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

RE: [xen-devel] System time monotonicity

To: <dan.magenheimer@xxxxxxxxxx>, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [xen-devel] System time monotonicity
From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date: Wed, 9 Apr 2008 11:20:09 +0800
Delivery-date: Tue, 08 Apr 2008 23:38:47 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <20080408195504234.00000004064@djm-pc>
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/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <D470B4E54465E3469E2ABBC5AFAC390F024D9192@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> <20080408195504234.00000004064@djm-pc>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AciZl4WQxEBTGAWKEd2fxQAWy6hiGQABBvOAABCRjTAAAOXDcAAC4wPw
Thread-topic: [xen-devel] System time monotonicity
>From: Dan Magenheimer [mailto:dan.magenheimer@xxxxxxxxxx] 
>Sent: 2008年4月9日 9:55
>
>> Or you have to configure HVM guest to not trust TSC...
>
>Yes, that's what I'm thinking... like Linux, Xen could/should
>build virtual platform timers on a physical clocksource other
>than tsc if all of the potential vcpu->pcpu mappings are not
>on sync'd-TSC-pcpus.

virtual platform timers are only one area. The most important is
TSC itself which is used frequently by guest to calculate relative
offset...

>
>I assume this problem is worse with multi-socket Hypertransport
>and future Intel QPI boxes?  Or is TSC (and frequency changing)
>synchronized for such systems?

For same crystal case, Intel processors with VT-x support all have 
TSC constant feature which is not bound to frequency change and 
can be detected by CPUID. But for multiple crystals case, Xen may
need tackle affinity then.

Thanks,
Kevin

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