Lars Kellogg-Stedman
2016-Mar-04 16:14 UTC
[libvirt-users] Why are virsh vol-upload/vol-download so slow?
I was interested in using 'virsh vol-upload' and 'virsh
vol-download',
rather than mucking about directly with the filesystem. But while
simply copying the image is relatively quick:
# ls -l /var/lib/libvirt/images/centos-7-cloud.qcow2
-rw-r--r--. 1 qemu qemu 1004994560 Apr 15 2015 centos-7-cloud.qcow2
# time cp /var/lib/libvirt/images/centos-7-cloud.qcow2 /tmp/myimage.qcow2
real 0m10.829s
user 0m0.024s
sys 0m1.668s
Trying to do the same thing with `virsh vol-download` is glacial:
# time virsh vol-download --pool default centos-7-cloud.qcow2
/tmp/myimage.qcow2
I killed it after 10 minutes:
real 10m20.775s
user 10m19.451s
sys 0m1.887s
After which is was about halfway through:
# ls -l /tmp/myimage.qcow2
-rw-r--r--. 1 root root 564920248 Mar 4 11:11 /tmp/myimage.qcow2
What is up with that?
--
Lars Kellogg-Stedman <lars@redhat.com> | larsks @
{freenode,twitter,github}
Cloud Engineering / OpenStack | http://blog.oddbit.com/
Daniel P. Berrange
2016-Mar-04 16:57 UTC
Re: [libvirt-users] Why are virsh vol-upload/vol-download so slow?
On Fri, Mar 04, 2016 at 11:14:44AM -0500, Lars Kellogg-Stedman wrote:> I was interested in using 'virsh vol-upload' and 'virsh vol-download', > rather than mucking about directly with the filesystem. But while > simply copying the image is relatively quick: > > # ls -l /var/lib/libvirt/images/centos-7-cloud.qcow2 > -rw-r--r--. 1 qemu qemu 1004994560 Apr 15 2015 centos-7-cloud.qcow2 > # time cp /var/lib/libvirt/images/centos-7-cloud.qcow2 /tmp/myimage.qcow2 > real 0m10.829s > user 0m0.024s > sys 0m1.668s > > Trying to do the same thing with `virsh vol-download` is glacial: > > # time virsh vol-download --pool default centos-7-cloud.qcow2 /tmp/myimage.qcow2 > > I killed it after 10 minutes: > > real 10m20.775s > user 10m19.451s > sys 0m1.887s > > After which is was about halfway through: > > # ls -l /tmp/myimage.qcow2 > -rw-r--r--. 1 root root 564920248 Mar 4 11:11 /tmp/myimage.qcow2 > > What is up with that?What version of libvirt ? We had an unfortunate implementation mistake which caused us to waste tonnes of time in memmove(). versions since 1.2.19 have a fix that addresses it commit d9c9e138f22c48626f719f880920e04c639e0177 Author: Ossi Herrala <oherrala@gmail.com> Date: Mon Jul 20 12:44:32 2015 +0000 rpc: Fix slow volume download (virsh vol-download) Use I/O vector (iovec) instead of one huge memory buffer as suggested in https://bugzilla.redhat.com/show_bug.cgi?id=1026137#c7. This avoids doing memmove() to big buffers and performance doesn't degrade if source (virNetClientStreamQueuePacket()) is faster than sink (virNetClientStreamRecvPacket()). Resolves: http://bugzilla.redhat.com/1026137 Signed-off-by: Martin Kletzander <mkletzan@redhat.com> Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|
Lars Kellogg-Stedman
2016-Mar-04 17:09 UTC
Re: [libvirt-users] Why are virsh vol-upload/vol-download so slow?
On Fri, Mar 04, 2016 at 04:57:30PM +0000, Daniel P. Berrange wrote:> What version of libvirt ? We had an unfortunate implementation mistake > which caused us to waste tonnes of time in memmove(). versions since > 1.2.19 have a fix that addresses itAh, this is on F23, which has: libvirt-1.2.18.2-2.fc23.x86_64 There's nothing more recent right now in either updates or updates-testing (and I was hoping to target (RHEL/CentOS)7, which have libvirt-1.2.17-13.el7_2.2.x86_64). Thanks, -- Lars Kellogg-Stedman <lars@redhat.com> | larsks @ {freenode,twitter,github} Cloud Engineering / OpenStack | http://blog.oddbit.com/