[fedora-virt] Disk device performance in F11

Dor Laor dlaor at redhat.com
Tue Jun 30 06:31:01 UTC 2009

On 06/29/2009 08:38 PM, Jerry James wrote:
> I'm having a problem with a virtual machine created on an F-11 host
> that I didn't have with an F-10 host, and I'm wondering if I've
> misconfigured something or missed a trick somewhere.  I'm doing some
> custom Linux kernel work for my employer, and I'm using a small
> collection of virtual machines to test it.  In the short time I've had
> F-11 on my host machine, I've seen that virtual disk performance is
> noticeably worse than it was with F-10.  My virtual machines regularly
> spew soft lockup messages to the system log, always with backtraces
> that show the process is being starved of the disk.  The tests put a
> lot of stress on the disk, because this custom kernel work is going to
> help some overloaded servers deal with the load.
> It's actually working pretty well on the real machines with real
> disks, but with the upgrade to F-11, my test VMs have become almost
> useless for testing further development work.  Before I take the
> drastic step of rolling back to F-10, what factors affect the virtual
> disk performance?
> I created both the F-10 and F-11 machines with virt-manager, if that matters.
> Thanks,

It might be due to different image caching defaults.
Can you grab the current command line of qemu and change -drive 
file=xxxx,..,cache=writeback and retest?

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