Raphael Hertzog
2009-Jun-08 21:46 UTC
[Xen-devel] Constantly varying download rate with a complex xen networking setup, why?
[ Please CC me I''m not subscribed ]
Hello,
I have a weird problem and I''m not sure if it comes from linux or from
Xen. Thus I''d like your opinion and maybe your help so that I can
do a proper bugreport where it belongs.
(Note the full description below has also been submitted to
http://serverfault.com/questions/22219/)
The network configuration in my Xen setup:
- the dom0 has 3 network cards (eth0, eth1, eth2), 3 brigdes (xenbrE,
xenbrI, xenbrD) and each brigde integrates the corresponding network
card. Only xenbrD has an IP address configured (192.168.78.2, a private
LAN) so that it can discuss with all domU.
- there''s a domU that is a firewall/router and it also contains 3
virtual
cards (eth0, eth1, eth2). It does masquerading for traffic going out on
eth0 (the external interface which is part of xenbrE).
# grep vif /etc/xen/xm.slis
vif = [ ''mac=00:16:3e:14:85:11, bridge=xenbrE'',
''mac=00:16:3e:14:85:12, bridge=xenbrI'',
''mac=00:16:3e:14:85:13, bridge=xenbrD'' ]
My problem is that when I download a big file from the internet by HTTP in
the dom0, the download rate is not stable. It goes up progressively and then
stalls for a few seconds, and restart again going up progressively (and
all this in loop until the download is complete). During the stalls, it looks
all networking is blocked on the machine (noticed on interactive SSH sessions).
dom0 │domU
wget │
↕ │
eth2↔xenbrD(192.168.78.2)↔vif2.2←┼→eth2(192.168.78.1/24)
│ ↕ masquerading
eth0↔xenbrE↔vif2.0←——————————————┼→eth0(192.168.1.20/24)
↕
internet
If I do the same download but uses a (non-caching) HTTP proxy that runs in
the firewall domU, the download rate is stable at its maximum value.
How can I avoid this problem?
I suspect it''s a bug in the networking stack but I would like
assistance
to diagnose it more precisely (and maybe find a work-around).
This is a Debian Etch system with Xen 3.2 and the 2.6.26-xen-686 kernel of
Debian Lenny (backports). The bridges are created with
/etc/network/interfaces:
auto lo
iface lo inet loopback
auto xenbrE
iface xenbrE inet manual
bridge_ports eth0
bridge_maxwait 0
auto xenbrI
iface xenbrI inet manual
bridge_ports eth1
bridge_maxwait 0
auto xenbrD
iface xenbrD inet static
address 192.168.78.2
netmask 255.255.255.0
gateway 192.168.78.1
bridge_ports eth2
bridge_maxwait 0
The xend configuration is not complicated:
# grep ''^('' /etc/xen/xend-config.sxp
(network-script network-dummy)
(vif-script vif-bridge)
(dom0-min-mem 150)
(dom0-cpus 0)
(vncpasswd '''')
And the only routing in dom0 redirects to the domU via xenbrD:
# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use
Iface
192.168.78.0 0.0.0.0 255.255.255.0 U 0 0 0
xenbrD
0.0.0.0 192.168.78.1 0.0.0.0 UG 0 0 0
xenbrD
In the domU, the only iptables configuration done is `iptables -t nat -A
POSTROUTING -s 192.168.78.0/24 -o eth0 -j MASQUERADE`.
Thank you for your help.
--
Raphaël Hertzog -+- http://www.ouaza.com
Freexian : des développeurs Debian au service des entreprises
http://www.freexian.com
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel
Raphael Hertzog
2009-Jun-10 14:16 UTC
[Xen-devel] Constantly varying download rate with a complex xen networking setup, why?
[ Please CC me ]
Hello,
I have a weird problem and I''m not sure if it comes from linux or from
Xen. Thus I''d like your opinion and maybe your help so that I can
do a proper bugreport where it belongs. I can do supplementary tests on
request of course.
(Note the full description below has also been submitted to
http://serverfault.com/questions/22219/)
The network configuration in my Xen setup:
- the dom0 has 3 network cards (eth0, eth1, eth2), 3 brigdes (xenbrE,
xenbrI, xenbrD) and each brigde integrates the corresponding network
card. Only xenbrD has an IP address configured (192.168.78.2, a private
LAN) so that it can discuss with all domU.
- there''s a domU that is a firewall/router and it also contains 3
virtual
cards (eth0, eth1, eth2). It does masquerading for traffic going out on
eth0 (the external interface which is part of xenbrE).
# grep vif /etc/xen/xm.slis
vif = [ ''mac=00:16:3e:14:85:11, bridge=xenbrE'',
''mac=00:16:3e:14:85:12, bridge=xenbrI'',
''mac=00:16:3e:14:85:13, bridge=xenbrD'' ]
My problem is that when I download a big file from the internet by HTTP in
the dom0, the download rate is not stable. It goes up progressively and then
stalls for a few seconds, and restart again going up progressively (and
all this in loop until the download is complete). During the stalls, it looks
all networking is blocked on the machine (noticed on interactive SSH sessions).
dom0 │domU
wget │
↕ │
eth2↔xenbrD(192.168.78.2)↔vif2.2←┼→eth2(192.168.78.1/24)
│ ↕ masquerading
eth0↔xenbrE↔vif2.0←——————————————┼→eth0(192.168.1.20/24)
↕
internet
If I do the same download but uses a (non-caching) HTTP proxy that runs in
the firewall domU, the download rate is stable at its maximum value.
How can I avoid this problem?
I suspect it''s a bug in the networking stack but I would like
assistance
to diagnose it more precisely (and maybe find a work-around).
This is a Debian Etch system with Xen 3.2 and the 2.6.26-xen-686 kernel of
Debian Lenny (backports). The bridges are created with
/etc/network/interfaces:
auto lo
iface lo inet loopback
auto xenbrE
iface xenbrE inet manual
bridge_ports eth0
bridge_maxwait 0
auto xenbrI
iface xenbrI inet manual
bridge_ports eth1
bridge_maxwait 0
auto xenbrD
iface xenbrD inet static
address 192.168.78.2
netmask 255.255.255.0
gateway 192.168.78.1
bridge_ports eth2
bridge_maxwait 0
The xend configuration is not complicated:
# grep ''^('' /etc/xen/xend-config.sxp
(network-script network-dummy)
(vif-script vif-bridge)
(dom0-min-mem 150)
(dom0-cpus 0)
(vncpasswd '''')
And the only routing in dom0 redirects to the domU via xenbrD:
# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use
Iface
192.168.78.0 0.0.0.0 255.255.255.0 U 0 0 0
xenbrD
0.0.0.0 192.168.78.1 0.0.0.0 UG 0 0 0
xenbrD
In the domU, the only iptables configuration done is `iptables -t nat -A
POSTROUTING -s 192.168.78.0/24 -o eth0 -j MASQUERADE`.
Thank you for your help.
--
Raphaël Hertzog -+- http://www.ouaza.com
Freexian : des développeurs Debian au service des entreprises
http://www.freexian.com
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel