Re: [PATCH 0/2] workqueue: fix a bug when numa mapping is changed

[Tejun Heo]

On Wed, Apr 01, 2015 at 11:55:11AM +0900, Kamezawa Hiroyuki wrote:
> Now, hot-added cpus will have the lowest free cpu id.
> 
> Because of this, in most of systems which has only cpu-hot-add, cpu-ids are always
> contiguous even after cpu hot add.
> In enterprise, this would be considered as imcompatibility.
> 
> determining cpuid <-> lapicid at boot will make cpuids sparse. That may corrupt
> exisiting script or configuration/resource management software.

Ugh... so, cpu number allocation on hot-add is part of userland
interface that we're locked into?  Tying hotplug and id allocation
order together usually isn't a good idea.  What if the cpu up fails
while running the notifiers?  The ID is already allocated and the next
cpu being brought up will be after a hole anyway.  Is this even
actually gonna affect userland?

-- 
tejun
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