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
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
> 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
> On Xen the packet are sent, and then receive
> Xen-devel mailing list
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