Michal Suchánek <msucha...@suse.de> writes: > On Thu, 18 Apr 2019 13:56:56 -0500 > Nathan Lynch <nath...@linux.ibm.com> wrote: > > Hello, > >> Changing cpu <-> node relationships at runtime, as the pseries >> platform code attempts to do for LPM, PRRN, and VPHN is essentially >> unsupported by core subsystems. [1] > > Wasn't there a patch that solves the discrepancy by removing and > re-adding the updated CPUs? > > http://patchwork.ozlabs.org/patch/1051761/
In our testing it seems that changing the result of cpu_to_node() for a given cpu id, even with an intervening offline/online, leads to crashes and assertions in the slab allocator. There have been some ideas floated to sidestep that but I think there are larger issues to consider. Even if changing CPU node assignments were possible to do without destabilizing the system it's not all that useful without updating memory/LMB affinity as well. (VPHN is an exception.) Furthermore I'm not aware of any effort to make the numa/affinity APIs at the system call level account for the possibility that the cpu/mem <-> node relationship could be dynamic. Nor is there any facility for notifying applications of changes. Even if the kernel were to properly support this internally, NUMA-aware applications are the ones that will suffer unless appropriate APIs are provided to them. To me it seems this all needs more careful consideration and work, and much of it should happen outside of this particular arch/platform context.
