Re: [PATCH 0/2 v3] cpu hotplug: Preserve topology directory after soft remove event

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 0/2 v3] cpu hotplug: Preserve topology directory after soft remove event
Date	2016-09-26 14:10 +0200
Message-ID	<slCTo-3FS-11@gated-at.bofh.it> (permalink)
References	(2 earlier) <sjPUK-17j-19@gated-at.bofh.it> <sjQnM-1xc-25@gated-at.bofh.it> <skaPw-5PF-41@gated-at.bofh.it> <skb8S-6eS-11@gated-at.bofh.it> <slCA2-3kx-5@gated-at.bofh.it>
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On Mon, Sep 26, 2016 at 07:45:37AM -0400, Prarit Bhargava wrote:
> > But then code which reads those will have to *know* that those cores are
> > offline - otherwise it would be confused by what it is reading there.
> 
> When offline, /sys/devices/system/cpuX/cpu/online is 0.  The problem is that
> when online is 0, topology disappears so there is no way to determine _the
> location_ of the offline'd thread.

As far as all that code is concerned, that CPU doesn't even have a
location anymore.

While there might be some distinction between hotplug and physical
hotplug on the user API side (I really wouldn't know), there isn't on
the kernel side.

Once you unplug a CPU, its _gone_. There isn't another hotplug operation
once you really take the CPU out.

Offline means out gone, vamoosh.

And it doesn't make sense to talk about the location of a resource
that's not there.

Thread

Re: [PATCH 0/2 v3] cpu hotplug: Preserve topology directory after  soft remove event Prarit Bhargava <prarit@redhat.com> - 2016-09-26 13:50 +0200
  Re: [PATCH 0/2 v3] cpu hotplug: Preserve topology directory after  soft remove event Borislav Petkov <bp@suse.de> - 2016-09-26 14:00 +0200
    Re: [PATCH 0/2 v3] cpu hotplug: Preserve topology directory after  soft remove event Prarit Bhargava <prarit@redhat.com> - 2016-09-27 13:50 +0200
      Re: [PATCH 0/2 v3] cpu hotplug: Preserve topology directory after  soft remove event Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-09-27 16:00 +0200
        Re: [PATCH 0/2 v3] cpu hotplug: Preserve topology directory after  soft remove event Prarit Bhargava <prarit@redhat.com> - 2016-09-27 17:30 +0200
          Re: [PATCH 0/2 v3] cpu hotplug: Preserve topology directory after  soft remove event Borislav Petkov <bp@suse.de> - 2016-09-28 07:10 +0200
          Re: [PATCH 0/2 v3] cpu hotplug: Preserve topology directory after  soft remove event Peter Zijlstra <peterz@infradead.org> - 2016-09-28 08:50 +0200
            Re: [PATCH 0/2 v3] cpu hotplug: Preserve topology directory after  soft remove event Prarit Bhargava <prarit@redhat.com> - 2016-09-28 12:10 +0200
      Re: [PATCH 0/2 v3] cpu hotplug: Preserve topology directory after  soft remove event Borislav Petkov <bp@suse.de> - 2016-09-28 07:10 +0200
  Re: [PATCH 0/2 v3] cpu hotplug: Preserve topology directory after  soft remove event Peter Zijlstra <peterz@infradead.org> - 2016-09-26 14:10 +0200
    Re: [PATCH 0/2 v3] cpu hotplug: Preserve topology directory after  soft remove event Prarit Bhargava <prarit@redhat.com> - 2016-09-27 13:50 +0200
      Re: [PATCH 0/2 v3] cpu hotplug: Preserve topology directory after  soft remove event Peter Zijlstra <peterz@infradead.org> - 2016-09-27 14:00 +0200

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