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/
Home Products Support Community News


Re: [Xen-devel] system time skew measurement patch

To: "dan.magenheimer@xxxxxxxxxx" <dan.magenheimer@xxxxxxxxxx>, "Xen-Devel (E-mail)" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] system time skew measurement patch
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Mon, 21 Apr 2008 23:52:28 +0100
Delivery-date: Mon, 21 Apr 2008 15:53:07 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <20080421150000078.00000007176@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>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: Acij8qfr3eN+Hq6zQZSPY+jdn0NuoAAD7eho
Thread-topic: [Xen-devel] system time skew measurement patch
User-agent: Microsoft-Entourage/

On 21/4/08 22:00, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

> The patch below printk's useful interprocessor system time skew
> information.  Patch is relative to xen-unstable.  Printk is
> rate-limited to output only when O(max skew) grows.  Max skew
> is measured across all cores/processors... ideally eventually it
> should be measured for each processor and exported via "xm info"
> so groups of sync'ed processors can be properly identified.
> Even on my Core 2 Duo E6850 @ 3.00 GHz (1 socket), I am seeing
> skew on the order of 6000 cycles (2 usec).  I'm not clear on
> whether this is due to the calibration algorithm or the
> hardware.

This is not unexpected. Stick a max() function at the end of get_s_time()
and we'll be fine.

 -- Keir

Xen-devel mailing list

<Prev in Thread] Current Thread [Next in Thread>