RE: [Xen-devel] Xen not very green?

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Tom Horsley
> Sent: 30 October 2006 14:35
> To: xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-devel] Xen not very green?
> 
> I was planning on diving into Xen with the release of Fedora
> core 6 and the improved Xen support it has, but one thing
> surprised me: My dual core amd64 system runs more than
> five degrees hotter when idle than the non-Xen kernel
> runs on the same box.

Is your non-Xen kernel running power-management (cpufreq and friends)?
It is possible to do that on Xen also, but it's not compiled in as
standard, and I don't remember if the patch for it is applied to Xen or
you have to get the patch from somewhere... [Although if you run more
than Dom0 on the system, severeal potential problems crop up, the most
immediate one is that Dom0's CPU usages becomes the deciding factor for
the entire system, and the DomU's cpu speed will not be updated by the
changes in the Dom0!]

Of course, there are some other factors that may also affect the power
consumption of the processor: 
1. There is more code to run in Xen - even in "idle". 
2. All of the interrupt handling, task switching, page-table management
and such is more complex with Xen than with the stock linux kernel - all
of which affects even the system when idle, since even an idle system
will do some sorts of "housekeeping behind the scenes" that you don't
necessarily see in the overall performance of the system, but does
happen still. 

This is of course just theories, I haven't actually studied the exact
behaviour of the CPU in the two cases... 

--
Mats
> 
> Is this normal?
> 
> Is the hypervisor missing interfaces to let dom0
> do the energy-star magic for it?
> 
> Is anyone even worried about this?
> 
> Or is it all just a bug with Fedora's kernel?
> 
> Just curious at this point, but it does seem like
> it might be an important issue.
> 
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