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

On Mon, May 21, 2018 at 10:30:51AM +0800, Jason Wang wrote:

On 2018年05月19日 10:29, Tiwei Bie wrote:

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I don't hope so.

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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 :)

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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.

Cool. Glad to hear that! Thanks! :)

Best regards,
Tiwei Bie

Thanks

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Best regards,
Tiwei Bie