Re: [Xen-devel] [PATCH] linux: don't bring up CPUs that can never be used

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>> I'm a little bit wary of the second hunk. Although it's probably
okay,
>> is it
>>> actually required? Looks like the first hunk is what fixes the
issue.
>> 
>> It's probably not strictly required, but sill better than iterating
>> over NR_CPUS, as
>> that is what mainline is in the process of phasing out. The only
>> difference I can
>> see to the results of the original code is that for cpu 0 the two
array
>> members
>> now also get (re-)initialized here - but the value stored should be
the
>> same as
>> may have been stored earlier.
>
>If it's true that those maps only get interrogated for CPUs in the
>cpu_online_map, could we remove that loop altogether? We initialise
the map
>entries for CPUs as they're brought online in __cpu_up(): should that
>suffice?

I think considering cpu_possible_map/cpu_present_map would be safer
here,
which is why I made the loop run over cpu_present_map. __cpu_up
wouldn't
be sufficient for setting this up then. I am, however, not sure whether
these
maps ever get accessed for non-online CPUs, so your suggestion might
well
work.

Jan

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