Re: [Xen-devel] How to detect HAP from DomU?

To:	"Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>
Subject:	Re: [Xen-devel] How to detect HAP from DomU?
From:	Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>
Date:	Wed, 10 Nov 2010 09:49:51 +0100
Cc:	"xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir@xxxxxxx>
Delivery-date:	Wed, 10 Nov 2010 00:50:44 -0800
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On 11/10/10 09:44, Jiang, Yunhong wrote:

-----Original Message-----
From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Juergen Gross
Sent: Wednesday, November 10, 2010 4:43 PM
To: Keir Fraser
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] How to detect HAP from DomU?

On 11/10/10 09:36, Keir Fraser wrote:

On 10/11/2010 08:22, "Juergen Gross"<juergen.gross@xxxxxxxxxxxxxx>   wrote:

is there any way for a HVM-domain to detect whether it is running with HAP
enabled? I couldn't find any interface for this information.

Background: in our BS2000 domain (HVM with PV-drivers) we sometimes have to
copy complete pages between kernel and user. An alternative to the copy
would be a remapping of the page. The remap is faster than the copy with HAP
enabled, but much slower without HAP. So it would be best to copy without HAP
and remap with HAP.


You could do a few remaps and copies and see how long it takes? Has the
advantage that you aren't tied up to one policy based on one system's
timings for those particuler ops. I don't think basing policy on static
assumptions about hidden implementation features is a good idea.


Okay, that's a good idea.
I'm going this way.


Will this works for Live Migration? After LM, your previous check will be 
invalid. (Can we migrate between system w/wo HAP?)
Or you can check after each LM.


The same problem applies to a decision based on information supplied by the
hypervisor.
I'll have to reconsider the decision in any case, dynamical testing just takes
some microseconds more, but is more flexible.


Juergen

--
Juergen Gross                 Principal Developer Operating Systems
TSP ES&S SWE OS6                       Telephone: +49 (0) 89 3222 2967
Fujitsu Technology Solutions              e-mail: juergen.gross@xxxxxxxxxxxxxx
Domagkstr. 28                           Internet: ts.fujitsu.com
D-80807 Muenchen                 Company details: ts.fujitsu.com/imprint.html

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Re: [Xen-devel] How to detect HAP from DomU?