[Libguestfs] virt-v2v slow when running inside the VM
Sureshkumar Kaliannan
skaliann at gmail.com
Sat Apr 13 00:47:55 UTC 2019
I eliminated software-bridge( using iperf3 bandwidth/latency on the host
and guest was almost the same) and
disk write(using qemu-img convert src dest file both on the host and
guestvm was comprable) being the issue.
Next I profiled both sshd and qemu-img during the conversion phase using
bpftools (profile and tcptop) and this is what i see.
Time (min)
File Size
(KB)
sshd RX
(KB)
tcptop
qemu-img RX
(KB)
tcptop
profile (flamegraph)
0 - 5
5478400
5612971
5601536
qemu-img-0-5.svg
5 - 10
8365440 (+2887040)
5669043
5656517
qemu-img-5-10.svg
10 - 15
8423296 (+57856)
5722376
5708926
qemu-img-10-15.svg
15 - 20
9472128(+1048832)
5708230
5693710
qemu-img-15-20.svg
20 - 25
9540992(+68864)
5723629
5712002
qemu-img-20-25.svg
25 - 30
9617024(+76032)
5721568
5708794
qemu-img-25-30.svg
30 - 35
11263040(+10646016)
5689537
5678589
qemu-img-30-35.svg
35 – 40
11263040(+0)
5722598
5709954
qemu-img-35-40.svg
40 - 45
13252160(+1989120)
5693774
5682506
qemu-img-40-45.svg
45 - 50
15272576(+12020416)
5698998
5686398
qemu-img-45-50.svg
50 - 55
15272704(128)
985500
983322
qemu-img-50-55.svg
Bulk of the write to the "-sda" file completed within 15-20 mins although
sshd/qemu-img receives constant stream of data from the nbd-server
I'm not sure if this is because of "sparseness" (Not sure if the
sparsifying is handled on the nbd-server side or on the receiving side)
The flamegraph also show not much of disk write happening after 20 mins.
(mostly poll and recv_msg)
I am yet todo a similar experiment when running on the "host" to actually
compare the behavior.
Does this provide any clues?
thanks
Suresh
On Wed, Apr 10, 2019 at 10:30 AM Richard W.M. Jones <rjones at redhat.com>
wrote:
> On Wed, Apr 10, 2019 at 10:15:43AM -0700, Sureshkumar Kaliannan wrote:
> > thanks Richard,
> >
> > The experiment was indeed done with nested VM enabled. I am not sure
> about
> > the internals, but i thought once overlay is setup the 2 main processes
> are
> > sshd and qemu-img convert (reading data from sshd and doing the
> conversion)
>
> Yes this should be true. I wouldn't expect copying to be slower.
>
> So initial guess probably wrong. I wonder if there are some extra
> steps such as a slow software bridge or openvswitch on the host?
>
> > I don't see any of the qemu process running.
>
> As per http://libguestfs.org/virt-p2v.1.html#how-virt-p2v-works you
> should see qemu-nbd running on the physical server, and qemu-img
> running on the conversion server during the copying phase.
>
> > Initial overlay setup was pretty quick and rest of the time was spent in
> > qemu-img convert operation
>
> Indeed qemu should exit before copying starts.
>
> Rich.
>
> --
> Richard Jones, Virtualization Group, Red Hat
> http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
> virt-df lists disk usage of guests without needing to install any
> software inside the virtual machine. Supports Linux and Windows.
> http://people.redhat.com/~rjones/virt-df/
>
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