netdev - RE: [RFC PATCH 2/2] macvtap: TX zero copy between guest and host kernel

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Message-ID: <F2E9EB7348B8264F86B6AB8151CE2D792B8C815314@shsmsx502.ccr.corp.intel.com>
Date:	Wed, 15 Sep 2010 10:46:02 +0800
From:	"Xin, Xiaohui" <xiaohui.xin@...el.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>,
	Shirley Ma <mashirle@...ibm.com>
CC:	Arnd Bergmann <arnd@...db.de>, Avi Kivity <avi@...hat.com>,
	David Miller <davem@...emloft.net>,
	"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>
Subject: RE: [RFC PATCH 2/2] macvtap: TX zero copy between guest and host
 kernel

>From: Michael S. Tsirkin [mailto:mst@...hat.com]
>Sent: Wednesday, September 15, 2010 12:30 AM
>To: Shirley Ma
>Cc: Arnd Bergmann; Avi Kivity; Xin, Xiaohui; David Miller; netdev@...r.kernel.org;
>kvm@...r.kernel.org; linux-kernel@...r.kernel.org
>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?
>
Michael,
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?

>
>--
>MST
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