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

[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"

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



# xl info -n
release                : 3.13.0-141-generic
version                : #190-Ubuntu SMP Fri Jan 19 12:52:38 UTC 2018
machine                : x86_64
nr_cpus                : 16
max_cpu_id             : 31
nr_nodes               : 2
cores_per_socket       : 4
threads_per_core       : 2
cpu_mhz                : 2533
hw_caps                :
bfebfbff:28100800:00000000:00003b00:009ce3bd:00000000:00000001:00000000
virt_caps              : hvm hvm_directio
total_memory           : 122869
free_memory            : 104431
sharing_freed_memory   : 0
sharing_used_memory    : 0
outstanding_claims     : 0
free_cpus              : 0
cpu_topology           :
cpu:    core    socket     node
  0:       0        0        0
  1:       0        0        0
  2:       1        0        0
  3:       1        0        0
  4:       2        0        0
  5:       2        0        0
  6:       3        0        0
  7:       3        0        0
  8:       0        1        1
  9:       0        1        1
 10:       1        1        1
 11:       1        1        1
 12:       2        1        1
 13:       2        1        1
 14:       3        1        1
 15:       3        1        1
numa_info              :
node:    memsize    memfree    distances
   0:     61952      56439      10,20
   1:     61439      47992      20,10
xen_major              : 4
xen_minor              : 4
xen_extra              : .2
xen_version            : 4.4.2
xen_caps               : xen-3.0-x86_64 xen-3.0-x86_32p hvm-3.0-x86_32
hvm-3.0-x86_32p hvm-3.0-x86_64
xen_scheduler          : credit
xen_pagesize           : 4096
platform_params        : virt_start=0xffff800000000000
xen_changeset          :
xen_commandline        : placeholder dom0_mem=1024M,max:1024M
dom0_max_vcpus=4 dom0_vcpus_pin iommu=no-intremap
cc_compiler            : gcc (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4
cc_compile_by          : stefan.bader
cc_compile_domain      : canonical.com
cc_compile_date        : Fri Oct 13 15:48:48 UTC 2017
xend_config_format     : 4

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