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Re: [Xen-users] Vif dropping packets

Basically i wanted to know if any resource consyraints exist.

Do packet drops occur all the time?

1. What about with a steady state load?
2. What about no load?
3. What about a heavy load?

There's an IBM study that shows xen systems with more than 12vms AND CPU overcommitnent can have unusual delays responding to requests.
I've seen similar behavior but only  on a busy host with busy vms.

I think that you need more data.

On Jun 26, 2009, at 6:26 PM, Mike Lovell <mike@xxxxxxxxxxxx> wrote:

I'm not entirely sure what you are asking with that second question. sar is installed in the guests. I did `sar -u1 1000` to watch the status for a while. Here is an abbreviated output with the averages and the line I saw with the highest %steal

04:13:12 PM CPU %user %nice %system %iowait %steal %idle 04:13:16 PM all 0.00 0.00 0.00 0.00 0.99 99.01 Average: all 0.01 0.00 0.02 0.55 0.05 99.37

Overall, these vms aren't doing a lot. Mainly sitting idle waiting for a QA engineer to test code functionality. I should probably say a little more about the config. The host boxes are dual quad-core Opteron 2346HE systems with 24GB of memory and a ton of disks. Currently there are 28 virtual machines running on the one I have been checking but most of them idle.

Hope that helps or is what you were looking for.


Peter Booth wrote:

You don't say anything about the workload on your system or the resource consumption that it causes.

Do you have sar installed on the domUs? Does a one second vmstat show a %st that's above 1%?

Sent from my iPhone

On Jun 26, 2009, at 4:22 PM, Mike Lovell <mike@xxxxxxxxxxxx> wrote:

I have a problem with packets being dropped on some vif interfaces. I currently have a box running Debian Lenny with Xen 3.2.1. The host is running the Xen-ified kernel from the Debian repos. 2.6.26-1-xen-amd64. The host has a single bridge, 'vmnet', that connects to one physical interface and all of the guest's interfaces connect to. If I do a 'ifconfig vifX.0', I see dropped TX packets. Looking at the guest does not show any dropped packets on its interface.

From the host
# cat /etc/network/interfaces
auto vmnet
iface vmnet inet static
     bridge_ports eth1
     bridge_stp off
     bridge_fd 9
     bridge_hello 2
     bridge_maxage 12

# brctl show vmnet
bridge name    bridge id        STP enabled    interfaces
vmnet               8000.003048c8166d    no        eth1
vif22.0 ... <lots of interfaces>

# ifconfig vif22.0
vif22.0 Link encap:Ethernet HWaddr fe:ff:ff:ff:ff:ff inet6 addr: fe80::fcff:ffff:feff:ffff/64 Scope:Link
       RX packets:7946252 errors:0 dropped:0 overruns:0 frame:0
       TX packets:8282858 errors:0 dropped:160 overruns:0 carrier:0
       collisions:0 txqueuelen:32
       RX bytes:5758663699 (5.3 GiB)  TX bytes:5887860418 (5.4 GiB)

From the guest
# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:16:3E:02:00:91 inet addr: Bcast: Mask:
       inet6 addr: fe80::216:3eff:fe02:91/64 Scope:Link
       RX packets:8283072 errors:0 dropped:0 overruns:0 frame:0
       TX packets:7946364 errors:0 dropped:0 overruns:0 carrier:0
       collisions:0 txqueuelen:1000
       RX bytes:5887884877 (5.4 GiB)  TX bytes:5869927068 (5.4 GiB)

# cat /etc/network/interfaces

auto eth0
iface eth0 inet dhcp
post-up ethtool -K eth0 tx off

I am a stumped on this and it is causing some problems for some of the applications that are being tested across the virtual machines. For example, one app on one vm needs to connect to a database, on another vm, but it can't and complains. Do any of you know what might be causing this or any ways to fix this? Thanks in advance.


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