Re: [dpdk-dev] [PATCH v3 3/5] vhost: add apis for datapath configuration

["Wang, Zhihong" <zhihong.wang@intel.com>]

Hi Maxime,

> -----Original Message-----
> From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
> Sent: Thursday, March 22, 2018 10:19 PM
> To: Wang, Zhihong <zhihong.wang@intel.com>; dev@dpdk.org
> Cc: Tan, Jianfeng <jianfeng.tan@intel.com>; Bie, Tiwei
> <tiwei.bie@intel.com>; yliu@fridaylinux.org; Liang, Cunming
> <cunming.liang@intel.com>; Wang, Xiao W <xiao.w.wang@intel.com>; Daly,
> Dan <dan.daly@intel.com>
> Subject: Re: [PATCH v3 3/5] vhost: add apis for datapath configuration
> 
> Hi,
> 
> On 03/22/2018 09:22 AM, Wang, Zhihong wrote:
> >
> >
> >> -----Original Message-----
> >> From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
> >> Sent: Thursday, March 22, 2018 5:08 AM
> >> To: Wang, Zhihong <zhihong.wang@intel.com>; dev@dpdk.org
> >> Cc: Tan, Jianfeng <jianfeng.tan@intel.com>; Bie, Tiwei
> >> <tiwei.bie@intel.com>; yliu@fridaylinux.org; Liang, Cunming
> >> <cunming.liang@intel.com>; Wang, Xiao W <xiao.w.wang@intel.com>;
> Daly,
> >> Dan <dan.daly@intel.com>
> >> Subject: Re: [PATCH v3 3/5] vhost: add apis for datapath configuration
> >>
> >>
> >>
> >> On 02/27/2018 11:13 AM, Zhihong Wang wrote:
> >>> This patch adds APIs for datapath configuration. The eid and did of the
> >>> vhost-user socket can be configured to identify the actual device.
> >>>
> >>> When the default software datapath is used, eid and did are set to -1.
> >>> When alternative datapath is used, eid and did are set by app to specify
> >>> which device to use. Each vhost-user socket can have only 1 connection
> in
> >>> this case.
> >>>
> >>> Signed-off-by: Zhihong Wang <zhihong.wang@intel.com>
> >>> ---
> >>>    lib/librte_vhost/rte_vhost.h           | 70
> >> ++++++++++++++++++++++++++++++++++
> >>>    lib/librte_vhost/rte_vhost_version.map |  6 +++
> >>>    lib/librte_vhost/socket.c              | 65
> >> +++++++++++++++++++++++++++++++
> >>>    lib/librte_vhost/vhost.c               | 50 ++++++++++++++++++++++++
> >>>    lib/librte_vhost/vhost.h               | 10 +++++
> >>>    5 files changed, 201 insertions(+)
> >>>
> >>
> >> Isn't the notion of EID & DID Intel specifics?
> >> At vhost API level, shouldn't we only care of the offload device ID?
> >
> > It's not vendor specific: Engine id refers to an engine which is a device
> > on a bus, the engine could have multiple queue pairs or virtual functions.
> > The driver can manage them to present multiple vhost ports with vDPA to
> > application, so logically the concept of device id exists.
> >
> > In a lot of acceleration cases, application needs to be able to choose the
> > exact port to use instead of letting the driver to decide (because it does
> > make a difference), therefore it's necessary to expose the device id here.
> 
> Yes, but if I understood correctly with the IFCVF driver, we could pass
> directly the virtual function to the vhost-user lib, no need to specify
> the engine. We would just need to register one device per VF, but that
> looks like the right think to do looking at how IFCVF manages MAC
> addresses and link status for example.

The lib is for generic designs. An engine could also be an AFU device [1]
which has multiple virtio ring compatible queue pairs that can serve
different VMs independently, instead of multiple virtual functions. In
this case, we need eid to index the AFU device, and did to index the queue
pair(s).

[1] http://dpdk.org/ml/archives/dev/2018-March/093343.html (struct rte_afu_device)

Thanks
-Zhihong

> 
> Thanks,
> Maxime