linux-kernel - Re: [PATCH v3 0/5] Make cpuid <-> nodeid mapping persistent.

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Date:	Tue, 24 Nov 2015 15:13:28 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>
CC:	<cl@...ux.com>, <jiang.liu@...ux.intel.com>,
	<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>, <x86@...nel.org>,
	<linux-acpi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>
Subject: Re: [PATCH v3 0/5] Make cpuid <-> nodeid mapping persistent.


On 11/24/2015 06:04 AM, Tejun Heo wrote:
> Hello,
>
> On Thu, Nov 19, 2015 at 12:22:10PM +0800, Tang Chen wrote:
>> [Solution]
>>
>> There are four mappings in the kernel:
>> 1. nodeid (logical node id)   <->   pxm
>> 2. apicid (physical cpu id)   <->   nodeid
>> 3. cpuid (logical cpu id)     <->   apicid
>> 4. cpuid (logical cpu id)     <->   nodeid
>>
>> 1. pxm (proximity domain) is provided by ACPI firmware in SRAT, and nodeid <-> pxm
>>     mapping is setup at boot time. This mapping is persistent, won't change.
>>
>> 2. apicid <-> nodeid mapping is setup using info in 1. The mapping is setup at boot
>>     time and CPU hotadd time, and cleared at CPU hotremove time. This mapping is also
>>     persistent.
>>
>> 3. cpuid <-> apicid mapping is setup at boot time and CPU hotadd time. cpuid is
>>     allocated, lower ids first, and released at CPU hotremove time, reused for other
>>     hotadded CPUs. So this mapping is not persistent.
>>
>> 4. cpuid <-> nodeid mapping is also setup at boot time and CPU hotadd time, and
>>     cleared at CPU hotremove time. As a result of 3, this mapping is not persistent.
>>
>> To fix this problem, we establish cpuid <-> nodeid mapping for all the possible
>> cpus at boot time, and make it persistent. And according to init_cpu_to_node(),
>> cpuid <-> nodeid mapping is based on apicid <-> nodeid mapping and cpuid <-> apicid
>> mapping. So the key point is obtaining all cpus' apicid.
> I don't know much about acpi so can't actually review the patches but
> the overall approach looks good to me.

Thank you, TJ. Will test it recently.

>
> Thanks.
>


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