Re: [Xen-users] a question with gplpv

[Lu Fengqi <curiouslfq@xxxxxxxxx>]

I change another host(xen master) for test, the backend indeeds become blkback.

However in the xen 4.1.2, `xm create` will return this error message:

xm create win_pvhvm.cfg
Using config file "./win_pvhvm.cfg".
Error: Cannot configure device for unknown backend backendtype=phy

`xl create` seems ok, but the backend is still qdisk.

I must use `losetup` attach this file to a loop device, and use disk=[ 'phy:/dev/loop0,hda,w', ]

Thank you.

2016年9月7日星期三，Juergen Gross <jgross@xxxxxxxx> 写道：

On 07/09/16 10:03, Lu Fengqi wrote:
> Excuse me, I modify the config and create the guest, but the
> xenstore-ls command's output show me that the guest use the qdisk as
> the backend.
> The guest os was installed in hvm mode. And, I install gplpv driver
> for it and change  "disk = [ 'file:/home/xen/win.img,hda,w' ]" to
> "disk = [ 'file:/home/xen/win.img,hda,w,backendtype=phy' ]".

Hmm, strange. Just tested it on my machine, works without problem:

# xenstore-ls /local/domain/4/vbd
 vbd = ""
  768 = ""
   backend = "/local/domain/0/backend/vbd/4/768"
...

with:

disk=[ 'file:/home/vm/images/tw,hda,w,backendtype=phy', ]

for the disk definition.

Could it be your dom0 kernel doesn't have xen_blkback or it isn't
loaded? You can check via:

lsmod | grep xen_blkback

In case it doesn't show up try

modprobe xen_blkback

and then check for it again via lsmod.

> Do you have any idea about this? Moreover, can you tell me which
> backendtype can provide the best io performance? Thanks anyway.

I'm not sure about the numbers. I'd expect the kernel based backend
(phy) to be faster than qdisk, but this is just a gut feeling which
isn't based on any measurement.


Juergen

--

-------------------------------------------------------------

Thanks,

Lu

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