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] [PATCH] per-cpu timer changes

To: "Don Fry" <brazilnut@xxxxxxxxxx>, <Xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH] per-cpu timer changes
From: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>
Date: Tue, 24 May 2005 02:20:36 +0100
Delivery-date: Tue, 24 May 2005 01:20:00 +0000
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
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>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AcVf+J+EJOz9VzpmQOmffaVUFdqUmwAAyRPA
Thread-topic: [Xen-devel] [PATCH] per-cpu timer changes
> Here are some patches to help xen run on a system where the 
> CPUs are not synchronized so that the tsc counters drift.  
> Without this patch I get lots of 'time went backwards' 
> messages in the linux logs.  I still get an occasional 
> message, but not the number I did previously.

Don,

This is looking good. To help other people review the patch, it might be
a good idea to post some of the design discussion we had off list as I
think the approach will be new to most people. (Perhaps put some of the
text in a comment in the hypervisor interface).

As regards the time going backwards messages, if you're seeing small -ve
deltas, I'm not surprised -- you need to round to some precision as we
won't be nanosecond accurate. Experience suggests we'll be good for a
few 10's of ns with any kind of decent crystal. We could round to e.g.
512ns or 1024ns to make sure.

Best,
Ian

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