Re: [Qemu-discuss] [kubevirt-dev] Re: Converting qcow2 image on the fly to raw format

[Nir Soffer]

On Thu, Jul 19, 2018 at 10:24 PM Richard W.M. Jones <address@hidden>
wrote:

> On Thu, Jul 19, 2018 at 09:50:00PM +0300, Nir Soffer wrote:
> > On Mon, Jul 16, 2018 at 11:56 AM Daniel P. Berrangé <address@hidden
> >
> > wrote:
> > ...
> >
> > > Recommendation is to run 'qemu-img info' to extract the metadata and
> sanity
> > > check results eg no backing file list, not unreasonable size, etc. When
> > > running 'qemu-img info' apply process limits of 30 secs CPU time, and
> 1 GB
> > > address space.
> > >
> >
> > Can you explain the values of cpu seconds and addres space?
> >
> > Also, I tried to use prlimit --rss=N, and the value seems to be ignored.
> Is
> > this
> > a bug in prlimit?
>
> This is the code in OpenStack:
>
>
> https://github.com/openstack/nova/blob/50f40854b04351fb622fd8b68b374a8fe8ca2070/nova/virt/images.py#L74
>
>
> https://github.com/openstack/oslo.concurrency/blob/a9d728b71e47540fd248a6bc2d301fdfa9a988ce/oslo_concurrency/processutils.py#L194
> (see prlimit)
>

Thanks for the links.

The 30 seconds cpu_time time limit confuses me; it was added in:
https://github.com/openstack/nova/commit/011ae614d5c5fb35b2e9c22a9c4c99158f6aee20

The patch references this bug:
https://bugs.launchpad.net/nova/+bug/1705340

The bug show that qemu-img info took more then 8 seconds real time:

/usr/lib/python2.7/site-packages/oslo_concurrency/processutils.py:355
2017-07-19 19:47:42.849 7 DEBUG oslo_concurrency.processutils
[req-7ed3314d-1c11-4dd8-b612-f8d9c022417f
ff236d57a57dd42cb5811c998e30fca1a76233873b9f08330f725fb639c8b025
9776d48734a24c23a4aef51cb78cc269 - - -] CMD "/usr/bin/python2 -m
oslo_concurrency.prlimit --as=1073741824 --cpu=16 -- env LC_ALL=C
LANG=C qemu-img info
/var/lib/nova/instances/_base/41ebff725eab55d368f97bc79ddeea47df894145.part"
returned: 0 in 8.639s execute

How the size of the snapshot can slow down reading the qcow2 header?
Is this relevant for qemu-img-rhev 2.10?

Nir