[Xen-bugs] [Bug 17] New: UDP packet loss in domU

[bugzilla-daemon@xxxxxxxxxxxxxxxxxxx]

http://bugzilla.xensource.com/cgi-bin/bugzilla/show_bug.cgi?id=17

           Summary: UDP packet loss in domU
           Product: Xen
           Version: 2.0
          Platform: x86
               URL: http://lists.xensource.com/archives/html/xen-devel/2005-
                    04/msg00783.html
        OS/Version: Linux
            Status: NEW
          Severity: major
          Priority: P1
         Component: Hypervisor
        AssignedTo: xen-bugs@xxxxxxxxxxxxxxxxxxx
        ReportedBy: rich@xxxxxxxxxxxxx


This appears to be a known problem, but it has serious operational implications.
    See description by Keir in cited link.

There are at least two use cases where this is a showstopper for use of Xen:

1) NFS over UDP: lost packets will lead to retries and/or hangs.
2) Syslog: lost packets = functional failure.

Note that on native Linux, the kernel will discard received UDP packets if an
application fails to receive them fast enougn.  Interrupt affinity can be used
to bind the network interrupt handler to a dedicated CPU, significantly
increasing (5-10X) the capacity of a UDP syslog server.

Scenario 1:

Once a UDP packet reaches the network device in dom0, it should never be lost
due to Xen-internal dynamics between dom0 and domU.  If the packet is not lost
on the wire, it should not be lost due to interaction between Xen and domU
kernels.  

Scenario 2:

domU - domU UDP throughput should be comparable to native - native UDP
throughput on GigE.

Filing this bug to collect use cases that will justify investigation, e.g.
develop a benchmark that will trigger repeatable worst-case behavior, which can
be used by developers for code optimization.



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