[ kvm-Bugs-2506814 ] TAP network lockup after some traffic

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2009-01-14T13:24:47Z

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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Fabio Coatti (cova)
Assigned to: Nobody/Anonymous (nobody)
Summary: TAP network lockup after some traffic

Initial Comment:
Hi all,
we are experiencing severe network troubles using kvm+tap networking.
basically, after some network load (we have yet to identify the exact amount of traffic if one exist) network stops working.
During lockups, With tcpdump we can see arp requests on guest interface, then on tap, brX and physical interfaces on host system.
the arp answers can be seen, with tcpdump, only on physical host interface and bridge (brX), but not on tap device. Basically it seems that packets coming from external network get lost in tap device on the way to guest (kvm). Looking at tap data with ifconfig, the only weird thing is the TX packets overrun count that is > 0. every time the network stops working, overrun count increases.
This has been observed with several kvm releases (for sure, 76/77/78/79/80/81/82) and with different kernels (tried with some versions among 2.6.25.X, 26.X, 27.X, 28) both on guest and host side.
we tried several network drivers (virtio, e1000, rtl) and all shows the same problem. Only 100Mbit drivers seems to be unaffected so far. (only virtio has acceptable performance)
(btw: on host machine we have vlan on top of ethX devices)
cpu number on guest makes no difference.
we tried with vanilla kernel provided kvm modules and with kvm package provided modules.
guest: 32 bit
host: 64 bit
host machine:

2 x Quad-Core AMD Opteron(tm) Processor 2352 16GB, gentoo.

Of course I can provide more details or perform other tests and try patches, if someone can give me some hints and advices they will be most welcome.

Thanks.

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>Comment By: Fabio Coatti (cova)