linux-kernel - Re: [8/8,v3] NUMA Hotplug Emulator: documentation

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Date:	Tue, 23 Nov 2010 07:23:02 +0800
From:	Shaohui Zheng <shaohui.zheng@...el.com>
To:	Américo Wang <xiyou.wangcong@...il.com>
Cc:	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, haicheng.li@...ux.intel.com,
	lethal@...ux-sh.org, ak@...ux.intel.com,
	shaohui.zheng@...ux.intel.com, Haicheng Li <haicheng.li@...el.com>
Subject: Re: [8/8,v3] NUMA Hotplug Emulator: documentation

On Tue, Nov 23, 2010 at 12:04:12AM +0800, Américo Wang wrote:
> On Mon, Nov 22, 2010 at 07:33:51AM +0800, Shaohui Zheng wrote:
> >On Sun, Nov 21, 2010 at 11:03:45PM +0800, Américo Wang wrote:
> >> 
> >> >From your documentation above, it looks like you are trying
> >> to move one CPU between nodes?
> >Yes, you are correct. With cpu probe/release interface, you can hot-remove a
> >CPU from a node, and hot-add it to another node.
> 
> 
> Can I also move the CPU to another node _after_ it is hot-added?
> Or I have to hot-remove it first and then hot-add it again?
of course you can. you can hot-remove it via cpu/release interface, and then hot-add 
it by cpu/probe interface.

With the cpu probe/reelase interface, we can design some stress test cases to hot add/remove
cpu by script.
> 
> >> 
> >> >+	cpu_hpe=on/off
> >> >+		Enable/disable cpu hotplug emulation with software method. when cpu_hpe=on,
> >> >+		sysfs provides probe/release interface to hot add/remove cpu dynamically.
> >> >+		this option is disabled in default.
> >> >+			
> >> 
> >> Why not just a CONFIG? IOW, why do we need to make another boot
> >> parameter for this?
> >Only the developer or QA will use the emulator, we did not want to change the
> >default action for common user who does not care the hotplug emulator, so we
> >use a kernel parameter as a switch. The common user is not aware the existence
> >of the emulator.
> >
> 
> I think it is also useful to other Linux users, e.g. after I
> boot with "maxcpus=1", I can still bring the rest 3 CPU's
> back without reboot.
You understand it very well. the probe/release on ppc is already implemented,
but for x86, it is a feature missing, so we finished it with these patches.

> 
> Thanks.
> 
> -- 
> Live like a child, think like the god.
>  

-- 
Thanks & Regards,
Shaohui

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