Re: [Xen-ia64-devel] RFC: ptc.ga implementation for SMP-g

[Tristan Gingold <Tristan.Gingold@xxxxxxxx>]

Le Mardi 04 Avril 2006 21:46, Magenheimer, Dan (HP Labs Fort Collins) a écrit
[...]
> I think ptc.ga needs to execute as a "transaction", that is,
> it is not complete until all other processors' translations
> have been purged.  If not, consider (in the above):
>
> 4.5. vcpu2 doesn't trap to the hypervisor for a very long time
>      and continues to use the unpurged translation, while vcpu1
>      assumes the translation has been successfully purged and
>      sets up a new translation and assumes that vcpu2 will "miss"
>      and use the new translation.
I agree.

But if vcpu1 has to wait, this can result in a dead-lock if we do 
busy-waiting:
vcpu1 of dom1 on LP1 waits for vcpu2 of dom1 on LP2,
while vcpu2 of dom2 on LP2 waits for vcpu1 of dom2 on LP2.

Tristan.



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