libvirt users - Nov 2015 - Re: How to disable kvm_steal_time feature

2015-11-27 16:57 GMT+03:00 Martin Kletzander
<mkletzan@redhat.com>:
> I don't think we report that in domain stats, but top/virt-top could
> help with that.

Ok libvirt can't get this value, but does it possible if i know cpu
stats of domain and host info (i don't know which =)) determine for
specific domain does it possible have steal time or not?

-- 
Vasiliy Tolstov,
e-mail: v.tolstov@selfip.ru

On Fri, Nov 27, 2015 at 05:47:16PM +0300, Vasiliy Tolstov
wrote:
>2015-11-27 16:57 GMT+03:00 Martin Kletzander <mkletzan@redhat.com>:
>> I don't think we report that in domain stats, but top/virt-top
could
>> help with that.
>
>
>Ok libvirt can't get this value, but does it possible if i know cpu
>stats of domain and host info (i don't know which =)) determine for
>specific domain does it possible have steal time or not?
>
I'm not quite sure I fully understand, but if I get that correctly,
you want to know the steal time for a particular domain, right?  To be
honest I'm not sure whether kernel supports steal time reporting
per-process.  I tried searching proc(5) man page, but haven't come to
any satisfiable conclusion.  Maybe someone else has an idea.

Martin

>>
 >> I've read, that disabling 'kvm_steal_time' feature should
workarund
 >> this bug, but i can't find a way to disable it in libvirt's
domain
xmlfile.
 >
 >There is no support for that in libvirt.  Either we must addit ad a
 >feature (patches welcome), but if that's there just for a workaround,
 >I would suggest chasing the original bug.
 >
 >If you just want to check that the workaround works, you could check
 >how the '-cpu ' parameter looks like when the domain is running and
 >then use the unsupported way of adding parameters to the qemu
 >commandline to specify the -cpu parameter again (qemu should use the
 >last one, so it should work), something like this:
 >
 ><domain type='kvm' 
xmlns:qemu='http://libvirt.org/schemas/domain>/qemu/1.0'>
 >...
 > <qemu:commandline>
 >   <qemu:arg value='-cpu'/>
 >   <qemu:arg value='${CPU_SPEC},-kvm_steal_time'/>
 > </qemu:commandline>
 ></domain>
 >
 >where ${CPU_SPEC} is the next parameter after the '-cpu' one from
the
 >command line, so for qemu command line similar to this:
 >
 > qemu-kvm ... -cpu Nehalem,+feat,something ...
 >
 >the line in XML would be:
 >
 > <qemu:arg value='Nehalem,+feat,something,-kvm_steal_time'/>
 >

Thank You Martin, that helped.

Just for information, commit for this bug in kernel:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=7cae2bedcbd4680b155999655e49c27b9cf020fa

Best regards
Piotr Rybicki