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

[Joseph Glanville <joseph.glanville@xxxxxxxxxxxxxx>]

On 3 April 2012 06:03, Mario <mario@xxxxxxxxxxxxxx> wrote:
> On 04/02/2012 09:55 PM, Joseph Glanville wrote:
>>
>> 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.
>>
>
> So what exactly do I do with linux guests that I don't have kernel sources
> for? :-)

Guests older than 2.6.32 could be a problem.
Everything else should be fine.
Anything earlier than 2.6.32 you probably want to run in pure PV mode.

>
>
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Joseph.

-- 
Founder | Director | VP Research
Orion Virtualisation Solutions | www.orionvm.com.au | Phone: 1300 56
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