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Hi Klaus

Op wo 8 mei 2019 om 11:52 schreef Klaus Darilion <klaus.mailinglists@xxxxxxxxx>:

Hello!

Ubuntu 14.04, 3.13.0-141-generic #190-Ubuntu SMP Fri Jan 19 12:52:38 UTC
2018 x86_64, xen_version: 4.4.2, Server: DL380 G6 with 2x Intel E5540
(more details below)

We configured our dom0 with a single CPU:
GRUB_CMDLINE_XEN="dom0_mem=1024M,max:1024M dom0_max_vcpus=1
dom0_vcpus_pin iommu=no-intremap"

If the load on your server is also network related then the Dom0 needs memory to handle network sessions. Maybe increasing the dom0_mem to 2048M would help prevent crashes. Two cpus instead of only 1 cpu will also help since the Dom0 must handle IO for the DomU hosts.

In addition you could also give the Domain-0 more prio for IO, so it will not compete with DomU hosts in cpu cylces.

You can do that by increasing the sched-credits to 512 (max value) for the Domain-0

xl sched-credit -d Domain-0 -w 512

This helped us a lot to improve overall responsiveness. The Dom0 needs to do the real work in the end, so if it can complete its work a.s.a.p. it is best for the performance of the DomU.

The last 5 years we did not had any single problem with Xen. Yesterday,
we had poor io-performance when using dd in the dom0 and tried if it
would be better when having more CPUs. Hence, we changed dom0_max_vcpus
to 4 vCPUs. io was much better, but today it crashed (the server was
totally unresponive, we had to power toggle it, hence, no console logs).

We saw that more than once (Ubuntu 14.04 on DL380G6 with dual CPU,
Debian 9 on DL380G7 with single CPU) that Xen locks up when we tried to
play with the number of CPUs in the dom0, or with CPU pinning.

Is there a known issue with this Xen version, this hardware, or whatever
which can cause this Xen lock ups when using multiple vCPUs?

What is the recommended setting for number of CPUs in the dom0?

Thanks
Klaus

Greetings,

Roalt

Re: [Xen-users] dom0 crashes when having more than 1 vCPU