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With NUMA emulation, it's possible for a single cpu to be bound to multiple nodes since more than one may have affinity if allocated on a physical node that is local to the cpu. APIC ids must therefore be mapped to the lowest node ids to maintain generic kernel use of functions such as cpu_to_node() that determine device affinity. For example, if a device has proximity to physical node 1, for instance, and a cpu happens to be mapped to a higher emulated node id 8, the proximity may not be correctly determined by comparison in generic code even though the cpu may be truly local and allocated on physical node 1. When this happens, the true topology of the machine isn't accurately represented in the emulated environment; although this isn't critical to the system's uptime, any generic code that is NUMA aware benefits from the physical topology being accurately represented. This can affect any system that maps multiple APIC ids to a single node and is booted with numa=fake=N where N is greater than the number of physical nodes. Signed-off-by: David Rientjes <rientjes@google.com> Cc: Yinghai Lu <yinghai@kernel.org> Cc: Suresh Siddha <suresh.b.siddha@intel.com> LKML-Reference: <alpine.DEB.2.00.1005060224140.19473@chino.kir.corp.google.com> Signed-off-by: Ingo Molnar <mingo@elte.hu> |
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