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[Xen-users] Relation between vcpu and sched-credit -c (caping parameter)

  • To: xen-users@xxxxxxxxxxxxxxxxxxx
  • From: "Jordi Segues" <jordisd.mailing@xxxxxxxxx>
  • Date: Tue, 3 Apr 2007 18:53:49 +0200
  • Delivery-date: Tue, 03 Apr 2007 09:52:50 -0700
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  • List-id: Xen user discussion <xen-users.lists.xensource.com>


I'm playing with xen 3.0, and cpu load balancing between domUs.

So to resume,

- VCPU are used to divide processors in order to allow some domUs to
use a bigger part of the processor than other domUs, or some
processors in parallel.
- xm sched-credit -d domu -w 512 increases the priority of the domu (the weight)
- xm sched-credit -d domu -c 50 (cap) fixes the max processor
percentage a domu can use.

So the cap option is a physical CPU percentage I've seen in the manual.
But I don't understand its relation with VCPUs allocated to the domu
in wich we modify caping.

Is the cap parameter proportional to the VCPUs allocated, or
proportional to the total CPU power? Because if a domu does'nt have
acces to a CPU (in case a VCPU is not pinned to it), why would the
caping parameter be relationed to it?

I don't know if I am clear, please let me know.
Thanks a lot.



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