for vhost

[Jason Wang]

Hi all:

This RFC implement packed ring layout. The code were tested with
Tiwei's RFC V5 at https://lkml.org/lkml/2018/5/22/138. Some fixups and
tweaks were needed on top of Tiwei's code to make it run for event
index.

Pktgen reports about 20% improvement on TX PPS when doing pktgen from
guest to host. No ovbious improvement on RX PPS. We can do lots of
optimizations on top but for simple and for correceness first, this
version does not do much.

This version were tested with:

- Zerocopy (Out of Order) support
- vIOMMU support
- mergeable buffer on/off
- busy polling on/off

Notes for tester:

- Start from this version, vhost need qemu co-operation to work
  correctly. Or you can comment out the packed specific code for
  GET/SET_VRING_BASE.

- Changes from V4:
- fix signalled_used index recording
- track avail index correctly
- various minor fixes

Changes from V3:
- Fix math on event idx checking
- Sync last avail wrap counter through GET/SET_VRING_BASE
- remove desc_event prefix in the driver/device structure

Changes from V2:
- do not use & in checking desc_event_flags
- off should be most significant bit
- remove the workaround of mergeable buffer for dpdk prototype
- id should be in the last descriptor in the chain
- keep _F_WRITE for write descriptor when adding used
- device flags updating should use ADDR_USED type
- return error on unexpected unavail descriptor in a chain
- return false in vhost_ve_avail_empty is descriptor is available
- track last seen avail_wrap_counter
- correctly examine available descriptor in get_indirect_packed()
- vhost_idx_diff should return u16 instead of bool

Changes from V1:

- Refactor vhost used elem code to avoid open coding on used elem
- Event suppression support (compile test only).
- Indirect descriptor support (compile test only).
- Zerocopy support.
- vIOMMU support.
- SCSI/VSOCK support (compile test only).
- Fix several bugs

Jason Wang (8):
  vhost: move get_rx_bufs to vhost.c
  vhost: hide used ring layout from device
  vhost: do not use vring_used_elem
  vhost_net: do not explicitly manipulate vhost_used_elem
  vhost: vhost_put_user() can accept metadata type
  virtio: introduce packed ring defines
  vhost: packed ring support
  vhost: event suppression for packed ring

 drivers/vhost/net.c                | 144 ++----
 drivers/vhost/scsi.c               |  62 +--
 drivers/vhost/vhost.c              | 926 +++++++++++++++++++++++++++++++++----
 drivers/vhost/vhost.h              |  52 ++-
 drivers/vhost/vsock.c              |  42 +-
 include/uapi/linux/virtio_config.h |   9 +
 include/uapi/linux/virtio_ring.h   |  32 ++
 7 files changed, 1000 insertions(+), 267 deletions(-)

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2.7.4