libvirt users - May 2019 - Re: Running all my virtual machines with a low priority

> You would have to set the priority of all vCPUs in each guest, as well
> as emulator threads in each guest (the latter needs very new libvirt).
This does not seem a viable option then with Ubuntu 18.04. And changing XML on
all guest VMs is extra work.

Is there no other way? For example, are all such virtual machines not some
daemon or systemd unit or set of units? Would it be feasible to lower the
priority on all of those? Or is that not easy to do either?

Thanks again,
   rdiez

On Wed, May 01, 2019 at 11:58:23AM +0200, R. Diez wrote:
>
>> You would have to set the priority of all vCPUs in each guest, as well
>> as emulator threads in each guest (the latter needs very new libvirt).
>
>This does not seem a viable option then with Ubuntu 18.04. And changing XML
on all guest VMs is extra work.
>
>Is there no other way? For example, are all such virtual machines not some
daemon or systemd unit or set of units? Would it be feasible to lower the
>priority on all of those? Or is that not easy to do either?
>
I'm not sure if we're resetting all the cgroup values, so it should be
possible
by setting this for the machine.slice cgroup (or somewhere around there) which
would make it effective for all the VMs, right?  I have not tested it, though,
sorry.
>Thanks again,
>   rdiez
>
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On Thu, May 02, 2019 at 11:33:06AM +0200, Martin Kletzander
wrote:
> On Wed, May 01, 2019 at 11:58:23AM +0200, R. Diez wrote:
> > 
> > > You would have to set the priority of all vCPUs in each guest, as
well
> > > as emulator threads in each guest (the latter needs very new
libvirt).
> > 
> > This does not seem a viable option then with Ubuntu 18.04. And
changing XML on all guest VMs is extra work.
> > 
> > Is there no other way? For example, are all such virtual machines not
some daemon or systemd unit or set of units? Would it be feasible to lower the
> > priority on all of those? Or is that not easy to do either?
> > 
> 
> I'm not sure if we're resetting all the cgroup values, so it should
be possible
> by setting this for the machine.slice cgroup (or somewhere around there)
which
> would make it effective for all the VMs, right?  I have not tested it,
though,
> sorry.
You could perhaps set  'cpu.shares' cgroup setting on /machine.slice.
This isn't really a nice level in the traditional sense, rather it is
a relative weighting evaluated against other cgroups at the same level.
So if you change it from 1024 to 512, then processes under /machine.slice
will get 1/2 the CPU time vs stuff under /system.slice or /user.slice,
when there is contention for CPU time. 

Regards,
Daniel
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