netdev - RE: [RFC PATCH v8 00/16] Provide a zero-copy method on KVM virtio-net.

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Date:	Wed, 4 Aug 2010 10:06:05 +0800
From:	"Dong, Eddie" <eddie.dong@...el.com>
To:	Arnd Bergmann <arnd@...db.de>, Shirley Ma <mashirle@...ibm.com>
CC:	"Xin, Xiaohui" <xiaohui.xin@...el.com>,
	"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>,
	"mst@...hat.com" <mst@...hat.com>, "mingo@...e.hu" <mingo@...e.hu>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
	"jdike@...ux.intel.com" <jdike@...ux.intel.com>,
	"Dong, Eddie" <eddie.dong@...el.com>,
	"Dong, Eddie" <eddie.dong@...el.com>
Subject: RE: [RFC PATCH v8 00/16] Provide a zero-copy method on KVM
 virtio-net.

Arnd Bergmann wrote:
> On Friday 30 July 2010 17:51:52 Shirley Ma wrote:
>> On Fri, 2010-07-30 at 16:53 +0800, Xin, Xiaohui wrote:
>>>> Since vhost-net already supports macvtap/tun backends, do you think
>>>> whether it's better to implement zero copy in macvtap/tun than
>>>> inducing a new media passthrough device here?
>>>> 
>>> 
>>> I'm not sure if there will be more duplicated code in the kernel.
>> 
>> I think it should be less duplicated code in the kernel if we use
>> macvtap to support what media passthrough driver here. Since macvtap
>> has support virtio_net head and offloading already, the only missing
>> func is zero copy. Also QEMU supports macvtap, we just need add a
>> zero copy flag in option.
> 
> Yes, I fully agree and that was one of the intended directions for
> macvtap to start with. Thank you so much for following up on that,
> I've long been planning to work on macvtap zero-copy myself but it's
> now lower on my priorities, so it's good to hear that you made
> progress on it, even if there are still performance issues.
> 

But zero-copy is a Linux generic feature that can be used by other VMMs as well if the BE service drivers want to incorporate.  If we can make mp device VMM-agnostic (it may be not yet in current patch), that will help Linux more.


Thx, Eddie--
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