Re: [Xen-users] Xen 4.12 DomU hang / freeze / stall under high network/disk load

[Sarah Newman <srn@xxxxxxxxx>]

On 2/13/20 6:26 PM, Glen wrote:

> I tried both xl network-detach followed by a network-attach (feeding
> back in the parameters from my guest machine.)
OK. Were you able to check if the network device went away in the domU? It 
should have, but you won't see anything in dmesg necessarily.

> (XEN) Using scheduler: SMP Credit Scheduler rev2 (credit2)
> (XEN) Initializing Credit2 scheduler
This is something that changed by default from xen 4.11 to 4.12:

https://xenproject.org/2019/04/02/whats-new-in-xen-4-12/

You could try the old scheduler:

https://xenbits.xen.org/docs/unstable/features/sched_credit.html

I am skeptical this is the problem, but you could try the old one.

> > > maxmem=90112
> > > vcpus=26
> > This is fairly large.
> > Have you tried both fewer cpus and less memory? If you can reproduce with 
> > iperf, which probably will reproduce more quickly, can you reproduce with
> > memory=2048 and vcpus=1 or vcpus=2 for example? FYI the domU might not boot at 
> > all with vcpus=1 with some kernel versions.
> I... have not.... and please pardon my ignorance here, but my guest
> machine runs a lot of different things for our client, and definitely
> needs the RAM (and I *think* needs the CPUs, although I confess that
> I'm not sure how vcpus translate to available compute power.)  I can
> try the smaller numbers, but have not because to me it's off-point,
> since my guest requires the larger number of resources we've
> traditionally allocated.
Then set up another VM for testing?

Anything about your setup that's out of the ordinary is a reasonable place to start looking for problems. It may not solve your immediate issue but if 
it means a developer can reproduce, that gives you a chance of the bug actually getting fixed.
> So, going back to your "ideally by changing one thing at a time"
> comment, here's kind of how I'm proceeding:
I'd recommend you start by attempting to reproduce the problem as fast as possible, with the setup as-is, before changing anything. 4 days is too long 
to have any certainty.
BTW, if it's the domU network load - you would probably reproduce fastest by 
running testing between 2 domUs on the same dom0, if you can.

--Sarah

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