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[Xen-devel] ip stealing, cpu qos, and hyperthreading

To: xen-devel@xxxxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] ip stealing, cpu qos, and hyperthreading
From: Matt Ayres <matta@xxxxxxxxxxxx>
Date: Thu, 11 Nov 2004 17:00:21 -0500
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I've been experimenting with Xen on and off for the past couple months
and it's come a long way and the roadmap looks great. What really made
it a possibility for me was the loopback support for vbd's. I'm getting
pretty far with it, but I have a few questions that hopefully I can get

1) IP Stealing - I want to be able to assign IP's to a domain and for it
to be limited to them only.  I tried setting the anti-spoof option to on
in the xend config file and it seemed to add a rule to the FORWARD table
that matched base on the physdev eth0, but it just blocked any domain
from accessing the network.  I was setting the IP using the "ip" config
parameter in the domains config file.  Is there also a way to assign
multiple IP's, perhaps multiple ip config options or comma deliminted? 
If the anti-spoof isn't what I think is it, would using something like
ebtables be usable to provide what I want to do?  My problem is it looks
like the bridge interface is based on the domain id and domain id's are
still dynamically assigned (poor IMHO).  What is the status on static
domain id's?  It'd be good for many things, another problem is the
telnet console is based off of the domain id... if I handed a Xen server
off to a customer i'd have to basically write an interface that they'd
have to log in to to find out what port they should use since the last
server reboot, it'd be easier to just say "telnet to this host on port
9605 to gain access".

2) CPU QoS - This looks good, even though this is for selling a service
where each customer should receive their guaranteed amount it looks like
the atropos scheduler is broken and it's better to use BVT for now. 
What i'm confused on is how to break down the numbers based on what kind
of priority each domain should get.  ie. If I want the base accounts to
get a priority of 1 out of 4, next 2 out of 4 (total units).  That
doesn't even make complete sense to many of you as i'm really that
confused as to what to set these variables to.  Are there any more
specific documents or example configs for using the CPU schedulers?

3) HyperThreading - Good or bad with Xen?  I'd be using the 2.6 kernel
for domain0 which I believe has full SMT support so I would assume
good.  Also, since each domain is assign 1 CPU this would make the
possibilities out of 4 instead of 2 so i'm not sure if that benefits
over the SMT scheduler or if domains are even threaded so they benefit
from having the extra logical CPU's and it just makes the load un-even
and increases scheduling latency.

4) I/O QoS - This is just round robin for now?  I see it on the
roadmap.  I have already envisioned the scenario with someone purchasing
a server with 64MB physical ram and adding a 512MB swap file inside
their server and just completely thrashing the disks.  Is the current
system good enough to handle this (assuming some good SCSI disks are
being used) ?

Any answers to these questions would be great.  I'm also all geared up
for some discussion/arguing :)

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