Thanks for finding and checking the problem.
I will try to reproduce the issue and check what caused the problem.
Jeremy Fitzhardinge wrote:
> On 08/22/2010 09:43 AM, Christophe Saout wrote:
>> I've been playing with some of the new pvops code, namely DomU guest
>> code. What I've been observing on one of the virtual machines is
>> the network (vif) is dying after about ten to sixty minutes of
>> The unfortunate thing here is that I can only repoduce it on a
>> production VM and have been unlucky so far to trigger the bug on a
>> test machine. While this has not been tragic - rebooting fixed the
>> issue, unfortunately I can't spend very much time on debugging after
>> the issue pops up.
> Ah, OK. I've seen this a couple of times as well. And it just
> happened to me then...
>> Now, what is happening is that the receive path goes dead. The DomU
>> can send packets to Dom0 and those are visible using tcpdump on the
>> Dom0 on the virtual interface, but not the other way around.
> I hadn't got to that level of diagnosis, but I can confirm that
> that's what seems to be happening here too.
>> Now, I have done more than one change at a time (I'd like to avoid
>> going into pinning it down since I can only reproduce it on a
>> production machine, as I said, so suggestions are welcome), but my
>> suspicion is that it might have to do with the new "smart polling"
>> feature in xen/netfront. Note that I have also updated Dom0 to pull
>> in the latest dom0/backend and netback changes, just to make sure
>> not due to an issue that has been fixed there, but I'm still seeing
>> the same.
> I agree. I think I started seeing this once I merged smartpoll into
>> The production machine is a machine that doesn't have much network
>> load, but deals with a lot of small network requests (DNS and smtp
>> mostly). A workload which is hard to reproduce on the test machine.
>> Heavy network load (NFS, FTP and so on) for days hasn't triggered the
>> problem. Also, segmentation offloading and similar settings don't
>> have any effect.
>> The machine has 2 physical and the VM 2 virtual CPUs, DomU has
>> I've been looking at the code, if there might be a race condition
>> somewhere, something like where one could run into a situation where
>> the hrtimer doesn't run and Dom0 believes the DomU should be polling
>> and doesn't emit an interrupt or something, but I'm afraid I don't
>> know enough to judge this (I mean, there are spinlocks which look
>> to me).
>> Do you have any suggestions what to try? I can trigger the issue on
>> the production VM again, but debugging should not take more than a
>> minutes if it happens. Access is only possible via the console.
>> Neither Dom0 nor the guest show anything unusual in the kernel
>> and continue to behave normally after the network goes dead (also
>> to shut down the guest normally).
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