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[Xen-bugs] [Bug 691] New: iperf concurrently to dom0 & guest1 yields bad

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Subject: [Xen-bugs] [Bug 691] New: iperf concurrently to dom0 & guest1 yields bad net performance.
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Date: Tue, 27 Jun 2006 13:37:48 -0700
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           Summary: iperf concurrently to dom0 & guest1 yields bad net
           Product: Xen
           Version: unstable
          Platform: x86
        OS/Version: Linux-2.6
            Status: NEW
          Severity: major
          Priority: P2
         Component: Unspecified
        AssignedTo: xen-bugs@xxxxxxxxxxxxxxxxxxx
        ReportedBy: steve.tarver@xxxxxxxxxx

Test Setup: dom0 and xen1 are the root and guest domain on the xen machine and
are running iperf TCP servers. iperf clients are running on various machines. A
TCP test from any machine to either domains yields similar results. If I
connect two iperfs on the same machine to dom0 and xen1, dom0 gets twice the
bandwidth as xen1 but both are steady. If I connect machine A to dom0 and B to
xen1 and start the tests at nearly the same time, one domain gets all the
bandwidth and the other gets nearly nothing (perhaps some spikes to 10% or a
trickle). It seems that the first to start the test gets the bandwidth (doesn't
matter if it is dom0 or xen1). It doesn't matter which machine calls which
domain. Also, if I have A connected to dom0, wait a bit, and connect B to xen1,
B gets nothing until A finishes.

I have tried this enough different ways to think it should be trivial to
reproduce for anyone (with three computers). I would think this would be a big
enough, and obvious enough, problem to be noticed before - but...

Configuration: Clean FC5 install with xen 3.0.2-2 / vanilla kernel 2.6.16
downloaded from xensource about 6/14/2006. Guest OS is one created from the
xenguest-install.py in the FC5 distro (xen). All the setups are (pretty much)

Tools: get iperf at http://dast.nlanr.net/Projects/Iperf/ and a gui front end
jperf at http://dast.nlanr.net/projects/jperf/

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