[Qemu-devel] 8139cp problems - steps to reproduce

[Nikola Ciprich]

Hello Avi and everybody,

(and in advance, sorry for cross-posting).

As it was already reported, some people (including me :)) have problems
with network getting stuck from time to time in KVM guests. 

According to 
http://qemu-forum.ipi.fi/viewtopic.php?f=4&t=4563&start=0&st=0&sk=t&sd=a&sid=fcf252234991e017919ca7d0eb3799a3
the problem is maybe not KVM speciffic.

I can confirm that the problem seems to be occuring after transmitting few 
gigabytes of data,
so it can be simply reproduced by starting KVM guest, mounting some NFS in it, 
and then
starting shell loop dd if=/mnt/nfs/bigimage.iso of=/dev/zero
after some runs (in my case usually tens of GB), the problem occurs:
[ 2159.614496] NETDEV WATCHDOG: eth0: transmit timed out
[ 2159.614537] eth0: Transmit timeout, status  d   2b   15 80ff

The status "  d   2b   15 80ff" is always the same, on all testing machines
which according to 8139cp.c means

Command register=d
C+ command register=2b
Interrupt status=15
Interrupt mask=80ff

Particular bits are explained in 8139cp comments, unfortunately this didn't 
make me any smarter :(. 
The only thing I tried was disabling rx/tx checksumming for the interface (this 
was needed
fox XEN domUs as well), but it didn't helped.

What is important to note is, that this is simply reproducible this way for 
x86_32 guests (I'm
using x86_64 host). For x86_64 guests, the problem is actually much WORSE, as 
it usually gets
host machine into totally unusable state (it replies to pings, but that's all, 
no message in logs
after reboot, etc). I'll try to investigate it further.

Another important note is, that the problem is certainly NOT system-load 
related, it
occurs even when the machine is idle (except from load caused by network dd)

I'm using kvm-74 now, with 2.6.26 host and 2.6.24 guest, and bridged networking.

I'll try using e1000 driver, but I think that 8139cp is ATM considered the most 
stable choice, right?

So does somebody have an idea on where the problem could be? Of course I'll be 
glad to (try) to help
debugging...

Thanks a lot in advance!

nik


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Nikola CIPRICH
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