maxcpus behavior in arm64

Rohit Vaswani rvaswani at
Tue May 13 11:56:01 PDT 2014

Hi Catalin,

I notice that the maxcpus behavior is different in arm64 than from how 
arm uses it.
in arm64/kernel/smp.c - in smp_prepare_cpus, maxcpus is used to limit 
the cpu_present_mask.
However in arm/kernel/smp.c - maxcpus is not used as a decision maker to 
set the cpu_preset_mask.

Is this behavior expected and intentionally different in arm and arm64 ?
This also means that in arm64 (unlike arm)- maxcpus cannot be used to 
boot a subset of total cpus with the
option of getting the secondary cores online at a later point from 
userspace using hotplug.
It seems like maxcpus is being treated like nr_cpus in arm64 ?
Please could you help clarify this behavior and help us understand this 

Rohit Vaswani

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