Re: [Xen-users] Very bad network performance between domU and dom0

[Klaus Schmidinger <Klaus.Schmidinger@xxxxxxxxxx>]

Petersson, Mats wrote:
>  
> 
>> -----Original Message-----
>> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
>> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
>> Klaus Schmidinger
>> Sent: 25 January 2007 14:45
>> To: xen-users@xxxxxxxxxxxxxxxxxxx
>> Subject: Re: [Xen-users] Very bad network performance between 
>> domU and dom0
>>
>> Petersson, Mats wrote:
>>>  
>>>
>>>> -----Original Message-----
>>>> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
>>>> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
>>>> Klaus Schmidinger
>>>> Sent: 25 January 2007 13:19
>>>> To: xen-users@xxxxxxxxxxxxxxxxxxx
>>>> Subject: [Xen-users] Very bad network performance between 
>>>> domU and dom0
>>>>
>>>> I have a PC with an Intel Core 2 Duo E6600 2,40GHz F1066 CPU
>>>> that runs openSUSE 10.2. The VT feature in the BIOS is enabled.
>>>> The XEN version is 3.0.3_11774.
>>>>
>>>> uname -a:
>>>> Linux tiger 2.6.18.2-34-xen #1 SMP Mon Nov 27 11:46:27 UTC 
>>>> 2006 x86_64 x86_64 x86_64 GNU/Linux
>>>>
>>>> I have two virtual mahines, one running SUSE 8.2, the other 
>>>> Windows XP.
>>>> The Linux machine mounts the /home directory from an 
>> external server
>>>> via NFS, and the Windows machine does the same via Samba. In 
>>>> both cases
>>>> access to the files on the external server is very slow.
>>>>
>>>> My measurements showed that the data transfer rate between the
>>>> external server and my PC that runs the dom0 is about 90MB/s over
>>>> a gigabit ethernet connection, which is perfectly ok.
>>>>
>>>> The same measurements between the dom0 and the Linux domU 
>> machine show
>>>> dom0 -> domU   27.7 MB/s
>>>> domU -> dom0    7.9 MB/s
>>> I take it this is a HVM domain and not a para-virtual kernel?
>> Yes - otherwise I believe wouldn't be able to run Windows XP 
>> as a guest.
> 
> Yes, but you were also talking of Linux guests, which CAN be either - so
> I just wanted to make sure that we're talking about the same thing. 

Ah, I see.

>>>> which is very bad considering that this is all within the same
>>>> hardware and nothing has to go over any external network 
>> connection.
>>>> ifconfig doesn't report any network errors on any of the 
>> interfaces.
>>>> I searched the archive of this ML and came across several threads
>>>> with similar problems, but couldn't find any real solution.
>>>>
>>>> This is a real showstopper for me, because if I can't have good
>>>> access to the NFS/Samba mounted home directory, there's no point in
>>>> using virtual machines at all. So any hints that could help to
>>>> improve this are greatly appreciated.
>>> How have you configured your DomU/Dom0 cpu partitioning? Having one
>> I didn't do anything special about this, so it should be at the
>> default settings.
> 
> Which means "everything on all CPU's". 
>>> dedicated CPU running Dom0 and another running DomU will 
>> help a little
>>> bit because the context switching between the two is a 
>> little bit better
>>> - how much better is a question for debate. 
>>>
>>> Bear in mind tho', that the main culprit here is the fact 
>> that you're
>>> using a emulated network card. It's unlikely that you'll 
>> ever get HIGH
>>> performance with this, because it's just too software 
>> intensive (several
>>> thousand cycles for each intercept by Xen of any operation 
>> that goes to
>>> the hardware). 
>>>
>>> The best solution is to use the para-virtual drivers - 
>> these should (in
>>> theory at least) give you about the same performance as the 
>> para-virtual
>>> kernel does on Xen, because it's using the same method. 
>>>
>>> For linux-2.6, those are available in <xen source
>>> directory>/unmodified_drivers. The README file in that 
>> directoy tells
>>> you how to build these drivers. It's easiest if you do this ON the
>>> target-system. 
>>>
>>> There are drivers for Windows as well, but those are not 
>> available in
>>> source-form, but I believe XenExpress contains drivers for 
>> Windows if
>>> you want to get those. 
>> I just took a look at the XenEnterprise-3.1.0-install.iso and there
>> is a xenserver-client.exe and a xe.exe. I would like to just replace
>> the network driver as necessary, without having to fully install the
>> whole xen thing on my virtual Windows XP machine. Can you give me any
>> hints on how to do this?
> 
> I don't know how you actually install it, but in effect, you'd be
> installing a driver inside your Windows in one way or another. I don't
> think XenServer-client.exe is the right file, but I don't KNOW what the
> file is, so I'm just guessing here - I haven't actually ever used PV
> drivers on any of my virtual machines. 

So are you using PV or HVM on your machines?
Don't you have any problems with slow data transfer between domU and dom0?

Klaus

> --
> Mats
>> Klaus
>>
>>> Mats
>>>> Klaus

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