linux-kernel - Re: [RFC v4 3/5] virtio_ring: add packed ring support

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Date:   Mon, 21 May 2018 10:30:51 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Tiwei Bie <tiwei.bie@...el.com>
Cc:     mst@...hat.com, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        wexu@...hat.com, jfreimann@...hat.com
Subject: Re: [RFC v4 3/5] virtio_ring: add packed ring support



On 2018年05月19日 10:29, Tiwei Bie wrote:
>> I don't hope so.
>>
>>> I agreed driver should track the DMA addrs or some
>>> other necessary things from the very beginning. And
>>> I also repeated the spec to emphasize that it does
>>> make sense. And I'd like to do that.
>>>
>>> What I was saying is that, to support OOO, we may
>>> need to manage these context (which saves DMA addrs
>>> etc) via a list which is similar to the desc list
>>> maintained via `next` in split ring instead of an
>>> array whose elements always can be indexed directly.
>> My point is these context is a must (not only for OOO).
> Yeah, and I have the exactly same point after you
> pointed that I shouldn't get the addrs from descs.
> I do think it makes sense. I'll do it in the next
> version. I don't have any doubt about it. All my
> questions are about the OOO, instead of whether we
> should save context or not. It just seems that you
> thought I don't want to do it, and were trying to
> convince me that I should do it.

Right, but looks like I was wrong :)

>
>>> The desc ring in split ring is an array, but its
>>> free entries are managed as list via next. I was
>>> just wondering, do we want to manage such a list
>>> because of OOO. It's just a very simple question
>>> that I want to hear your opinion... (It doesn't
>>> means anything, e.g. It doesn't mean I don't want
>>> to support OOO. It's just a simple question...)
>> So the question is yes. But I admit I don't have better idea other than what
>> you propose here (something like split ring which is a little bit sad).
>> Maybe Michael had.
> Yeah, that's why I asked this question. It will
> make the packed ring a bit similar to split ring
> at least in the driver part. So I want to draw
> your attention on this to make sure that we're
> on the same page.

Yes. I think we are.

Thanks

> Best regards,
> Tiwei Bie
>