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

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

Oops, seems that flush is inevitable as your example for percpu area...

Thanks,
Kevin

>From: Tian, Kevin
>Sent: 2006年7月4日 10:13
>
>>From: Isaku Yamahata
>>Sent: 2006年7月3日 12:22
>>
>>Maybe a consideration on VHPT per pcpu is needed.
>>- allocation of region id per domain.
>>  Should rid region be allocated per vcpu?
>
>If guest allocates RID globally like Linux, per vcpu rid region is difficult
>to work. If the higher 6 bit is used as vcpu_id instead of domain_id,
>the number of allowed domains reduce. If you use more highest bits,
>the minimal 18bits can't be satisfied and then you need non-linear
>mapping between mrid->vrid. Also the purge like Anthony mentioned
>will be a big issue.
>
>>
>>- other?
>
>Just found a bad performance effect under some condition. For
>example, say one domain with 2 vcpus both running on same LP (no
>other domains). You can easily find that vhpt/tlb flush is issued at each
>context switch between these 2 vcpus even without migration.
>      Last_vcpu_id     current vcpu id       result
>           Invalid            0               N/A
>              0              1               whole tlb/vhpt flush
>              1              0               whole tlb/vhpt flush
>              ...
>
>Thanks,
>Kevin
>
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