Re: [dpdk-dev] [RFC] Accelerating Data Movement for DPDK vHost with DMA Engines

[Jerin Jacob <jerinjacobk@gmail.com>]

On Mon, Apr 20, 2020 at 5:14 PM Maxime Coquelin
<maxime.coquelin@redhat.com> wrote:
>
>
>
> On 4/20/20 1:13 PM, Jerin Jacob wrote:
> > On Mon, Apr 20, 2020 at 1:29 PM Liang, Cunming <cunming.liang@intel.com> wrote:
> >>
> >>
> >>
> >>> -----Original Message-----
> >>> From: Jerin Jacob <jerinjacobk@gmail.com>
> >>> Sent: Friday, April 17, 2020 5:55 PM
> >>> To: Fu, Patrick <patrick.fu@intel.com>
> >>> Cc: Maxime Coquelin <maxime.coquelin@redhat.com>; dev@dpdk.org; Ye,
> >>> Xiaolong <xiaolong.ye@intel.com>; Hu, Jiayu <jiayu.hu@intel.com>; Wang,
> >>> Zhihong <zhihong.wang@intel.com>; Liang, Cunming <cunming.liang@intel.com>
> >>> Subject: Re: [dpdk-dev] [RFC] Accelerating Data Movement for DPDK vHost with
> >>> DMA Engines
> >>>
> >>> On Fri, Apr 17, 2020 at 2:56 PM Fu, Patrick <patrick.fu@intel.com> wrote:
> >>>>
> >>>>
> >> [...]
> >>>>>>
> >>>>>> I believe it doesn't conflict. The purpose of this RFC is to
> >>>>>> create an async
> >>>>> data path in vhost-user and provide a way for applications to work
> >>>>> with this new path. dmadev is another topic which could be discussed
> >>>>> separately. If we do have the dmadev available in the future, this
> >>>>> vhost async data path could certainly be backed by the new dma
> >>>>> abstraction without major interface change.
> >>>>>
> >>>>> Maybe that one advantage of a dmadev class is that it would be
> >>>>> easier and more transparent for the application to consume.
> >>>>>
> >>>>> The application would register some DMA devices, pass them to the
> >>>>> Vhost library, and then rte_vhost_submit_enqueue_burst and
> >>>>> rte_vhost_poll_enqueue_completed would call the dmadev callbacks directly.
> >>>>>
> >>>>> Do you think that could work?
> >>>>>
> >>>> Yes, this is a workable model. As I said in previous reply, I have no objection to
> >>> make the dmadev. However, what we currently want to do is creating the async
> >>> data path for vhost, and we actually have no preference to the underlying DMA
> >>> device model. I believe our current design of the API proto type /data structures
> >>> are quite common for various DMA acceleration solutions and there is no blocker
> >>> for any new DMA device to adapt to these APIs or extend to a new one.
> >>>
> >>> IMO, as a driver writer,  we should not be writing TWO DMA driver. One for vhost
> >>> and other one for rawdev.
> >> It's the most simplest case if statically 1:1 mapping driver (e.g. {port, queue}) to a vhost session {vid, qid}. However, it's not enough scalable to integrate device model with vhost library. There're a few intentions belong to app logic rather than driver, e.g. 1:N load balancing, various device type usages (e.g. vhost zcopy via ethdev) and etc.
> >
> >
> > Before moving to reply to comments, Which DMA engine you are planning
> > to integrate with vHOST?
> > Is is ioat? if not ioat(drivers/raw/ioat/), How do you think, how we
> > can integrate this IOAT DMA engine to vHOST as a use case?
> >
>
> I guess it could be done in the vhost example.


Could not see any reference to DMA in  examples/vhost*