[fedora-virt] virtio cache mode and windows XP bluescreens

[Dor Laor]

On 11/13/2011 12:29 AM, Tom Horsley wrote:
> I saw a thread a month or so ago on disk performance, and
> just for grins, I thought I'd try different disk cache settings
> for my Windows XP virtual machine that has a qcow2 image
> file (I know qcow2 is never going to be really fast, but I
> thought I'd see if I could get any improvement at all).
>
> Every cache mode I tried (changing them in the advanced
> options of the hardware viewer screen in virt-manager) resulted
> in the XP machine getting into a bluescreen loop when I booted
> it.
>
> Finally set it back to "default" and the XP machine stopped
> getting bluescreens.
>
> Are other cache modes supposed to work OK? Should I
> report a bug on some component? Should I try and capture
> the bluescreen content? (It flickers in and out really fast).
>
> The main reason I was trying this is because it sure seems
> like the qcow2 image gets slower and slower every time I
> upgrade fedora and get new and improved qemu and libvirt
> code. I don't have solid benchmarks, but it sure feels
> slower. Has optimization of cases that are supposed to be fast
> slowed down qcow2 somehow?
>
> I'm currently trying to build an updated base image by
> doing the trick of writing a giant file of zeros to fill
> up the disk so I can then convert the mostly zero image to
> a new qcow2 file, and the rate it is going makes it seem like
> it may well be tomorrow before it finishes writing the
> 10 GB or so of zeros it needs to finish filling up the
> disk image.
>
> None of my CPUs are showing over 1% utilization and gkrellm
> is showing only 2.0M disk write rate, so it sure seems like
> all the components involved are spending more time just
> waiting than anything else.

We need more details - guest/host versions, whether you use virtio or 
ide, in case of virtio, what's the win pv version, etc.

cache=off and cache=writeothrough are safe and pretty much bugfree so I 
doubt the root cause is there. In addition, latest qcow2 code should 
perform relatively good, so please provide more details

> _______________________________________________
> virt mailing list
> virt at lists.fedoraproject.org
> https://admin.fedoraproject.org/mailman/listinfo/virt