Subject: Re: [PATCH V3 00/15] Packed virtqueue support for vhost

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 17 Jul 2019 07:02:48 -0400

On Wed, Jul 17, 2019 at 06:52:40AM -0400, Jason Wang wrote:
> Hi all:
> 
> This series implements packed virtqueues which were described
> at [1]. In this version we try to address the performance regression
> saw by V2. The root cause is packed virtqueue need more times of
> userspace memory accesssing which turns out to be very
> expensive. Thanks to the help of 7f466032dc9e ("vhost: access vq
> metadata through kernel virtual address"), such overhead cold be
> eliminated. So in this version, we can see about 2% improvement for
> packed virtqueue on PPS.

Great job, thanks!
Pls allow a bit more review time than usual as this is a big patchset.
Should be done by Tuesday.
-next material anyway.

> More optimizations (e.g IN_ORDER) is on the road.
> 
> Please review.
> 
> [1] https://docs.oasis-open.org/virtio/virtio/v1.1/csprd01/virtio-v1.1-csprd01.html#x1-610007
> 
> This version were tested with:
> - zercopy/datacopy
> - mergeable buffer on/off
> - TCP stream & virtio-user
> 
> Changes from V2:
> - rebase on top of vhost metadata accelreation series
> - introduce shadow used ring API
> - new SET_VRING_BASE/GET_VRING_BASE that takes care about warp counter
>   and index for both avail and used
> - various twaeaks
> 
> Changes from V1:
> - drop uapi patch and use Tiwei's
> - split the enablement of packed virtqueue into a separate patch
> 
> Changes from RFC V5:
> - save unnecessary barriers during vhost_add_used_packed_n()
> - more compact math for event idx
> - fix failure of SET_VRING_BASE when avail_wrap_counter is true
> - fix not copy avail_wrap_counter during GET_VRING_BASE
> - introduce SET_VRING_USED_BASE/GET_VRING_USED_BASE for syncing
> - last_used_idx
> - rename used_wrap_counter to last_used_wrap_counter
> - rebase to net-next
> 
> Changes from RFC V4:
> - fix signalled_used index recording
> - track avail index correctly
> - various minor fixes
> 
> Changes from RFC 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 RFC 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 RFC 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 (15):
>   vhost: simplify meta data pointer accessing
>   vhost: remove the unnecessary parameter of vhost_vq_avail_empty()
>   vhost: remove unnecessary parameter of
>     vhost_enable_notify()/vhost_disable_notify
>   vhost-net: don't use vhost_add_used_n() for zerocopy
>   vhost: introduce helpers to manipulate shadow used ring
>   vhost_net: switch TX to use shadow used ring API
>   vhost_net: calculate last used length once for mergeable buffer
>   vhost_net: switch to use shadow used ring API for RX
>   vhost: do not export vhost_add_used_n() and
>     vhost_add_used_and_signal_n()
>   vhost: hide used ring layout from device
>   vhost: do not use vring_used_elem
>   vhost: vhost_put_user() can accept metadata type
>   vhost: packed ring support
>   vhost: event suppression for packed ring
>   vhost: enable packed virtqueues
> 
>  drivers/vhost/net.c   |  200 +++---
>  drivers/vhost/scsi.c  |   72 +-
>  drivers/vhost/test.c  |    6 +-
>  drivers/vhost/vhost.c | 1508 +++++++++++++++++++++++++++++++++++------
>  drivers/vhost/vhost.h |   78 ++-
>  drivers/vhost/vsock.c |   57 +-
>  6 files changed, 1513 insertions(+), 408 deletions(-)
> 
> -- 
> 2.18.1