Re: [dpdk-dev] [PATCH v3 0/5] vhost add vectorized data path

[Maxime Coquelin <maxime.coquelin@redhat.com>]

Hi Marvin,

On 10/9/20 10:14 AM, Marvin Liu wrote:
> Packed ring format is imported since virtio spec 1.1. All descriptors
> are compacted into one single ring when packed ring format is on. It is
> straight forward that ring operations can be accelerated by utilizing
> SIMD instructions. 
> 
> This patch set will introduce vectorized data path in vhost library. If
> vectorized option is on, operations like descs check, descs writeback,
> address translation will be accelerated by SIMD instructions. On skylake
> server, it can bring 6% performance gain in loopback case and around 4%
> performance gain in PvP case.

IMHO, 4% gain on PVP is not a significant gain if we compare to the
added complexity. Moreover, I guess this is 4% gain with testpmd-based
PVP? If this is the case it may be even lower with OVS-DPDK PVP
benchmark, I will try to do a benchmark this week.

Thanks,
Maxime

> Vhost application can choose whether using vectorized acceleration, just
> like external buffer feature. If platform or ring format not support
> vectorized function, vhost will fallback to use default batch function.
> There will be no impact in current data path.
> 
> v3:
> * rename vectorized datapath file
> * eliminate the impact when avx512 disabled
> * dynamically allocate memory regions structure
> * remove unlikely hint for in_order
> 
> v2:
> * add vIOMMU support
> * add dequeue offloading
> * rebase code
> 
> Marvin Liu (5):
>   vhost: add vectorized data path
>   vhost: reuse packed ring functions
>   vhost: prepare memory regions addresses
>   vhost: add packed ring vectorized dequeue
>   vhost: add packed ring vectorized enqueue
> 
>  doc/guides/nics/vhost.rst           |   5 +
>  doc/guides/prog_guide/vhost_lib.rst |  12 +
>  drivers/net/vhost/rte_eth_vhost.c   |  17 +-
>  lib/librte_vhost/meson.build        |  16 ++
>  lib/librte_vhost/rte_vhost.h        |   1 +
>  lib/librte_vhost/socket.c           |   5 +
>  lib/librte_vhost/vhost.c            |  11 +
>  lib/librte_vhost/vhost.h            | 239 +++++++++++++++++++
>  lib/librte_vhost/vhost_user.c       |  26 +++
>  lib/librte_vhost/virtio_net.c       | 258 ++++-----------------
>  lib/librte_vhost/virtio_net_avx.c   | 344 ++++++++++++++++++++++++++++
>  11 files changed, 718 insertions(+), 216 deletions(-)
>  create mode 100644 lib/librte_vhost/virtio_net_avx.c
>