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

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Very bad network performance between domU and dom0
From: Klaus Schmidinger <Klaus.Schmidinger@xxxxxxxxxx>
Date: Thu, 25 Jan 2007 16:02:26 +0100
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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 #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?


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

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