[dpdk-dev] [RFC PATCH v2] vhost: Add VHOST PMD

[Tetsuya Mukawa]

On 2015/10/19 18:45, Bruce Richardson wrote:
> On Mon, Oct 19, 2015 at 10:32:50AM +0100, Loftus, Ciara wrote:
>>> On 2015/10/16 21:52, Bruce Richardson wrote:
>>>> On Mon, Aug 31, 2015 at 12:55:26PM +0900, Tetsuya Mukawa wrote:
>>>>> The patch introduces a new PMD. This PMD is implemented as thin
>>> wrapper
>>>>> of librte_vhost. It means librte_vhost is also needed to compile the PMD.
>>>>> The PMD can have 'iface' parameter like below to specify a path to
>>> connect
>>>>> to a virtio-net device.
>>>>>
>>>>> $ ./testpmd -c f -n 4 --vdev 'eth_vhost0,iface=/tmp/sock0' -- -i
>>>>>
>>>>> To connect above testpmd, here is qemu command example.
>>>>>
>>>>> $ qemu-system-x86_64 \
>>>>>         <snip>
>>>>>         -chardev socket,id=chr0,path=/tmp/sock0 \
>>>>>         -netdev vhost-user,id=net0,chardev=chr0,vhostforce \
>>>>>         -device virtio-net-pci,netdev=net0
>>>>>
>>>>> Signed-off-by: Tetsuya Mukawa <mukawa at igel.co.jp>
>>>> With this PMD in place, is there any need to keep the existing vhost library
>>>> around as a separate entity? Can the existing library be
>>> subsumed/converted into
>>>> a standard PMD?
>>>>
>>>> /Bruce
>>> Hi Bruce,
>>>
>>> I concern about whether the PMD has all features of librte_vhost,
>>> because librte_vhost provides more features and freedom than ethdev API
>>> provides.
>>> In some cases, user needs to choose limited implementation without
>>> librte_vhost.
>>> I am going to eliminate such cases while implementing the PMD.
>>> But I don't have strong belief that we can remove librte_vhost now.
>>>
>>> So how about keeping current separation in next DPDK?
>>> I guess people will try to replace librte_vhost to vhost PMD, because
>>> apparently using ethdev APIs will be useful in many cases.
>>> And we will get feedbacks like "vhost PMD needs to support like this usage".
>>> (Or we will not have feedbacks, but it's also OK.)
>>> Then, we will be able to merge librte_vhost and vhost PMD.
>> I agree with the above. One the concerns I had when reviewing the patch was that the PMD removes some freedom that is available with the library. Eg. Ability to implement the new_device and destroy_device callbacks. If using the PMD you are constrained to the implementations of these in the PMD driver, but if using librte_vhost, you can implement your own with whatever functionality you like - a good example of this can be seen in the vhost sample app.
>> On the other hand, the PMD is useful in that it removes a lot of complexity for the user and may work for some more general use cases. So I would be in favour of having both options available too.
>>
>> Ciara
>>
> Thanks.
> However, just because the libraries are merged does not mean that you need
> be limited by PMD functionality. Many PMDs provide additional library-specific
> functions over and above their PMD capabilities. The bonded PMD is a good example
> here, as it has a whole set of extra functions to create and manipulate bonded
> devices - things that are obviously not part of the general ethdev API. Other
> vPMDs similarly include functions to allow them to be created on the fly too.
>
> regards,
> /Bruce

Hi Bruce,

I appreciate for showing a good example. I haven't noticed the PMD.
I will check the bonding PMD, and try to remove librte_vhost without
losing freedom and features of the library.

Regards,
Tetsuya