[Bug 703811] [NEW] kvm guest's cpu usage with virtio storage driver goes up to 100% because of flush process

Roman R 703811 at bugs.launchpad.net
Mon Jan 17 07:08:12 UTC 2011


Public bug reported:

Hello,

Problem:
KVM guest's CPU usage goest upto 100% and more (if multi-proc or multi-cores) and makes guest running slowly for period of time when the flush process is running on a virtio storage drive.

How to get this problem:
just start the guest with virtio storage driver and make the guest do some storage related work (ie apt-get install mc) and watch top. after 2-3 sec the cpu usage will go to 100% and guest will run slowly (so slow, that even munin processes cant do their work in 5 minutes and create an e-mail report, that there are  various .lock files present)

host:
ubuntu 10.04.1 LTS
2.6.32-27-server x86_64
2x Intel(R) Xeon(R) CPU E5620 (total of 16 cpus for os)
12GB RAM
2x software raids:
160GB and 2TB
the 160GB one is for system and 2TB one is for kvm images

guest:
Ubuntu 10.04.1 LTS
Disk: virtio
network: virtio


PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND

 869 root      20   0     0    0    0 S   117  0.0   0:17.80 flush-252:0
252 is the vda disk:
monitor at monitor:~$ ls -l /dev/vda
brw-rw---- 1 root disk 252, 0 2011-01-13 16:44 /dev/vda

** Affects: kvm (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/703811

Title:
  kvm guest's cpu usage with virtio storage driver goes up to 100%
  because of flush process



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