Re: [RFC,5/7] NUMA hotplug emulator

[Haicheng Li <haicheng.li@linux.intel.com>]

Paul E. McKenney wrote:
> On Fri, May 07, 2010 at 04:11:42PM +0200, Pavel Machek wrote:
>> Hi!
>>
>>> hotplug emulator: Abstract cpu register functions
>>>
>>> Abstract function arch_register_cpu and register_cpu, move the implementation
>>> details to a sub function with prefix "__". 
>>>
>>> each of the sub function has an extra parameter nid, it can be used to register
>>> CPU under a fake NUMA node, it is a reserved interface for cpu hotplug emulation
>>> (CPU PROBE/RELEASE) in x86.
>> I don't get it. CPU hotplug can already be tested using echo 0/1 >
>> online, and that works on 386. How is this different?

"echo 0/1 > online" is logical cpu online/offline.
The emulator intends to emulate physical add/remove of cpus.
They cover different code path.

You can get details of the terms via $KERN_SRC/Documentation/cpu-hotplug.txt.

>> It seems to add some numa magic. Why is it important?

In real world, numa affinity info of the cpus is required for physical cpu hotadd/remove
, which finally affects related data structures and code path. Emulator need the ability
to emulate it.

> My guess is that he wants to test the software surrounding NUMA on a
> non-NUMA (or different-NUMA) machine, perhaps in order to shake out bugs
> before the corresponding hardware is available.

This is one of the purposes. Auto tests and debugging all can get benefits from such emulation.


-haicheng

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