Re: [Xen-users] HVM on 3.2 kernel hdd speed issue

[Joseph Glanville <joseph.glanville@xxxxxxxxxxxxxx>]

On 3 April 2012 05:48, Mario <mario@xxxxxxxxxxxxxx> wrote:
> On 04/02/2012 09:27 PM, Joseph Glanville wrote:
>>
>> On 3 April 2012 05:17, Mario<mario@xxxxxxxxxxxxxx>  wrote:
>>>
>>> On 04/02/2012 08:45 PM, Joseph Glanville wrote:
>>>>
>>>>
>>>> On 2 April 2012 22:49, Mario<mario@xxxxxxxxxxxxxx>    wrote:
>>>>>
>>>>>
>>>>> On 04/02/2012 01:55 PM, Heiko Wundram wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>> Am 02.04.2012 13:33, schrieb Mario:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On 04/02/2012 12:19 PM, Heiko Wundram wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> Windows, of course, does not natively support PVonHVM in any way
>>>>>>>> (except
>>>>>>>> when using corresponding drivers to enable that), so if you get
>>>>>>>> excessively slower I/O-speeds on "fully" virtualized Linux DomUs
>>>>>>>> than
>>>>>>>> you do on Windows DomUs which _don't_ have the corresponding
>>>>>>>> PV-drivers
>>>>>>>> installed, something else is amiss here; it'd help if you could
>>>>>>>> describe
>>>>>>>> your setup in a little more detail.
>>>>>>>>
>>>>>>>
>>>>>>> Why are we still on PVonHVM subject? I do not want that, I want
>>>>>>> regular HVM to work with linux domU's the same way it works with
>>>>>>> windows domU's. I don't have the luxury to install custom drivers on
>>>>>>> some domU's, so there is no point in trying to force me to use
>>>>>>> PVonHVM
>>>>>>> because i can't.
>>>>>>> So, anyone else please? :-)
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> Read my last paragraph again, please: Linux fully virtualized DomUs
>>>>>> (which use the corresponding NIC and disk emulation as implemented by
>>>>>> qemu) shouldn't perform any different than a Windows DomU,
>>>>>> I/O-performance wise, as both of them use the same infrastructure in
>>>>>> Dom0 to do I/O (qemu process). You're saying that they are different,
>>>>>> I/O-wise, so: please be a little more concrete _what_ the problem is
>>>>>> that you're seeing. We don't have crystal balls handy, sorry.
>>>>>>
>>>>>
>>>>> Its actualy quite simple, here is an example: Windows hvm domU disk io
>>>>> on
>>>>> my
>>>>> test server is ~60MB/s (sequential read or write). Linux HVM guests
>>>>> (using
>>>>> same config file template) on the same server gives ~10MB/s (sequential
>>>>> read
>>>>> or write), i tried pretty much everything, from tuning scheduler to
>>>>> changing
>>>>> kernel. I am not sure what to do with it, other then roll back to
>>>>> kernel
>>>>> 2.6.34 on my dom0.
>>>>
>>>>
>>>>
>>>> Hieko and myself have told you what to do to get decent performance.
>>>> Some examples of fully setup PVonHVM guests are available on my file
>>>> mirror.
>>>> http://mirror.orionvm.com.au
>>>>
>>>> Unless you use the PV drivers there isn't really a whole lot more I
>>>> can do for you.
>>>>
>>>> I can't explain why performance would differ under 2.6.34 vs 3.2.
>>>> This makes no sense as qemu-dm runs in userspace. You would have had to
>>>> make
>>>> some changes to the toolstack for this performance to differ.
>>>>
>>>
>>> Performance difference between dom0 kernels aside, what I don't
>>> understand
>>> is why windows HVM domU works fine, while linux doesn't?
>>> Isn't HVM supposed to work same for every guest, or does linux actualy
>>> have
>>> something against HVM mode? I simply don't get it.
>>
>>
>> It's definitely not an optimized use case however I have never seen as
>> low performance as you are reporting.
>> There are too many reasons to list as to why performance between
>> Windows HVM and Linux HVM would differ.
>>
>> What Linux guests are you attempting to run?
>>
>> Joseph.
>>
>
> Running a slackware guest, tried various kernels, did not make any
> difference. Windows in question is 2008 R2.

Try using a 3.0 guest kernel with XEN_PLATFORM_PCI=y and all of the
Xen device drivers.
This will enable PVHVM and you should be right as rain for performance.

>
>
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