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] reading time value in dom0 and domU kernels

To: "sanjay kumar" <sanjay.kushwaha@xxxxxxxxx>
Subject: Re: [Xen-devel] reading time value in dom0 and domU kernels
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Sun, 9 Apr 2006 16:56:20 +0100
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
Delivery-date: Sun, 09 Apr 2006 08:59:45 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <2717599f0604090819g5433b228p486ae4f8dbb343e9@xxxxxxxxxxxxxx>
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: <2717599f0604090819g5433b228p486ae4f8dbb343e9@xxxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx

On 9 Apr 2006, at 16:19, sanjay kumar wrote:

Hi Folks,
I want to calculate latency in transferring a buffer from domU kernel to dom0 kernel and vice versa. for that I need a time 'flavour' (cycle counter time?) which reads the same in dom0 and domU. Could someone please let me know if cycle counter time is the right time to use? if not then which one (system time or wall clock time)? Also could someone please tell me how to read to read this timer value.

if I use rdtsc() in both dom0 and domU, will it give me the same time value?

It should be close enough as Xen attempts to synchronise the TSCs of all CPUs during boot and on most x86 platforms the TSCs will not diverge.

If you're measuring in the kernel then something like 'sched_clock()' will get you system time in nanoseconds. That would be slightly preferable as system time is actively synchronised across all domains. With TSC you are winging it a tiny bit (although it's usually an okay strategy on x86).

 -- Keir

Xen-devel mailing list

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