Re: [Xen-users] Windows PV drivers destroying performance

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Fri, 2015-07-24 at 22:14 +1000, G Crowe wrote:
> I installed the PV drivers in some windows PVs as I thought it would 
> improve performance, but the systems then became painfully slow to use.
> 
> I ran some tests on hard disc performance on a newly installed Win7 32 
> bit system before and after installing the PV drivers from univention.de 
> (version 0.11.0.373) as the other sites appear to be offline. The host 
> machine is running Fedora 21 with kernel 3.19.3.
> Without the PV drivers (with QEMU hardware) hard disc performance was 
> 4409 I/O per second and 9.03Mbps.
> With the PV drivers installed this dropped to 207 I/O per second and 
> 0.43Mbps.
> 
> Without the PV drivers, the remote desktop screen would refresh almost 
> instantly, but with the PV drivers it could take up to 10 seconds just 
> to refresh the screen.
> 
> I don't understand this, as I though that the sole purpose of the PV 
> drivers was to improve I/O performance,

Your expectation here is correct.

>  yet they have made the system so 
> slow that it is virtually unusable.
> 
> Am I doing something wrong here?

It seems unlikely, I don't think there is much you can have done wrong,
it's supposed to just work ;-) more likely some sort of bad interaction
between some (possibly buggy) component and another.

I don't know much about the Windows PV drivers, so hopefully someone else
can chip in with some tips/knowledge.

Seeing your guest cfg file and any relevant logs from /var/log/xen might
have some sort of clue.

Ian.

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