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

quoted

On Tue, 2010-09-14 at 17:22 +0200, Michael S. Tsirkin wrote:

quoted

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