RE: [Xen-users] Question about Credit Scheduler!

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

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Rodrigo Lord
> Sent: 29 May 2007 20:41
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-users] Question about Credit Scheduler!
> 
> Hi!
> I'm making some tests in the Xen 3.0.4!
> 
> I would like to know 2 things, for example:
> 
> I have 4 VM's, each VM has 10% of cap (total = 40%)! 
> What it happens with the remaining portion of CPU(60%) ? Has 
> Dom0 a profit? 

If all guests have reached their quota and there's nothing for Dom0 to
then there's nothing but "idle-domain" to run. 

So, the remaining 60% will go to Dom0 (unless Dom0 is also capped, in
which case no domain is "allowed to run"). Note that capping Dom0 may
cause problems, because if Dom0 isn't allowed to run on behalf of a
guest-domain, then the guest-domain requesting Dom0 interaction will
also be blocked until Dom0 can finish the request - so although it is
POSSIBLE to cap Dom0, I wouldn't recommend doing so. 


I guess the word "profit" here is a mistranslation, because there's no
"profit". You may call it a "gain", which is a similar word to profit.
[I'm just trying to clarify if I've missed something in the question,
not complaining about your language skills - mine are much worse in
languages other than English and Swedish]. 

> 
> In another case:
> If I had 4 VM's, each VM has 30% of cap (total = 120%) (Can I 
> do this?)
> What it happens with the excess (20%) ?

Yes, you can do this. Note that the cap is a MAXIMUM TO NOT BE EXCEEDED,
not a minimum, and if any of the domains end up idle for any period of
time, the others will "benefit" from this. If all four domains are
actively using the CPU, then they will all average 25% over a long
time-frame. For a short timeframe, they may vary up and down, up to 30%
as your limit is set (short = tens/hundreds of milliseconds, long = a
few seconds or more). 

It is of course MEANINGLESS to have a total cap of more than 100% if the
guests are permanently using 100% of their allocated CPU-time. It is
meaningfull if you have some guests that are potentially using 100% CPU
time, but you want to make sure that other guests also get a share to
run on the CPU.

Of course, Dom0 will also need to run, so there will not be 100% for the
guests to use on their own, if they are sharing CPU(s) with Dom0. 

--
Mats
> 
> Thanks!
> 
> 



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