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 5:57 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 10/12/20 11:10 AM, Liu, Yong wrote:
> >
> >
> >> -----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 for the information.
> 
> Also, wouldn't using AVX512 lower the CPU frequency?
> If so, could it have an impact on the workload running on the other
> CPUs?
> 

All AVX512 instructions used in vhost are lightweight ones, frequency won't be affected. 
Theoretically system performance won’t be affected if only lightweight instructions are used. 

Thanks.

> Thanks,
> Maxime
> 
> >> 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
> >>>
> >