linux-kernel - RE: [PATCH 0/3] Provide a zero-copy method on KVM virtio-net.

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Date:	Thu, 11 Feb 2010 15:40:08 +0800
From:	"Xin, Xiaohui" <xiaohui.xin@...el.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>, "mst@...hat.com" <mst@...hat.com>,
	"jdike@...user-mode-linux.org" <jdike@...user-mode-linux.org>
Subject: RE: [PATCH 0/3] Provide a zero-copy method on KVM virtio-net.

>>On Wednesday 10 February 2010, Xin Xiaohui wrote:
> >The idea is simple, just to pin the guest VM user space and then
> >let host NIC driver has the chance to directly DMA to it. 
> >The patches are based on vhost-net backend driver. We add a device
> >which provides proto_ops as sendmsg/recvmsg to vhost-net to
> >send/recv directly to/from the NIC driver. KVM guest who use the
> >vhost-net backend may bind any ethX interface in the host side to
> >get copyless data transfer thru guest virtio-net frontend.
>> 
>> We provide multiple submits and asynchronous notifiicaton to 
> >vhost-net too.

>This does a lot of things that I had planned for macvtap. It's
>great to hear that you have made this much progress.
>
>However, I'd hope that we could combine this with the macvtap driver,
>which would give us zero-copy transfer capability both with and
>without vhost, as well as (tx at least) when using multiple guests
>on a macvlan setup.

You mean the zero-copy can work with macvtap driver without vhost.
May you give me some detailed info about your macvtap driver and the
relationship between vhost and macvtap to make me have a clear picture then?

>For transmit, it should be fairly straightforward to hook up
>your zero-copy method and the vhost-net interface into the
>macvtap driver.
>
>You have simplified the receiv path significantly by assuming
>that the entire netdev can receive into a single guest, right?

Yes.

>I'm assuming that the idea is to allow VMDq adapters to simply
>show up as separate adapters and have the driver handle this
>in a hardware specific way.

Does the VMDq driver do so now?

>My plan for this was to instead move support for VMDq into the
>macvlan driver so we can transparently use VMDq on hardware where
>available, including zero-copy receives, but fall back to software
>operation on non-VMDq hardware.

	Arnd
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