Messages in this thread | | | Date | Mon, 21 Sep 2009 17:19:13 -0700 (PDT) | From | David Rientjes <> | Subject | Re: [RFC PATCH 0/3] Fix SLQB on memoryless configurations V2 |
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On Tue, 22 Sep 2009, Benjamin Herrenschmidt wrote:
> So if I understand correctly, we have a problem with both cpu-less and > memory-less nodes. Interesting setups :-) >
I agree with Christoph that we need to resolve the larger kernel issue of memoryless nodes in the kernel and the result of that work will most likely become the basis from which the slqb fixes originate.
I disagree that we need kernel support for memoryless nodes on x86 and probably on all architectures period. "NUMA nodes" will always contain memory by definition and I think hijacking the node abstraction away from representing anything but memory affinity is wrong in the interest of a long-term maintainable kernel and will continue to cause issues such as this in other subsystems.
I do understand the asymmetries of these machines, including the ppc that is triggering this particular hang with slqb. But I believe the support can be implemented in a different way: I would offer an alternative representation based entirely on node distances. This would isolate each region of memory that has varying affinity to cpus, pci busses, etc., into nodes and then report a distance, whether local or remote, to other nodes much in the way the ACPI specification does with proximity domains.
Using node distances instead of memoryless nodes would still be able to represent all asymmetric machines that currently benefit from the support by binding devices to memory regions to which they have the closest affinity and then reporting relative distances to other nodes via node_distance().
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