Xen devel - Jul 2008 - XEN CPU scheduler (was: CPU load balancing)

Hi all.

I would understand some things about credit scheduler of XEN: 
- How is computed the credits? Is it dependent of domain weight?
- How the over priority becomes an under? If a domain uses 100% of CPU because
the others are in ''Idle'', what occurs when the 4 other domains
wake up? Is it possible to affirm (and guarantee) that each of domains (Dom0 + 4
DomU) uses 20% of CPU if their weights are the same?

I tried to find the information in maillists archives and on Internet, but
except some problems during introduction phase of
 scheduler, I did not find responses.

Thank for your answers.

Best regards,

-- 
Andreï V. FOMITCHEV


--- En date de : Jeu 24.7.08, Andreï V. Fomitchev <fomitchev@yahoo.fr> a
écrit :
De: Andreï V. Fomitchev <fomitchev@yahoo.fr>
Objet: Re: [Xen-users] CPU load balancing
À: xen-devel@lists.xensource.com, xen-users@lists.xensource.com
Date: Jeudi 24 Juillet 2008, 11h44

Thank you Gabriel for the document. I found it very interesting and instructive.
Now, I understand that my idea is useless and
 childish.
I want to improve my knowledge of schedulers. I found in Xen Wiki an article
about Credit Scheduler (a priori, it is the default scheduler in XEN now).
I use the backported XEN 3.2 on a Debian Etch. 
Is it possible to test the work-conserving (WC) and non work-conserving (NWC)
modes?
Is it possible to test the other schedulers (BVT and SEDF)?

Best regards,

-- 
Andreï V. FOMITCHEV

--- En date de : Jeu 24.7.08, Gabriel Southern <gsouther@gmu.edu> a
écrit :
De: Gabriel Southern <gsouther@gmu.edu>
Objet: Re: [Xen-users] CPU load balancing
À:
 fomitchev@yahoo.fr
Cc: xen-devel@lists.xensource.com, xen-users@lists.xensource.com
Date: Jeudi 24 Juillet 2008, 0h46

I''m not sure if the idea you are proposing is really useful.  The
credit scheduler will already allocate unused CPU time to other VMs,
if you don''t have a cap configured, it does not necessarily follow
weight percentage allocation exactly.

You might find this research paper helpful:
http://www.cs.ucsd.edu/~dgupta/papers/per07-3sched-xen.pdf

On Wed, Jul 23, 2008 at 5:39 AM, Andreï V. Fomitchev
<fomitchev@yahoo.fr> wrote:
> Hi all.
>
> I continue to study the XEN possibilities and currently I search a
''CPU load
> balancing tool'' which answers the scenario below:
> Configuration: using sched-credit command, the 4 DomU are the same weight
> and each uses only 15% of CPU.
> The balancing tool monitors the DomU CPU loads and if two (or

 more)
> consecutive measures of CPU load equal to 100% of CPU and if the other
> domains are in Idle mode, the tool increases the Domain weight and
allocates
> more of CPU. When the Domain terminated and  "returns" to Idle,
the tool
> returns the Domain configuration in nominal mode.
>
> 1) Because I did not find a response in XEN documentation, my first
> questions are "philosophical":
>  - this kind of tools is it interesting? Can it provide some improvements
of
> performances on-the-fly?
>
> 2) I found some tools which manage the load balancing of entire clusters.
I
> think that it is possible to adapt them or their algorithm to CPU
balancing
> but I think also that I am not the first to meet this issue... Did you
read
> something about a tool which can answer my needs?
>
> Thank you for your answers.
>
> Best

 regards,
>
> --
> Andreï V. FOMITCHEV
>
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