linux-kernel - Re: Topology updates and NUMA-level sched domains

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Message-ID: <20150409223709.GF53918@linux.vnet.ibm.com>
Date:	Thu, 9 Apr 2015 15:37:09 -0700
From:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
To:	Brice Goglin <Brice.Goglin@...ia.fr>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Boqun Feng <boqun.feng@...ux.vnet.ibm.com>,
	Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
	linuxppc-dev@...ts.ozlabs.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Anton Blanchard <anton@...ba.org>
Subject: Re: Topology updates and NUMA-level sched domains

On 08.04.2015 [12:32:01 +0200], Brice Goglin wrote:
> Le 07/04/2015 21:41, Peter Zijlstra a écrit :
> > No, that's very much not the same. Even if it were dealing with hotplug
> > it would still assume the cpu to return to the same node.
> >
> > But mostly people do not even bother to handle hotplug.
> >
> 
> You said userspace assumes the cpu<->node relation is a boot-time fixed
> one, and hotplug breaks this. How do you expect userspace to handle
> hotplug? Is there a convenient way to be notified when a CPU (or memory)
> is unplugged?

There is some mention of "User Space Notification" in cpu-hotplug.txt,
but no idea if it's current.

-Nish

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