Re: [Xen-users] XEN hardware compatibility list

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> Having some understanding of the inner workings of the CPU's Speed/Power
> handling, I can see how it would be necessary for the Xen portion to be the
> manager of frequency switching, as Dom0 or DomU doesn't know what's going
> on in any of the other domains per se. I guess it would technically be
> possible to have a monitor process in Dom0 that manages the speed of the
> CPU, but it's probably better to do this in Xen itself.

Yup.  Another thing to consider might be providing Xen interfaces for 
collecting stats and setting the CPU scaling, then allow a userspace daemon 
(e.g. something like cpufreqd) to deal with policy.

It's a bit laptop-centric at the moment but I guess this'll be necessary for 
servers, as their chips also get frequency scaling (I think there are at 
least some Intel chips that do this now).  Of course, if you're running Xen 
you should be getting high server utilisation... ;-)

> However, I don't see the laptop market being a BIG portion of the Xen
> installations, so I'm somewhat dubious as to how much interest there would
> be in this [Yes, I'd love to see it done, but I'm also realistic in the
> expectation of this happening].

*sigh* maybe one day...

> As to hyperthreading or not, I would expect it to be very dependant on the
> behaviour of the application, just as when you're not running Xen. Xen will
> use the two HT "processors" to run on if it's enabled. Whether this gives
> you more, less or the same computing power as one processor depends on what
> your system is doing [You can probably find a benchmark for each of those
> three options, if you look around a bit]. Cache-hit rate, cache-collisions,
> memory bandwidth and many other things will affect the performance in HT
> (as well as in any other processor performance scenario, of course). [By
> the way, it's entirely possible to make a "proper" dual processor system
> run crap too, if you make sure that cache-lines are interchanged due to
> cache-collisions, for instance].

+1, agreed.  The answer with HT is always very much "It depends".  The 
exception is that it's generally a good thing to run dom0 concurrently, in a 
separate thread from the domUs.  This improves IO performance, particular on 
UP systems (not too sure how it fits in the Xen performance picture on SMP 
systems).

Cheers,
Mark

> --
> Mats
>
>
>   _____
>
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of koxman Sent: 27
> July 2005 07:05
> To: Xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-users] XEN hardware compatibility list
>
>
> Hello
>
> I tried both XEN 2.0.6 and 3.0 on my ASUS M6800NE notebook.
>
> 2.0.6 - overheating  and hang  when  start to use  more  CPU (ACPI is not
> present in this version) 3.0    -  runing fine but generaly but integrated
> Broadcom gigabit network card is not working
>
> With both versions is not posible to use cpufreq/speefreq like utilities
> for CPU throtling.
>
>
> Based on my explorations - please can you write down your hw related xen
> experiences?
>
> I am planing to build server for servis DomUÂs - do you have any
> recommendations?
>
> I am looking for something like:
>
> 2xOpteron
> 4GB RAM
> AMD or nForce4 Pro chipset
> RAID 1 from SATA disks
>
> Anybody has some experience with Xen stable on nForce chipset - both
> desktop and server version?
>
> Does it worth to use Hyperthreading on Intel when running Xen?
>
>
> Thanks
>
> koxman

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