linux-kernel - RE: [PATCH v4 0/7] x86: BSP or CPU0 online/offline

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Date:	Thu, 15 Dec 2011 10:38:20 -0800
From:	"Yu, Fenghua" <fenghua.yu@...el.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	H Peter Anvin <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Luck, Tony" <tony.luck@...el.com>,
	"Van De Ven, Arjan" <arjan.van.de.ven@...el.com>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	"Brown, Len" <len.brown@...el.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-pm <linux-pm@...r.kernel.org>, x86 <x86@...nel.org>
Subject: RE: [PATCH v4 0/7] x86: BSP or CPU0 online/offline

> We need a debug feature for this: CONFIG_DEBUG_BOOT_CPU_OFF=y or
> such (disabled by default): this feature would offline the boot
> CPU as soon as possible, and boot up userspace with the boot CPU
> offlined.

I would think the earliest time when CPU0 can be offline is right after do_initcalls() because do_initcalls() installs some cpu hotplug notifier.

But this will change generic code (e.g. add arch hook in init/main.c or add a new initcall level which is after level 7s).

Another way is to offline CPU0 (or any CPU) in /etc/rc.local. By this way, we don't change kernel. And this is safe, but a bit later than in kernel.

Any comment?

Thanks.

-Fenghua
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