WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

[Xen-devel] RE: Live migration fails due to c/s 20627

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] RE: Live migration fails due to c/s 20627
From: "Xu, Dongxiao" <dongxiao.xu@xxxxxxxxx>
Date: Wed, 16 Dec 2009 01:24:17 +0800
Accept-language: en-US
Acceptlanguage: en-US
Cc: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "kurt.hackel@xxxxxxxxxx" <kurt.hackel@xxxxxxxxxx>, "Dugger, Donald D" <donald.d.dugger@xxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, "Nakajima, Jun" <jun.nakajima@xxxxxxxxx>, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>
Delivery-date: Tue, 15 Dec 2009 09:25:56 -0800
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <4B27C360.7080906@xxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <6CADD16F56BC954D8E28F3836FA7ED7105AC8685A3@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx> <bcd71c68-8c44-40f7-a4f8-8e6102af2bee@default> <6CADD16F56BC954D8E28F3836FA7ED7105AC868872@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx> <4B27C360.7080906@xxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: Acp9qbwxwZNn3nzrTB2257IRsH6vHwAAHn/g
Thread-topic: Live migration fails due to c/s 20627
Jeremy Fitzhardinge wrote:
> On 12/15/09 08:10, Xu, Dongxiao wrote:
>>> Why not just add the code to do rdtscp emulation,
>>> which would NOT break live migration?
>>> 
>> Add rdtscp emulation has such problem that, in Intel VMX, the
>> vmexit control for rdtsc and rdtscp is the same, so if we trap
>> rdtscp for emulation, OS will suffer from looooots of rdtsc vmexit,
>> which will bring performance downgrade.
>> 
> 
> I don't see why that's relevant.  In the case where you've migrated
> the domain, if the CPU has rdtsc but not rdtscp, won't the rdtscp
> vmexit with an illegal instruction trap?  In that case you can
> emulate rdtscp while still having direct execution of rdtsc.

If CPU has rdtsc but no rdtscp, then the VM exec control bit in VMCS
won't be turned on. Therefore if rdtscp instruction runs, it will encounter
invalid op code directly but no VMEXIT.
> 
> Of course, having a wide difference between rdtscp and rdtsc
> performance may cause its own set of problems.
> 
>      J



Best Regards,
-- Dongxiao
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel