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

From: Borislav Petkov
Date: Mon Sep 26 2016 - 07:57:37 EST

On Mon, Sep 26, 2016 at 07:45:37AM -0400, Prarit Bhargava wrote:
> 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.

What does "the location" mean exactly?

> cpupower should still print out all asterisks for down'd threads. It does not
> because the topology directory is incorrectly removed.
> IOW how does userspace know the _location_ of the thread? The topology
> directory no longer exists when the thread is downed, so core_id and
> physical_package_id (both of which would be effectively static) do not exist.
> The whole point of this patchset is to know where the offline'd thread actually is.

What do you mean "where"?

$ echo 0 > /sys/devices/system/cpu/cpu2/online
$ cat /sys/devices/system/cpu/online

So core 2 is right between 1 and 3.

If you need to show the package id, you still iterate over the core
numbers in an increasing order and show '*' for the offlined ones.


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