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

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Jun 16, 2017 at 07:04:27PM +0200, Maxime Coquelin wrote:
> 
> 
> On 06/16/2017 05:19 PM, Michael S. Tsirkin wrote:
> > On Fri, Jun 16, 2017 at 04:57:01PM +0800, Jason Wang wrote:
> > > 
> > > 
> > > On 2017年06月16日 11:22, Michael S. Tsirkin wrote:
> > > > > I think the issues can be solved by VIRTIO_F_MAX_CHAIN_SIZE.
> > > > > 
> > > > > For now, how about splitting it into two series of patches:
> > > > > 1) enable 1024 tx queue size for vhost-user, to let the users of vhost-user
> > > > > to easily use 1024 queue size.
> > > > Fine with me. 1) will get property from user but override it on
> > > > !vhost-user. Do we need a protocol flag? It seems prudent but we get
> > > > back to cross-version migration issues that a04re still pending solution.
> > > > Marc Andre, what's the status of that work?
> > > > 
> > > > > 2) enable VIRTIO_F_MAX_CHAIN_SIZE,  to enhance robustness.
> > > > Rather, to support it for more backends.
> > > 
> > > Ok, if we want to support different values of max chain size in the future.
> > > It would be problematic for migration of cross backends, consider the case
> > > when migrating from 2048 (vhost-user) to 1024 (qemu/vhost-kernel).
> > > 
> > > Thanks
> > 
> > That's already a problem, and it's growing with each new feature.
> > Maxime looked at supporting vhost-user backends cross-version migration,
> > I think we must merge some solution sooner rather than later, preferably
> > by the next release.
> > 
> > Maxime, any update here? Do we need a meeting to reach consensus?
> 
> No update, I haven't found time to progress on the topic yet.
> 
> For those who aren't aware of my initial proposal, you may find it here:
> https://www.spinics.net/linux/fedora/libvir/msg142668.html
> 
> If my understanding is correct, you were concerned about the complexity of
> my
> proposal which involved too many layers. Your suggestion was to have a tool
> provided with qemu that would connect to vhost-user socket and query the
> backend capabilities.
> I'm not 100% clear how it would work, as the trend is to start the backend
> in
> client mode, meaning QEMU creates the socket. In this case, should the tool
> create the socket and management tool request the backend to connect to it?
> 
> I think it could make sense to have a meeting, but maybe we should first
> discuss the solutions on the list for efficiency.
> 
> For the delivery, what is QEMU v2.10 planned release date?
> 
> Note that my solution doesn't involve QEMU, so it would not be tight to QEMU
> release date. But, that doesn't mean it would be delivered sooner than
> your solution.
> 
> Maxime

I'd say let's go with your proposal (Solution 3 above).

-- 
MST