Bug 431898 - Xen network performance are almost zero
Xen network performance are almost zero
Product: Red Hat Enterprise Linux 5
Classification: Red Hat
Component: xen (Show other bugs)
All Linux
low Severity high
: rc
: ---
Assigned To: Xen Maintainance List
Virtualization Bugs
Depends On:
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Reported: 2008-02-07 13:16 EST by Paolo Campegiani
Modified: 2009-12-14 16:25 EST (History)
0 users

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Fixed In Version:
Doc Type: Bug Fix
Doc Text:
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Clone Of:
Last Closed: 2008-02-23 10:14:04 EST
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RHEL 7.3 requirements from Atomic Host:
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Description Paolo Campegiani 2008-02-07 13:16:47 EST
Description of problem:

bare machine: HP DL 380 G5 with two Broadcom NIC, updated to the last firmware
revision as found on the HP support web site
virtual machine: two RHEL 5.0 with hardware assisted virtualization
on the first domU, there's a netperf server listening
on the second domU, it's started the tcp_stream_script

Results: bandwidth of 2.5 Mbps, and the domU with the netperf server is
reporting dropped packets and errors on eth0. Dom0 reports no errors.

Things tried to do with no success:

- ifconfig eth0 mtu 1400 on both domU
- net.ipv4.tcp_{r,w}mem = 4096 1398080 8388608 
- net.core.{w,r}mem_max = 8388608                both on domO
- txqueuelen set to 3000 for virbr0,xenbr0,vif,etc

Note that "normal" networking works, the problem arises only with tcp-intensive
workload (the original problem was triggered by MPI benchmark showing poor
results. i.e. 2 MFlops sustained for 2 virtual machines, whilst 1 virtual
machine shows about 800 MFlops)

kernel on virtual machines: 2.6.18-8.1.3.el5
kernel on physical machine: 2.6.18-53.1.4.el5xen

on xen ml this problem has hit some peoples (everyone using broadcom NICs, but
as they are widely adopted could be unrelated to the real problem), with no
working solutions (except: using XenExpress). It seems it could be related to
missing PV drivers. On both virtual machines it's aliasing eth0 with 8139cp
Comment 1 Paolo Campegiani 2008-02-14 03:26:33 EST
-Updated the dom0 with kernel 2.6.18-53.1.13.el5xen
- the firmware of the Broadcom BCM5708 is 1.9.6
- disabled the management function as described in

now performances are about 45 Mbps from domU to domU in the same domO, the domU
with netserver has lots of dropped packets and errors, other domU and domO have
no errors. 
Comment 2 Paolo Campegiani 2008-02-23 06:08:30 EST
After using the paravirtualized drivers, as described here:


netperf shows a 347 MBps (2912*10^6 bits per second) sustained throughput for a

please close.

Comment 3 Daniel Berrange 2008-02-23 10:14:04 EST
Closing ticket, at request of reporter.

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