linux-kernel - Re: Off topic: Numactl "distance" wrong

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Date:	Fri, 3 Apr 2009 15:15:48 -0700
From:	Yinghai Lu <yhlu.kernel@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	David Rientjes <rientjes@...gle.com>,
	Chris Worley <worleys@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: Off topic: Numactl "distance" wrong

On Fri, Apr 3, 2009 at 2:55 PM, Andi Kleen <andi@...stfloor.org> wrote:
> Yinghai Lu <yhlu.kernel@...il.com> writes:
>
>> On Fri, Apr 3, 2009 at 2:43 PM, David Rientjes <rientjes@...gle.com> wrote:
>>>
>>> Yinghai, can you elaborate on exactly what type of interface you can
>>> imagine for modifying the distance for nodes through sysfs?  It seems like
>>> you'd have to report the entire physical topology in one write, for which
>>> we currently don't have an interface for beyond pxms, instead of per-node
>>> distances to remote nodes.
>>
>> acpi_numa_slit_init() in srat_64.c will have one copy (called
>> acpi_slit) of SLIT, if there is SLIT from ACPI.
>>
>> so if numa is enabled, could expose that acpi_slit via sysfs for the
>> user to update it.
>
> That's not enough. You would need to redo all the zone fallback tables
> in the VM that are initialized based on topology, do new scheduler
> topologies and all kind of other stuff.
>
> Besides I don't know any user space software which actually does anything
> with the distances. The kernel does, but for it it doesn't make much difference
> on smaller systems.

how the cpu and memory hotplug works when it could change kind of topology?
sched: wonder if arch_reinit_sched_domains() is used to
rebuild_sched_domains() it will call node_distance()

or ACPI asl code could update SLIT table , and let os use slit table.

YH
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