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Subject: Re: [PATCH RFC 00/15] Add VFIO mediated device support and IMS
 support for the idxd driver.
To:     Jason Gunthorpe <jgg@mellanox.com>,
        "Raj, Ashok" <ashok.raj@intel.com>
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        "hpa@zytor.com" <hpa@zytor.com>,
        "Pan, Jacob jun" <jacob.jun.pan@intel.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>, "Lu, Baolu" <baolu.lu@intel.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@intel.com>,
        "Luck, Tony" <tony.luck@intel.com>,
        "Lin, Jing" <jing.lin@intel.com>,
        "Williams, Dan J" <dan.j.williams@intel.com>,
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        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>
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From:   Jason Wang <jasowang@redhat.com>
Message-ID: <196b23b9-12f7-2fc2-5efb-22e0642c456a@redhat.com>
Date:   Wed, 13 May 2020 10:29:31 +0800
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On 2020/5/9 下午8:21, Jason Gunthorpe wrote:
> On Fri, May 08, 2020 at 05:09:09PM -0700, Raj, Ashok wrote:
>> Hi Jason
>>
>> On Fri, May 08, 2020 at 08:16:10PM -0300, Jason Gunthorpe wrote:
>>> On Fri, May 08, 2020 at 01:47:10PM -0700, Raj, Ashok wrote:
>>>
>>>> Even when uaccel was under development, one of the options
>>>> was to use VFIO as the transport, goal was the same i.e to keep
>>>> the user space have one interface.
>>> I feel a bit out of the loop here, uaccel isn't in today's kernel is
>>> it? I've heard about it for a while, it sounds very similar to RDMA,
>>> so I hope they took some of my advice...
>> I think since 5.7 maybe? drivers/misc/uacce. I don't think this is like
>> RDMA, its just a plain accelerator. There is no connection management,
>> memory registration or other things.. IB was my first job at Intel,
>> but saying that i would be giving my age away:)
> rdma was the first thing to do kernel bypass, all this stuff is like
> rdma at some level.. I see this looks like the 'warp driver' stuff
> redone
>
> Wow, lots wrong here. Oh well.
>
>>> putting emulation code back into them, except in a more dangerous
>>> kernel location. This does not seem like a net win to me.
>> Its not a whole lot of emulation right? mdev are soft partitioned. There is
>> just a single PF, but we can create a separate partition for the guest using
>> PASID along with the normal BDF (RID). And exposing a consistent PCI like
>> interface to user space you get everything else for free.
>>
>> Yes, its not SRIOV, but giving that interface to user space via VFIO, we get
>> all of that functionality without having to reinvent a different way to do it.
>>
>> vDPA went the other way, IRC, they went and put a HW implementation of what
>> virtio is in hardware. So they sort of fit the model. Here the instance
>> looks and feels like real hardware for the setup and control aspect.
> VDPA and this are very similar, of course it depends on the exact HW
> implementation.
>
> Jason


Actually this is not a must. Technically we can do ring/descriptor 
translation in the vDPA driver as what zerocopy AF_XDP did.

Thanks


>