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

From: Tiwei Bie <tiwei.bie@intel.com>
To: Jason Wang <jasowang@redhat.com>
Cc: mst@redhat.com, virtualization@lists.linux-foundation.org,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	wexu@redhat.com, jfreimann@redhat.com
Subject: Re: [RFC v4 3/5] virtio_ring: add packed ring support
Date: Mon, 21 May 2018 10:39:44 +0800	[thread overview]
Message-ID: <20180521023944.GA16702@debian> (raw)
In-Reply-To: <b8c0d147-2711-cb26-a084-e7d3d32d0002@redhat.com>

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:
> > > 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.

Cool. Glad to hear that! Thanks! :)

Best regards,
Tiwei Bie

> 
> Thanks
> 
> > Best regards,
> > Tiwei Bie
> > 
> 