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

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Date:	Wed, 1 Apr 2015 11:55:11 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>
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 2015/04/01 0:28, Tejun Heo wrote:
> Hello, Kamezawa.
>
> On Tue, Mar 31, 2015 at 03:09:05PM +0900, Kamezawa Hiroyuki wrote:
>> But this may be considered as API change for most hot-add users.
>
> Hmm... Why would it be?  What can that possibly break?
>

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.

>> So, for now, I vote for detemining ids at online but record it is a good way.
>
> If we know the information during boot, let's please do it at boot
> time by all means.

I basically agree. Just thinking influence of this small imcompatibility of forcing
ideal way because of my standing point.

Thanks,
-Kame

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