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Date: Tue, 27 Sep 2016 13:57:00 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Prarit Bhargava <prarit@redhat.com>
Cc: Borislav Petkov <bp@suse.de>, linux-kernel@vger.kernel.org,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
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        Len Brown <len.brown@intel.com>, Andi Kleen <ak@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>, Juergen Gross <jgross@suse.com>
Subject: Re: [PATCH 0/2 v3] cpu hotplug: Preserve topology directory after
 soft remove event
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On Tue, Sep 27, 2016 at 07:47:56AM -0400, Prarit Bhargava wrote:

> There's a difference between soft remove (via sysfs) and a true hot remove
> operation (where the whole thing is physically removed).  Soft remove only
> results in the processor being made "not available" to the scheduler.

How is it different? We do _ONE_ CPU unplug operation. We do not touch
the thing anymore after that. It _can_ be taken out after that.

Therefore hotplug wipes the topology information and clears the CPU from
relevant bitmasks.

>>From the kernel's POV there really is no distinction.