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

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?


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