libvirt users - Jul 2014 - Re: memoryStats question

At Fri, 04 Jul 2014 16:18:45 +0200,
Ján Tomko wrote:
> 
> [1  <text/plain; ISO-8859-1 (quoted-printable)>]
> On 07/04/2014 03:18 PM, Claudio Bley wrote:
> > At Thu, 03 Jul 2014 17:46:14 +0300,
> > Gleb Voronich wrote:
> >>
> >>
> >>> virDomainMemoryStats() gets those stats, if qemu is new enough
to
> >>> provide them, and if the guest cooperates to provide them.
> >> Well I use the latest QEMU 2.0.0
> >> I have the latest CentOS 6.5 installed on the guest and
unfortunately
> >> I can't get more stats that I have.
> >>
> >>> Which OS are you using in your guests?
> >>>
> >>> Of course, you need to have the virtio balloon driver up and
runnig in
> >>> your guests.
> >> CentOS 6.5 x86_64
> >> It has the balloon driver and it is up and running:
> >>
> >> # modinfo virtio_balloon
> >> filename:
> >>
/lib/modules/2.6.32-431.17.1.el6.x86_64/kernel/drivers/virtio/virtio_balloon.ko
> >> license:        GPL
> >> description:    Virtio balloon driver
> >> srcversion:     BB9F75B2CAF3435CC507998
> >> alias:          virtio:d00000005v*
> >> depends:        virtio,virtio_ring
> >> vermagic:       2.6.32-431.17.1.el6.x86_64 SMP mod_unload
modversions
> > 
> > In this case, it's your guest kernel that's too old to support
these
> > stats.
> > 
> > Apparently, reporting statistics in the balloon driver was introduced
> > in the kernel on 24th Feb 2010 (commit
> > 9564e138b1f6eb137f7149772438d3f3fb3277dd) which clearly predates
> > version 2.6.32 (2nd December 2009).
> 
> Acording to the kernel RPM's changelog, this was backported into
2.6.32-38.el6
> and released in RHEL 6.0 (Nov 2010):
> https://bugzilla.redhat.com/show_bug.cgi?id=601690
In that case, I'd guess that Gleb just forgot to call
virDomainSetMemoryStatsPeriod, perhaps?

Gleb, you didn't mention what language (binding) you're using.

In virsh, use the "--period N" option for the dommemstat command at
least
once in order to enable stats collection.

-- 
Claudio

> In that case, I'd guess that Gleb just forgot to call
> virDomainSetMemoryStatsPeriod, perhaps?
I've just performed the same test with CentOS 7 at the host and CentOS 7 
at the guest.
Everything works.

# virsh dommemstat vm1
actual 1048576
swap_in 0
swap_out 0
major_fault 751
minor_fault 3958627
unused 375900
available 1017988
rss 978248

I don't know the reason it doesn't work with ELRepo 3.10.45 kernel but 
I'd really like to.
According to https://bugzilla.redhat.com/show_bug.cgi?id=601690 
memoryStats should work at host's side starting from 2.6.32-52.el6 so I 
suppose the problem is the guest kernel.

Do you think this could be caused by an old version of virtio_balloon 
driver?

At Tue, 08 Jul 2014 18:21:54 +0300,
Gleb Voronich wrote:
> 
> 
> > In that case, I'd guess that Gleb just forgot to call
> > virDomainSetMemoryStatsPeriod, perhaps?
> I've just performed the same test with CentOS 7 at the host and CentOS
> 7 at the guest.
> Everything works.
> 
> # virsh dommemstat vm1
> actual 1048576
> swap_in 0
> swap_out 0
> major_fault 751
> minor_fault 3958627
> unused 375900
> available 1017988
> rss 978248
> 
> I don't know the reason it doesn't work with ELRepo 3.10.45 kernel
but
> I'd really like to.
> According to https://bugzilla.redhat.com/show_bug.cgi?id=601690
> memoryStats should work at host's side starting from 2.6.32-52.el6 so
> I suppose the problem is the guest kernel.
> 
> Do you think this could be caused by an old version of virtio_balloon
> driver?
Maybe. It's hard to tell without exactly knowing what you did...

Try turning on debugging output for libvirtd in order dig into this.

But, since it works in general, it rules out libvirt to be at fault
here. You may have better luck asking on the qemu-user list.

For me, it works with kernel 2.6.32-431.el6.x86_64 from CentOS 6.5.

-- 
Claudio