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Date:	Wed, 15 Sep 2010 10:46:02 +0800
From:	"Xin, Xiaohui" <>
To:	"Michael S. Tsirkin" <>,
	Shirley Ma <>
CC:	Arnd Bergmann <>, Avi Kivity <>,
	David Miller <>,
	"" <>,
	"" <>,
	"" <>
Subject: RE: [RFC PATCH 2/2] macvtap: TX zero copy between guest and host

>From: Michael S. Tsirkin []
>Sent: Wednesday, September 15, 2010 12:30 AM
>To: Shirley Ma
>Cc: Arnd Bergmann; Avi Kivity; Xin, Xiaohui; David Miller;;
>Subject: Re: [RFC PATCH 2/2] macvtap: TX zero copy between guest and host kernel
>On Tue, Sep 14, 2010 at 09:00:25AM -0700, Shirley Ma wrote:
>> On Tue, 2010-09-14 at 17:22 +0200, Michael S. Tsirkin wrote:
>> > I would expect this to hurt performance significantly.
>> > We could do this for asynchronous requests only to avoid the
>> > slowdown.
>> Is kiocb in sendmsg helpful here? It is not used now.
>> Shirley
>Precisely. This is what the patch from Xin Xiaohui does.  That code
>already seems to do most of what you are trying to do, right?
>The main thing missing seems to be macvtap integration, so that we can fall back
>on data copy if zero copy is unavailable?
>How hard would it be to basically link the mp and macvtap modules
>together to get us this functionality? Anyone?
Is to support macvtap with zero-copy through mp device the functionality
you mentioned above?
Before Shirley Ma has suggested to move the zero-copy functionality into
tun/tap device or macvtap device. How do you think about that? I suspect
there will be a lot of duplicate code in that three drivers except we can extract
code of zero-copy into kernel APIs and vhost APIs.
Do you think that's worth to do and help current process which is blocked too
long than I expected?

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