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Re: [Xen-users] Improve performance of domain U

To: "Steffen Heil" <lists@xxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] Improve performance of domain U
From: "saptarshi naha" <naha80@xxxxxxxxx>
Date: Sun, 3 Sep 2006 18:41:28 +0530
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Thanks a lot Steffen and Fabrice, considering its a weekened.

> 1. I wanted to know if there are any configuration changes I
> can make to improve the performance of domain U?

You will need to expose more of your setup.
LVM devices are typically faster than loopback file devices.
Other things might help as well. Give us more information.

I am doing LVM and then GNBD for domain U's. Is there a better way of
doing to improve performance? I have dell power edges with scsi

> 2. Domain U have no /boot sector in /etc/fstab. It is all a
> single partition in / . I wanted to know if there are any
> shortcoming to just having / partition to performance?

I am also unsure about that point.

I am not SURE  but maybe it is to prevent boot sector from being
corrupted.  But then that has NO connection to performance.

> 3. Also can the domain U be given swap space to improve
> performance? I am guesssing thats the swap is used from
> domain 0 which was added during inital installation.

Yes, just pass another device in and "swapon" it in domU. You should use a
real partition or LVM device for that.
Swap for dom0 is NOT used inside domUs. Every domain has it's own memory and
needs to swap on it's own.
(Yes, in my view this is a shortcoming of Xen, as it can force one domain to
swap out things it need frequently while another domain uses memory for
things it does not really need. However it seems to be the only way to be
fair. Otherwise any domain cound directly affect other domain's

Great reply, thnaks.

I will create the swap using LVM and GNBD and then pass the swap
partition using /dev/sda2 through configuration files. Correct me if
am wrong.

> 4. Is the performance of teh domain U dropped due to internal
> networking through bridging? I wanted to know if anyone knows
> how to fine tune it to improve performance.

I am also unsure here. I don't think the bridge itself adds any noticeable
load (there are performance benchmarks for netfilter with 3.500.000
concurrent connections and 60.000 connects per second.), BUT the indirection
of the virtual network interfaces inside the domUs means that any packet
which is ready to send is only written to a buffer and will only be send,
when the control is given back to dom0, which is the only domain that can
really send...

Not SURE, Can giving the MAC and IP address in the Xen configuration
file make any difference to internal networking performance?

Right now, I have just made the changes in the domain U using
"netconfig" and that sticks onto the domains. Also when I do ifconfig
in domain 0 there is no MAC and no IP for vif0.1 and vif0.2 (which are
my domain U).

So I think it might be usefull to have a own NIC in the domU using pci
passthrough, however that's not possible in my environment (especially with
a lot of domUs), and so I didn't (or couldn't) try...

Coz the thread is going so well I am tempted to ask 1 more question.

Is it possible to do windows installation on Xen with Xeon processors
but without dual core? I search on the intel site and xensource but
there is no mention for JUST xeon processor have intel VT techonology.

If it is not possible, Is there any way of doing windows
virtualization i can try?

Thanks a lot,

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