Re: [Qemu-devel] [virtio-dev] Re: [PATCH v1] virtio-net: enable configurable tx queue size

[Jason Wang]

On 2017年06月13日 11:51, Wei Wang wrote:
> On 06/13/2017 11:19 AM, Jason Wang wrote:
> > On 2017年06月13日 11:10, Wei Wang wrote:
> > > On 06/13/2017 04:43 AM, Michael S. Tsirkin wrote:
> > > > On Mon, Jun 12, 2017 at 05:30:46PM +0800, Wei Wang wrote:
> > > > > Ping for comments, thanks.
> > > > This was only posted a week ago, might be a bit too short for some
> > > > people.
> > > OK, sorry for the push.
> > > > A couple of weeks is more reasonable before you ping.  Also, I
> > > > sent a bunch of comments on Thu, 8 Jun 2017.  You should probably
> > > > address these.
> > > I responded to the comments. The main question is that I'm not sure
> > > why we need the vhost backend to support VIRTIO_F_MAX_CHAIN_SIZE.
> > > IMHO, that should be a feature proposed to solve the possible issue
> > > caused by the QEMU implemented backend.
> >
> > The issue is what if there's a mismatch of max #sgs between qemu and 
> > vhost?
>
> When the vhost backend is used, QEMU is not involved in the data path. 
> The vhost backend
> directly gets what is offered by the guest from the vq. Why would 
> there be a mismatch of
> max #sgs between QEMU and vhost, and what is the QEMU side max #sgs 
> used for? Thanks.

You need query the backend max #sgs in this case at least. no? If not 
how do you know the value is supported by the backend?

Thanks

> Best,
> Wei