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

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Date:	Fri, 27 Mar 2015 01:42:26 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>, Gu Zheng <guz.fnst@...fujitsu.com>
CC:	<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 2015/03/27 0:18, Tejun Heo wrote:
> Hello,
>
> On Thu, Mar 26, 2015 at 01:04:00PM +0800, Gu Zheng wrote:
>> wq generates the numa affinity (pool->node) for all the possible cpu's
>> per cpu workqueue at init stage, that means the affinity of currently un-present
>> ones' may be incorrect, so we need to update the pool->node for the new added cpu
>> to the correct node when preparing online, otherwise it will try to create worker
>> on invalid node if node hotplug occurred.
>
> If the mapping is gonna be static once the cpus show up, any chance we
> can initialize that for all possible cpus during boot?
>

I think the kernel can define all possible

  cpuid <-> lapicid <-> pxm <-> nodeid

mapping at boot with using firmware table information.

One concern is current x86 logic for memory-less node v.s. memory hotplug.
(as I explained before)

My idea is
   step1. build all possible mapping at boot cpuid <-> apicid <-> pxm <-> node id at boot.

But this may be overwritten by x86's memory less node logic. So,
   step2. check node is online or not before calling kmalloc. If offline, use -1.
          rather than updating workqueue's attribute.

Thanks,
-Kame

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