Re: Off topic: Numactl "distance" wrong

[Andi Kleen <andi@firstfloor.org>]

Yinghai Lu <yhlu.kernel@gmail.com> writes:

> On Fri, Apr 3, 2009 at 2:43 PM, David Rientjes <rientjes@google.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.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only.