Messages in this thread | | | Date | Fri, 1 Sep 2023 14:01:52 -0500 | From | Steve Wahl <> | Subject | Re: [PATCH] x86/platform/uv: Use alternate source for socket to node data |
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On Fri, Sep 01, 2023 at 10:18:20AM -0700, Dave Hansen wrote: > On 8/7/23 07:17, Steve Wahl wrote: > > When nr_cpus is set to a smaller number than actually present, the > > cpu_to_node() mapping information for unused CPUs is not available to > > build_socket_tables(). This results in an incomplete table and will > > later cause use of a -1 value for some array indexing, and eventual > > kernel page faults. > > > > Switch to using the __apicid_to_node array, which still contains all > > the information mapping apicids to nodes, even for CPUs disabled with > > a reduced nr_cpus setting. > > Before, the lookup went: > > CPU => APICID => SOCKET > > But when the CPU wasn't present, there wasn't a way to start this lookup. > > So, instead of looping over all CPUs, looking up their APICIDs and > mapping those to sockets, just take CPUs out of the equation entirely. > > Loop over all APICIDs which are mapped to a valid NUMA node. Then just > extract the socket-id from the APICID. > > Right? > > That seems sane enough. It's also way less code than the previous approach.
Yes. That's it precisely. And, yes, way less code.
Thanks.
--> Steve Wahl
-- Steve Wahl, Hewlett Packard Enterprise
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