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[Xen-users] Problem of slowness network when Nash is killed

(sorry for my english)
I have a strange problem :

I use for my dom0 the kernel of dom0
On my DomU (all is redhat 4.3), Process nash-hotplug take 99% CPU.
I have already see in mail archives that i can kill this process.
Indeed, is a good soluce, but It have big consequence : Network become very slow !

In an other machine on network, i use a ping flood and i look performance.
When nash is running, i observe 200-300 ko/s.
If i kill nash (or just STOP it with a kill -STOP), i have 40-50 ko/s maximum (if i restart nash with kill -CONT, i have again 300ko/s !)

I try to make a new initrd in domU : i don't have nash any more, but network is slow every time.

I notice that if i use vcpus > 1 in domU, network is slow every time.
with vpcus=1 and nash running : all is ok (except cpu load)

I have 2 others servers, exactly the same, but without several bridge (just one), upgrade ok for centos 5, and network stay quick when i kill nash: it is a coincidence, or a bug is already fixed ?

DomU : redhat 4.3, 64bit
ex :
kernel = '/boot/vmlinuz-2.6.18-8.1.4.el5xen'
ramdisk = '/boot/initrd-2.6.18-8.1.4.el5xen-domU.img'
memory  = '750'
root ='LABEL=xenpiraatsda1'
disk    = ['phy:/dev/rootvg/xen_piraat_sda1,sda1,w']
cpus = "1-3"
vcpus   = 1
#  Hostname
name    = 'piraat'
#  Networking
dhcp = 'dhcp'
vif  = [  'mac=00:16:3E:2F:18:F7, bridge=xenbr0' ]
#  Behaviour

on_reboot   = 'restart'
on_crash    = 'restart'

Dom0 :
CentOS release 5 (Final) 64bit, 16Go de RAM
Linux helicon 2.6.18-8.1.4.el5xen #1 SMP Thu May 17 03:43:13 EDT 2007 x86_64 x86_64 x86_64 GNU/Linux

2 bridges for network (1 per vlan) :
# !/bin/sh
# network-xen-multi-bridge
# Exit if anything goes wrong
set -e
# First arg is operation.
case ${OP} in
$script start vifnum=1 bridge=xenbr1 netdev=eth1
$script start vifnum=0 bridge=xenbr0 netdev=eth0
$script stop vifnum=1 bridge=xenbr1 netdev=eth1
$script stop vifnum=0 bridge=xenbr0 netdev=eth0
$script status vifnum=1 bridge=xenbr1 netdev=eth1
$script status vifnum=0 bridge=xenbr0 netdev=eth0
echo 'Unknown command: ' ${OP}
echo 'Valid commands are: start, stop, status'
exit 1

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