netdev - Re: [PATCH v3 3/6] vbus: add a "vbus-proxy" bus model for vbus

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Date:	Mon, 17 Aug 2009 08:54:26 -0500
From:	Anthony Liguori <anthony@...emonkey.ws>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Gregory Haskins <ghaskins@...ell.com>, kvm@...r.kernel.org,
	Avi Kivity <avi@...hat.com>,
	alacrityvm-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	"Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH v3 3/6] vbus: add a "vbus-proxy" bus model for vbus_driver
 objects

Ingo Molnar wrote:
>> I think the reason vbus gets better performance for networking 
>> today is that vbus' backends are in the kernel while virtio's 
>> backends are currently in userspace.  Since Michael has a 
>> functioning in-kernel backend for virtio-net now, I suspect we're 
>> weeks (maybe days) away from performance results.  My expectation 
>> is that vhost + virtio-net will be as good as venet + vbus.  If 
>> that's the case, then I don't see any reason to adopt vbus unless 
>> Greg things there are other compelling features over virtio.
>>     
>
> Keeping virtio's backend in user-space was rather stupid IMHO. 
>   

I don't think it's quite so clear.

There's nothing about vhost_net that would prevent a userspace 
application from using it as a higher performance replacement for tun/tap.

The fact that we can avoid userspace for most of the fast paths is nice 
but that's really an issue of vhost_net vs. tun/tap.

 From the kernel's perspective, a KVM guest is just a userspace 
process.  Having new userspace interfaces that are only useful to KVM 
guests would be a bad thing.

Regards,

Anthony Liguori
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