linux-kernel - Re: [PATCH v2 2/2] Do not change worker's running cpu in cmci

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Message-ID: <5085F33B.501@cn.fujitsu.com>
Date:	Tue, 23 Oct 2012 09:30:35 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Borislav Petkov <bp@...en8.de>, "Luck, Tony" <tony.luck@...el.com>,
	Borislav Petkov <bp@...64.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"miaox@...fujitsu.com" <miaox@...fujitsu.com>,
	"laijs@...fujitsu.com" <laijs@...fujitsu.com>,
	"wency@...fujitsu.com" <wency@...fujitsu.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] Do not change worker's running cpu in cmci_rediscover().

On 10/22/2012 06:18 PM, Borislav Petkov wrote:
> On Mon, Oct 22, 2012 at 11:33:16AM +0800, Tang Chen wrote:
>> I have 2 nodes, node0 and node1. node1 could be hotpluged.
>> node0 has cpu0 ~ cpu15, node1 has cpu16 ~ cpu31.
>>
>> I online all the cpus on node1, and hot-remove node1 directly.
>
> Hold on, I need to ask here: you soft-online all cores on node1 and
> *then* you *hot* *remove* it? So with all cores online you physically
> take out the processor from the socket? Am I reading this correctly?

Hi Borislav,

No, it's not like that. I'm sorry to make you confused.

Firstly, let me do a little explanation here. :)

I was doing ACPI based hotplug. In a container device, it contains
cpus and memories and so on. I didn't physically remove cpus from
hardware. I emulated a SCI with my own test module, and the
container_notify_cb() was called, and it recursively remove all the
sub-devices.

The "remove" here doesn't mean "taking it away". And of course, when
the "remove" is done, you can physically take the whole system board
away.

Please refer to this url:
http://www.spinics.net/lists/linux-pci/msg17651.html
This is the module we are doing the SCI emulation.

In summary, the hotplug process could be like the following:

hot-add(SCI) -> online(softly) -> device working -> offline(softly) -> 
hot-remove(SCI)

Secondly, in kernel, before a container device is removed, all its
sub-devices will be offlined and removed first. So I have all the cpus
online, and hot-remove a container(which I think is a node, maybe not)
directly. This operation has no problem, I think.

Maybe I should not say container as a node. :)

And again, sorry for the confusion.

Thanks. :)

>
> Thanks.
>

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