Xen devel - Apr 2006 - RE: [PATCH]Check the values of MAX_VIRT_CPUS and NR_CPUSfor SMP

>From: Tristan Gingold [mailto:Tristan.Gingold@bull.net]
>Sent: 2006年4月21日 15:26
>> >
>> >See how we solve this on x86 near the top of do_boot_cpu() in
>> >arch/x86/smpboot.c. Essentially we allocate extra idle domains on
>> >demand to give us enough idle vcpus for one per physical cpu.
>> >
>> >  -- Keir
>>
>> Yes, that''s the same story on ia64 where we also allocate idle
>> vcpu at do_boot_cpu(). That''s why I''m not sure the
real cause
>> for Atsushi''s issue.
>No, we don''t create extra domains.  Therefore it there are more
CPUs
>than
>VCPUs, something goes wrong...
>
Yes, there''s only one idle domain now. However I''m not sure 
why something will go wrong when NR_CPUS > MAX_VIRT_CPUS. 
As long as you want to wake up an AP, you have to go through 
do_boot_cpu where idle_vcpu will be created. The only drawback is 
that some physical cpus will not be waken up by "max_cpus = 
MAX_VIRT_CPUS" you mentioned in another thread. That needs to 
be fixed which however shouldn''t crash anything since uninitialized 
cpus won''t be used.

Thanks,
Kevin

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Le Vendredi 21 Avril 2006 09:28, Tian, Kevin a écrit :
> From: Tristan Gingold [mailto:Tristan.Gingold@bull.net]
>
> >Sent: 2006年4月21日 15:26
> >
> >> >See how we solve this on x86 near the top of do_boot_cpu() in
> >> >arch/x86/smpboot.c. Essentially we allocate extra idle domains
on
> >> >demand to give us enough idle vcpus for one per physical cpu.
> >> >
> >> >  -- Keir
> >>
> >> Yes, that''s the same story on ia64 where we also allocate
idle
> >> vcpu at do_boot_cpu(). That''s why I''m not sure
the real cause
> >> for Atsushi''s issue.
> >
> >No, we don''t create extra domains.  Therefore it there are
more CPUs
> >than
> >VCPUs, something goes wrong...
>
> Yes, there''s only one idle domain now. However I''m not
sure
> why something will go wrong when NR_CPUS > MAX_VIRT_CPUS.
bvt has per VCPU data.  if #VCPU > #MAX_VIRT_CPUS, bvt reads/writes beyond
the
bounds!

Tristan.



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