[Xen-users] vif interfaces drop packets

[Torsten Vielhak <Torsten@xxxxxxxxxx>]

Hi all,

I have 2 virtual machines running and everything runs just fine except
that I have some
network issues. Both machines are in the same ip network and are
attached to the same
bridging interface:
# brctl show
bridge name     bridge id               STP enabled     interfaces
xen-br0         8000.0013216b6112       no              eth1
                                                        vif1.0
                                                        vif2.0

If I look at the ifconfig stats I see TX packet drops on the vif interfaces:
eth1      Link encap:Ethernet  HWaddr 00:13:21:6B:61:12
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2900161 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1437145 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:215418139 (205.4 MiB)  TX bytes:106086424 (101.1 MiB)
          Interrupt:26

vif1.0    Link encap:Ethernet  HWaddr FE:FF:FF:FF:FF:FF
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:5585927 errors:0 dropped:0 overruns:0 frame:0
          TX packets:5649573 errors:0 dropped:13923 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:1385954050 (1.2 GiB)  TX bytes:2747246776 (2.5 GiB)

vif2.0    Link encap:Ethernet  HWaddr FE:FF:FF:FF:FF:FF
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:4932512 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6466388 errors:0 dropped:9191 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:2700280469 (2.5 GiB)  TX bytes:1447794114 (1.3 GiB)

xen-br0   Link encap:Ethernet  HWaddr 00:13:21:6B:61:12
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:154640 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:14863871 (14.1 MiB)  TX bytes:0 (0.0 b)

Could someone explain these packet drops? The packet drops occur mostly
under
higher load (CPU and/or network) and can be reproduced by communicating
between
the two virtual machines (over the bridge without involving the "real"
network) but
also if I try to connect from the outside to the virtual machine I have
packet loss.
I noticed the lines
/* Disable queuing. */
dev->tx_queue_len = 0;
in interface.c (netback source of XEN). Could this lead into problems if
the bridge
does not react fast enough to receive packets from the vifs in high load
situations?

cheers,
    Torsten


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