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From: "Yu, Fenghua" <fenghua.yu@intel.com>
To: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
CC: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
        H Peter Anvin <hpa@zytor.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Mallick, Asit K" <asit.k.mallick@intel.com>,
        "Luck, Tony" <tony.luck@intel.com>,
        Arjan Dan De Ven <arjan@linux.intel.com>,
        "Siddha, Suresh B" <suresh.b.siddha@intel.com>,
        "Brown, Len" <len.brown@intel.com>,
        Randy Dunlap <rdunlap@xenotime.net>,
        Chen Gong <gong.chen@linux.intel.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-pm <linux-pm@vger.kernel.org>, x86 <x86@kernel.org>
Subject: RE: [PATCH v9 12/12] x86, topology: Debug CPU00 hotplug
Thread-Topic: [PATCH v9 12/12] x86, topology: Debug CPU00 hotplug
Thread-Index: AQHNqJmgIQc5pNFEs0GDL/Fd3/WvSJe8GfWAgACJoVA=
Date: Wed, 17 Oct 2012 00:06:12 +0000
Message-ID: <3E5A0FA7E9CA944F9D5414FEC6C7122030B196BC@ORSMSX105.amr.corp.intel.com>
References: <1350058189-6769-1-git-send-email-fenghua.yu@intel.com>
 <1350058189-6769-13-git-send-email-fenghua.yu@intel.com>
 <507D1F2F.1010006@linux.vnet.ibm.com>
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> > +#ifdef CONFIG_DEBUG_HOTPLUG_CPU0
 > +	case PM_RESTORE_PREPARE:
> > +		/*
> > +		 * When system resumes from hibernation, online CPU0
> because
> > +		 * 1. it's required for resume and
> > +		 * 2. the CPU was online before hibernation
> > +		 */
> > +		if (!cpu_online(0))
> > +			_debug_hotplug_cpu(0, 1);
> 
> This won't work. CPU hotplug is disabled by cpu_hotplug_pm_callback()
> during
> PM_HIBERNATION_PREPARE and is enabled back only during
> PM_POST_HIBERNATION.
> 
> So calls to cpu_up() or cpu_down() will fail in the meantime.

The code works just fine.

You are talking about hibernation/suspend phase. This piece of
code is all about restore phase. Of course you can call cpu_up()
and cpu_down() during restore phase.

So there is no problem here.

Thanks.

-Fenghua

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