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[Qemu-devel] [Bug 524447] Re: virsh save is very slow

From: dum8d0g
Subject: [Qemu-devel] [Bug 524447] Re: virsh save is very slow
Date: Thu, 24 Mar 2011 12:38:52 -0000

Using ubuntu natty narwhal installed today (2011-03-24) I tried to do a
snapshot with the help of libvirt. Here are the results using natty
version of qemu-kvm and libvirt and using presented slowdown packages.

address@hidden:~# time virsh snapshot-create 1
Domain snapshot 1300968929 created

real    4m39.594s
user    0m0.000s
sys     0m0.020s
address@hidden:~# cd /storage/slowsave/
address@hidden:/storage/slowsave# dpkg -l | grep -E 'libvirt|qemu'              
ii  libvirt-bin                     0.8.8-1ubuntu5                           
the programs for the libvirt library
ii  libvirt0                        0.8.8-1ubuntu5                           
library for interfacing with different virtualization systems
ii  qemu-common                     0.14.0+noroms-0ubuntu3                   
qemu common functionality (bios, documentation, etc)
ii  qemu-kvm                        0.14.0+noroms-0ubuntu3                   
Full virtualization on i386 and amd64 hardware
address@hidden:/storage/slowsave# dpkg -r qemu-common qemu-kvm                  
address@hidden:/storage/slowsave# dpkg -i 
address@hidden:/storage/slowsave# pkill kvm; sleep 5; service libvirt-bin 
address@hidden:/storage/slowsave# time virsh snapshot-create 1
Domain snapshot 1300969754 created

real    2m22.055s
user    0m0.000s
sys     0m0.010s
address@hidden:/storage/slowsave# qemu-img snapshot -l /storage/debian.qcow2 | 
tail -n 1
8         1300969754              57M 2011-03-24 08:29:14   00:03:37.652
address@hidden:/storage/slowsave# virsh console 1
Connected to domain vm
Escape character is ^]

Debian GNU/Linux 5.0 debian ttyS0

debian login: root
Last login: Thu Mar 24 08:15:18 EDT 2011 on ttyS0
Linux debian 2.6.26-2-amd64 #1 SMP Thu Sep 16 15:56:38 UTC 2010 x86_64

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
debian:~# free -m
             total       used       free     shared    buffers     cached
Mem:           561         39        521          0          4         16
-/+ buffers/cache:         19        542
Swap:          478          0        478
address@hidden:/storage/slowsave# dd if=/dev/urandom of=/storage/emptyfile 
bs=1M count=40
40+0 records in
40+0 records out
41943040 bytes (42 MB) copied, 5.4184 s, 7.7 MB/s

I am not sure if my measurements are relevant to anything in here, but I hope 

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  virsh save is very slow

Status in libvirt virtualization API:
Status in QEMU:
  Fix Released
Status in “libvirt” package in Ubuntu:
Status in “qemu-kvm” package in Ubuntu:
  Fix Released
Status in “libvirt” source package in Lucid:
Status in “qemu-kvm” source package in Lucid:
  In Progress
Status in “libvirt” source package in Maverick:
Status in “qemu-kvm” source package in Maverick:
  In Progress

Bug description:
  SRU Justification:
  1. impact: 'qemu save' is slow
  2. how addressed: a patch upstream fixes the case when a file does not 
announce when it is ready.
  3. patch: see the patch in linked bzr trees
  4. TEST CASE: see comment #4 for a specific recipe
  5. regression potential:  this patch only touches the vm save path.

  As reported here: http://www.redhat.com/archives/libvir-

  "virsh save" is very slow - it writes the image at around 1MB/sec on
  my test system.

  (I think I saw a bug report for this issue on Fedora's bugzilla, but I
  can't find it now...)

  Confirmed under Karmic.

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