linux-kernel - Re: [PATCH v7 0/5] Make cpuid <-> nodeid mapping persistent

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Message-ID: <5742AAF6.3060901@cn.fujitsu.com>
Date:	Mon, 23 May 2016 15:02:14 +0800
From:	Zhu Guihua <zhugh.fnst@...fujitsu.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	<cl@...ux.com>, <tj@...nel.org>, <mika.j.penttila@...il.com>,
	<mingo@...hat.com>, <akpm@...ux-foundation.org>,
	<rjw@...ysocki.net>, <hpa@...or.com>, <yasu.isimatu@...il.com>,
	<isimatu.yasuaki@...fujitsu.com>, <kamezawa.hiroyu@...fujitsu.com>,
	<izumi.taku@...fujitsu.com>, <gongzhaogang@...pur.com>,
	<len.brown@...el.com>, <lenb@...nel.org>, <tglx@...utronix.de>,
	<chen.tang@...ystack.cn>, <rafael@...nel.org>, <x86@...nel.org>,
	<linux-acpi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>
Subject: Re: [PATCH v7 0/5] Make cpuid <-> nodeid mapping persistent

Hi,

On 05/19/2016 10:46 PM, Peter Zijlstra wrote:
> On Thu, May 19, 2016 at 06:39:41PM +0800, Zhu Guihua wrote:
>> [Problem]
>>
>> cpuid <-> nodeid mapping is firstly established at boot time. And workqueue caches
>> the mapping in wq_numa_possible_cpumask in wq_numa_init() at boot time.
>>
>> When doing node online/offline, cpuid <-> nodeid mapping is established/destroyed,
>> which means, cpuid <-> nodeid mapping will change if node hotplug happens. But
>> workqueue does not update wq_numa_possible_cpumask.
> So why are you not fixing up wq_numa_possible_cpumask instead? That
> seems the far easier solution.

We tried to do that. You can see our patch at
http://www.gossamer-threads.com/lists/linux/kernel/2116748

But maintainer thought, we should establish persistent cpuid<->nodeid 
relationship,
there is no need to change the map.

Cc TJ,
Could we return to workqueue to fix this?

Thanks,
Zhu

> Do all the other archs that support NUMA and HOTPLUG have the mapping
> stable, or will you now go fix each and every one of them?
>
>
> .
>