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[Xen-devel] Re: A credit scheduler issue

On 30 Jun 2006, at 02:13, Kamble, Nitin A wrote:

   While debugging I notice an odd behavior; When running on a 2 CPU system, dom0 gets 2 vcpus by default. And even if there are no other domains running in the system,  the dom0 vcpus are getting migrated to different pcpus in the load balance. I think it is due to the preemption happening in the credit scheduler; and it is not necessary and is actually wasteful to move vcpus when no of vcpus in the system are equal to no of pcpus.     I would like to know your thinking about this behavior. Is it an intended in the design?
I added this small fix to the scheduler to fix this behavior. And with it I see the stability of Xen improved. Win2003 boot was crashing with unhandled MMIO error on xen64 earlier with credit scheduler. I am not seeing that crash with this small fix anymore. It is quiet possible that there are more bugs I need to catch for HVM domains in the credit scheduler. And I would like to know your thoughts for this change.

Although you may have spotted a performance bug that should be looked into (if this migration happens significantly frequently), it *should not* be a correctness bug! I don't think the fixes for the HVM-and-credit-sched bugs lie in the credit scheduler itself. :-)

 -- Keir

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