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

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Date:	Mon, 30 Mar 2015 17:49:49 +0800
From:	Gu Zheng <guz.fnst@...fujitsu.com>
To:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	Tejun Heo <tj@...nel.org>, <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

Hi Kame-san,

On 03/27/2015 12:42 AM, Kamezawa Hiroyuki wrote:

> 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.

Could you explain more?

Regards,
Gu

> 
> 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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