[Qemu-devel] [PATCH v2 00/15] packed ring virtio-net backends support

[wexu@redhat.com]

From: Wei Xu <wexu@redhat.com>

v1->v2:
 - fix patchew complaint
 - only set/get last_avail_idx/wrap_counter for vhost migration(Maxime)
 - replace 'out_num' and 'in_num' with 'elem_entries'in packed_pop()(Maxime)
 - set last used idx/wrap_counter to last avail ones when flushing(Maxime)
 - replace '*host_has_feature()' with '*vdev_has_feature()' for ioctl(Maxime)
 - replace going through indirect descriptors with desc.len/sizeof(desc)(btw)
 - add new subsection for packed ring(Jason)

rfc v3 -> v1
- migration support for both userspace and vhost-net, need tweak vhost
  ioctl() to make it work(the code is pasted in the commit message of
  vhost migration patch #13).

Note:
  the high 32-bit guest feature bit is saved as a subsection for
  virtio devices which makes packed ring feature bit check unusable when
  loading the saved per-queue variables(this is done before loading
  subsection which is the last action for device during migration),
  so I save and load all the things generally for now, any idea to fix this?

- Fixed comments from Jason for rfc v3 sorted by patch #, two comments I
  didn't take were(from patch) listed here:
09: - introduce new API(virtqueue_fill_n()).
      - Didn't take it since userspace backend does not support batching,
        so only one element is popped and current API should be enough.
06 & 07: Refactor split and packed pop()/get_avail_bytes().
         - the duplicated code interwined with split/packed ring specific
           things and it might make it unclear, so I only extracted the few
           common parts out side rcu and keep the others separate.

The other revised comments:
02: - reuse current 'avail/used' for 'driver/device' in VRingMemoryRegionCache.
    - remove event_idx since shadow_avail_idx works.
03: - move size recalculation to a separate patch.
    - keep 'avail/used' in current calculation function name.
    - initialize 'desc' memory region as 'false' for 1.0('true' for 1.1)
04: - delete 'event_idx'
05: - rename 'wc' to wrap_counter.
06: - converge common part outside rcu section for 1.0/1.1.
    - move memory barrier for the first 'desc' in between checking flag
      and read other fields.
    - remove unnecessary memory barriers for indirect descriptors.
    - no need to destroy indirect memory cache since it is generally done
      before return from the function.
    - remove redundant maximum chained descriptors limitation check.
    - there are some differences(desc name, wrap idx/counter, flags) between
      split and packed rings, so keep them separate for now.
    - amend the comment when recording index and wrap counter for a kick
      from guest.
07: - calculate fields in descriptor instead of read it when filling.
    - put memory barrier correctly before filling the flags in descriptor.
    - replace full memory barrier with a write barrier in fill.
    - shift to read descriptor flags and descriptor necessarily and
      separately in packed_pop().
    - correct memory barrier in packed_pop() as in packed_fill().
08: - reuse 'shadow_avail_idx' instead of adding a new 'event_idx'.
    - use the compact and verified vring_packed_need_event()
      version for vhost net/user.
12: - remove the odd cherry-pick comment.
    - used bit '15' for wrap_counters.

rfc v2->v3
- addressed performance issue
- fixed feedback from v2

rfc v1->v2
- sync to tiwei's v5
- reuse memory cache function with 1.0
- dropped detach patch and notification helper(04 & 05 in v1)
- guest virtio-net driver unload/reload support
- event suppression support(not tested)
- addressed feedback from v1


Wei Xu (15):
  virtio: introduce packed ring definitions
  virtio: redefine structure & memory cache for packed ring
  virtio: expand offset calculation for packed ring
  virtio: add memory region init for packed ring
  virtio: init wrap counter for packed ring
  virtio: init and desc empty check for packed ring
  virtio: get avail bytes check for packed ring
  virtio: fill/flush/pop for packed ring
  virtio: event suppression support for packed ring
  virtio-net: fill head desc after done all in a chain
  virtio: add userspace migration for packed ring
  virtio: add vhost-net migration for packed ring
  virtio: packed ring feature bit for userspace backend
  vhost: enable packed ring
  virtio: enable packed ring via a new command line

 hw/net/vhost_net.c                             |   2 +
 hw/net/virtio-net.c                            |  11 +-
 hw/virtio/virtio.c                             | 774 +++++++++++++++++++++++--
 include/hw/virtio/virtio.h                     |   4 +-
 include/standard-headers/linux/virtio_config.h |  15 +
 include/standard-headers/linux/virtio_ring.h   |  43 ++
 6 files changed, 800 insertions(+), 49 deletions(-)

-- 
1.8.3.1