Re: [PATCH] allow vcpu to move between pcpus (was Re: [Xen-ia64-devel] credit sched on ia64)

[Tristan Gingold <Tristan.Gingold@xxxxxxxx>]

Le Lundi 03 Juillet 2006 06:22, Isaku Yamahata a écrit :
> This patch allows vcpu to move between pcpus.
> I couldn't boot domU on credit scheduler without this patch.
> This patch is only for correctness. This patch isn't efficient.
2 comments:

The obvious question is why not using _dirty_cpumask; but the obvious reason 
is of course performance issues :-)  So I *definitly* agree with your patch.

The patch is not that inefficient: only vcpu migration is inefficent !

> Maybe a consideration on VHPT per pcpu is needed.
> - allocation of region id per domain.
>   Should rid region be allocated per vcpu?
Two issues:
* lack of rids as you noted
* linux assumes rid can be shared: if rid are allocated per vcpu, process 
migration can be expansive.

>   By this, it would be unnecessary to flush when vcpu movement.
>   But I think this isn't very preferable because the size of region id
>   given to vcpu would be too small.
>
> - Currently allocation of VHPT per physical cpus.
>   Allocate VHPT per vcpu like vt-i domain?
Vcpu migration is a big pro for per VHPT vcpu, but NUMA is a cons :-)
>   I think this is preferable, but some measuremeat should back this.

> - other?
One may ask wether or not vcpu migration is interesting wrt NUMA.  I think for 
NUMA machines, vcpu migration must go with memory migration.

Also, note that __cacheline_aligned_in_smp is defined as nothing on xen/ia64.
You'd better either not to use it or define it.

Tristan.

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