linux-kernel - Re: [PATCH V6 1/2] powerpc/hotplug: Ensure enough nodes avail for operations

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Message-Id: <75a86b88-ae0c-93c1-dade-85d5e8315610@linux.vnet.ibm.com>
Date:   Wed, 21 Jun 2017 09:24:59 -0500
From:   Michael Bringmann <mwb@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        David Gibson <david@...son.dropbear.id.au>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        John Allen <jallen@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Bharata B Rao <bharata@...ux.vnet.ibm.com>,
        Shailendra Singh <shailendras@...dia.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Rashmica Gupta <rashmicy@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Tyrel Datwyler <tyreld@...ux.vnet.ibm.com>,
        Michael Bringmann from Kernel Team <mbringm@...ibm.com>,
        Nathan Fontenot <nfont@...ux.vnet.ibm.com>
Subject: Re: [PATCH V6 1/2] powerpc/hotplug: Ensure enough nodes avail for
 operations



On 06/21/2017 04:52 AM, Michael Ellerman wrote:
> Michael Bringmann <mwb@...ux.vnet.ibm.com> writes:
> 
>> powerpc/hotplug: On systems like PowerPC which allow 'hot-add' of CPU
>> or memory resources, it may occur that the new resources are to be
>> inserted into nodes that were not used for these resources at bootup.
>> In the kernel, any node that is used must be defined and initialized
>> at boot.  In order to meet both needs, this patch adds a new kernel
>> command line option (numnodes=<int>) for use by the PowerPC architecture-
> 
> Sorry, that's a hack.

It is an intermediate step pending the provision of the firmware properties
under discussion that were mentioned by Nathan Fontenot last week.

> I thought you were going to use firmware properties to find the set of
> possible nodes. Did that not work?

Inference based on the current set of firmware properties for associativity
is insufficient.  That is partly the reason for the properties mentioned by
Nathan last week.  The current firmware properties only cover what is known
at boot time.  They do not cover expansions from DLPAR / hot-add operations
which can add up to everything else on the system.

> cheers

Regards,

-- 
Michael W. Bringmann
Linux Technology Center
IBM Corporation
Tie-Line  363-5196
External: (512) 286-5196
Cell:       (512) 466-0650
mwb@...ux.vnet.ibm.com