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

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Date:	Tue, 31 Mar 2015 23:02:42 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Gu Zheng <guz.fnst@...fujitsu.com>, linux-kernel@...r.kernel.org,
	laijs@...fujitsu.com, isimatu.yasuaki@...fujitsu.com,
	tangchen@...fujitsu.com, izumi.taku@...fujitsu.com
Subject: Re: [PATCH 0/2] workqueue: fix a bug when numa mapping is changed

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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