Hi all,

I know that XenSource allows us to configure how much memory and how many
vcpus are available to the Domain0 through kernel boot parameters (dom0_mem
and dom0_max_vcpus). XCP is underlying using XenSource, then these settings
should also work with XCP.

I'm trying to specify these boot parameters in the /boot/extlinux.conf file
of my Domain0 VMs (Control Domains):

# /boot/exlinux.conf
# ...
label xe
  # XenServer
  append /boot/xen.gz dom0_max_vcpus=4 dom0_mem=752M
lowmem_emergency_pool=16M crashkernel=...@32m ...


The dom0_mem works just fine. My problem is with the dom0_max_vcpus boot
parameter, which apparently isn't working. After setting this boot
parameter, I also tried to set the number of vcpus of my Control Domains
with xapi:

xe vm-param-set VCPUs-at-startup=4 uuid=<ControlDomainUUID>
xe vm-param-set VCPUs-max=4 uuid=<ControlDomainUUID>

None of them worked. My domain0 is still seeing only one vcpu. The strange
thing is that XenSource's dom0_mem boot parameter did work as expected, but
domain0_max_vcpus didn't.

Does someone know if XCP/XenServer is somewhere locking the number of
Domain0 vCPUs to only one? Should I try something else?

My main issue is that I have a (very) large number of Networks and VLANs
active inside my XCP pools. And because of that, the xapi process in all
hosts (control domains) constantly hits 100% of cpu usage and all XCP
operations are very slow. Pools may take something close to 3 hours just to
boot, because XCP hosts recreate and synchronize all networks and vlans
right after boot.

Setting the cpu priority of my control domains to higher values already
helped, but I still have many unused cores in my physical machines. Being
able to use them in my busy Domain0s would be very good.

Cheers,

-- Fabio Kung
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