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Re: [Xen-devel] Is there data copy between dom0 and domU

To: xu cong <congxumail@xxxxxxxxx>
From: Wei Liu <wei.liu2@xxxxxxxxxx>
Date: Wed, 23 Apr 2014 17:14:27 +0100
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxx
Delivery-date: Wed, 23 Apr 2014 16:14:43 +0000
List-id: Xen developer discussion <xen-devel.lists.xen.org>

On Wed, Apr 23, 2014 at 12:06:51PM -0400, xu cong wrote:
> When applications running in domU receive/send data from/to network, is
> there data copy via shared memory between dom0 and domU? Or the zero copy
> is used. How about the disk I/O operations? Thanks.

If you're using latest kernel (3.14-ish), guest TX path is zero-copy,
otherwise it's using copy. For RX path it always copies.

I think disk always copies data. But I'm not sure.

Wei.

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