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] Strange network behaviour

To: Marco Tizzoni <marco.tizzoni@xxxxxxxxx>
Subject: Re: [Xen-devel] Strange network behaviour
From: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
Date: Tue, 28 Jul 2009 14:03:53 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
Delivery-date: Tue, 28 Jul 2009 06:04:17 -0700
Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:sender:received:in-reply-to :references:date:x-google-sender-auth:message-id:subject:from:to:cc :content-type:content-transfer-encoding; bh=Nc0iX4xZMZRdDKnbzTdhObuzBvRkHDqr7kZgz060LGM=; b=X+u5inDGWnKrEZ4X4uct3bYrRTeBJ5zgHWNx3agIW1fjrlyYXIR4r3x4rgsouSq5Eq y2d+cprh6RxPm0gNeJYAOy3TP7iJkKOTJ15kz0l4e1qBSjwn3x7DGUJ8dVY1Qb4WyrSZ dh8Tnh0PPAwYPavO0BYyBICFtwSGwu2fkZ7R0=
Domainkey-signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type :content-transfer-encoding; b=wFyR6OFMedYxqoWdU1r9klQt11VqZhsCyveLeYOPN13deptV3sTac+Nlf1L7oY9Upq HXdRDa4Q8aM7o6KtoY/wCrDcy5e8rq0/B+TsIhmit2uw4qly4rCkeNKRfTBg2OaTe7ZT WKkQro4YnjKee1Z2WcssihxSAHXpzJlA3KDHA=
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <f9611b0f0907280121r271078fci35ed52d0ff955d9@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/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: <f9611b0f0907280121r271078fci35ed52d0ff955d9@xxxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
What's the granularity of your measurement?

If, for example, the actual delta between was 1.5ms, but you're only
measuring at a 1ms granularity, you'd expect to see something like

Actual time, measured time
1 , 1
2.5, 3
4 , 4
5.5 , 6
7 , 7



On Tue, Jul 28, 2009 at 9:21 AM, Marco Tizzoni<marco.tizzoni@xxxxxxxxx> wrote:
> Hi guys,
> I'm doing some tests to understand how credit and sedf schedulers
> perform on real-time systems in mixed io and cpu intesive
> environments.
> During my first test I saw a quite strange behaviour I'm going to describe.
> The test has been setup as follow: 1 domain running Linux with default
> scheduler setup and one bridged network. Here iperf run as a client
> and sends udp packet to an host on the same net with 1Mb/s rate. Dom0
> runs nothing except XenMon. Iperf (server mode) and a tcpdump run on a
> non-virtualized host.
> Measuring packets inter occurences, I'd expect to find out a costant
> value because of the constant rate at which the packet are sent. It's
> not so.
> Let say the first packet arrives after 1ms, the second arrives after
> 3, the third after 4, the fourth after 6 and so on. The interoccurence
> times are:
> Packet#         Absolute Time        Interoccurence Time
>  1                           1                            1
>  2                           3                            2
>  3                           4                            1
>  4                           6                            2
>  5                           7                            1
>  6                           9                            2
> ...                          ....
> I tried to shutdown domU and run iperf on dom0, same result.
> The last test I made was run iperf on a non-virtualized environment.
> And here I got the results I expect: constant interoccurence time.
> Do  you have any idea of the reasong why the packet are sent with this
> strange rate even if there are no other domains competiting for
> resources?
> Thaks,
> Marco
> On Xen the packet are sent, and then receive
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel

Xen-devel mailing list

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