[Xen-devel] Re: A credit scheduler issue

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

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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