From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?ISO-8859-1?Q?Roger_Pau_Monn=E9?= <roger.pau@citrix.com>
Subject: Re: Is there data copy between dom0 and domU
Date: Wed, 23 Apr 2014 18:22:19 +0200
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	<20140423161427.GG7712@zion.uk.xensource.com>
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To: Wei Liu <wei.liu2@citrix.com>, xu cong <congxumail@gmail.com>
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On 23/04/14 18:14, Wei Liu wrote:
> 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.

For disks, up to Linux 3.8 data is never copied and starting from 3.8
data can be copied (in the frontend) if both DomU and Dom0 are running
Linux kernel >= 3.8.

Roger.