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

["Liu, Yong" <yong.liu@intel.com>]

> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: Monday, October 12, 2020 4:22 PM
> To: Liu, Yong <yong.liu@intel.com>; Xia, Chenbo <chenbo.xia@intel.com>;
> Wang, Zhihong <zhihong.wang@intel.com>
> Cc: dev@dpdk.org
> Subject: Re: [PATCH v3 0/5] vhost add vectorized data path
> 
> 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.
> 

Maxime, 
I have observed around 3% gain with OVS-DPDK in first version. But the number is not reliable as datapath has been changed. 
I will try again after fixed OVS integration issue with latest dpdk. 

> 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
> >