linux-kernel - Re: [RFC][PATCH v3 1/3] A device for zero-copy based on KVM virtio-net.

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Message-Id: <201004142252.43931.arnd@arndb.de>
Date:	Wed, 14 Apr 2010 22:52:43 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	xiaohui.xin@...el.com, netdev@...r.kernel.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, mingo@...e.hu, davem@...emloft.net,
	jdike@...ux.intel.com
Subject: Re: [RFC][PATCH v3 1/3] A device for zero-copy based on KVM virtio-net.

On Wednesday 14 April 2010 22:40:03 Michael S. Tsirkin wrote:
> On Wed, Apr 14, 2010 at 10:39:49PM +0200, Arnd Bergmann wrote:
> > Well, if the guest not only wants to send data but also receive
> > frames coming from other machines, they need to get from the kernel
> > into qemu, and the only way I can see for doing that is to read
> > from this device if there is no vhost support around on the new
> > machine.
> > 
> > Maybe we're talking about different things here.
>
> mpassthrough is currently useless without vhost.
> If the new machine has no vhost, it can't use mpassthrough :)

Ok. Is that a planned feature though? vhost is currently limited
to guests with a virtio-net driver and even if you extend it to other
guest emulations, it will probably always be a subset of the qemu
supported drivers, but it may be useful to support zero-copy on other
drivers as well.

	Arnd
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