Re: [dpdk-dev] [PATCH v5 0/6] Virtio-net PMD: QEMU QTest extension for container

[Tetsuya Mukawa <mukawa@igel.co.jp>]

On 2016/06/06 16:21, Yuanhan Liu wrote:
> On Mon, Jun 06, 2016 at 02:10:46PM +0900, Tetsuya Mukawa wrote:
>> Hi Yuanhan,
>>
>> Sorry for late replying.
> 
> Never mind.
> 
>>
>> On 2016/06/03 13:17, Yuanhan Liu wrote:
>>> On Thu, Jun 02, 2016 at 06:30:18PM +0900, Tetsuya Mukawa wrote:
>>>> Hi Yuanhan,
>>>>
>>>> On 2016/06/02 16:31, Yuanhan Liu wrote:
>>>>> But still, I'd ask do we really need 2 virtio for container solutions?
>>>>
>>>> I appreciate your comments.
>>>
>>> No, I appreciate your effort for contributing to DPDK! vhost-pmd stuff
>>> is just brilliant!
>>>
>>>> Let me have time to discuss it with our team.
>>>
>>> I'm wondering could we have one solution only. IMO, the drawback of
>>> having two (quite different) solutions might outweighs the benefit
>>> it takes. Say, it might just confuse user.
>>
>> I agree with this.
>> If we have 2 solutions, it would confuse the DPDK users.
>>
>>>
>>> OTOH, I'm wondering could you adapt to Jianfeng's solution? If not,
>>> what's the missing parts, and could we fix it? I'm thinking having
>>> one unified solution will keep ours energy/focus on one thing, making
>>> it better and better! Having two just splits the energy; it also
>>> introduces extra burden for maintaining.
>>
>> Of course, I adopt Jiangeng's solution basically.
>> Actually, his solution is almost similar I tried to implement at first.
>>
>> I guess here is pros/cons of 2 solutions.
>>
>> [Jianfeng's solution]
>> - Pros
>> Don't need to invoke QEMU process.
>> - Cons
>> If virtio-net specification is changed, we need to implement it by
>> ourselves. Also, LSC interrupt and control queue functions are not
>> supported yet.
> 
> Jianfeng have made and sent out the patch to enable ctrl queue and
> multiple queue support.

Sorry, I haven't noticed that ctrl queue has been already enabled.

> 
> For the LSC part, no much idea yet so far. But I'm assuming it will
> not take too much effort, either.
> 
>> I agree both functions may not be so important, and if we need it
>> we can implement them, but we need to pay energy to implement them.
>>
>> [My solution]
>> - Pros
>> Basic principle of my implementation is not to reinvent the wheel.
> 
> Yes, that's a good point. However, it's not that hard as we would have
> thought in the first time: the tough part that dequeue/enqueue packets
> from/to vring is actually offloaded to DPDK vhost-user. That means we
> only need re-implement the control path of virtio-net device, plus the
> vhost-user frontend. If you have a detailed look of your patchset as
> well Jianfeng's, you might find that the two patchset are actually with
> same code size. 

Yes, I know this.
So far, the amount of code is almost same, but in the future we may need
to implement more, if virtio-net specification is revised.

> 
>> We can use a virtio-net device of QEMU implementation, it means we don't
>> need to maintain virtio-net device by ourselves, and we can use all of
>> functions supported by QEMU virtio-net device.
>> - Cons
>> Need to invoke QEMU process.
> 
> Another thing is that it makes the usage a bit harder: look at the
> long qemu cli options of your example usage. It also has some traps,
> say, "--enable-kvm" is not allowed, which is a default option used
> with QEMU.

Probably a kind of shell script will help the users.

> 
> And judging that we actually don't take too much effort to implement
> a virtio device emulation, I'd prefer it slightly. I guess something
> light weight and easier for use is more important here.

This is very important point.
If so, we don't need much effort when virtio-spec is changed.

> 
> Actually, I have foreseen another benefit of adding virtio-user device
> emulation: we now might be able to add a rte_vhost_dequeue/enqueue_burst()
> unit test case. We simply can't do it before, since we depend on QEMU
> for testing, which is not acceptable for a unit test case. Making it
> be a unit test case would help us spotting any bad changes that would
> introduce bugs easily and automatically.

As you mentioned above, QEMU process is not related with
dequeuing/enqueuing.
So I guess we may have a testing for rte_vhost_dequeue/enqueue_burst()
regardless of choice.

>> Anyway, we can choose one of belows.
>> 1. Take advantage of invoking less processes.
>> 2. Take advantage of maintainability of virtio-net device.

If container usage that DPDK assumes is to invoke hundreds containers in
one host, we should take Jiangfeng's solution.

Also, if implementing a new feature and maintaining Jiangfeng's
virtio-net device are not so hard, we should take his solution.

I guess this is the point we need to consider.
What do you think?

Thanks,
Tetsuya

>>
>> Honestly, I'm OK if my solution is not merged.
>> Thus, it should be decided to let DPDK better.
>>
>> What do you think?
>> Which is better for DPDK?
>>
>> Thanks,
>> Tetsuya
>>
>>>
>>> 	--yliu
>>>