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become: >>>> INC VIRTUAL_BASE + percpu_variable_offset >>>> >>>> In order to do that we need to have the same virtual address mapped >>>> differently for each processor. This means we need different page >>>> tables for each processor. These page tables >>>> can map almost all of the address space in the same way. The only area >>>> that will be special is the area starting at VIRTUAL_BASE. >>> This is an interesting idea. I'm keen to be involved in discussions. >>> >>> My immediate concern is that this would not be compatible with FEAT_TTCNP, which >>> allows multiple PEs (ARM speak for CPU) to share a TLB - e.g. for SMT. I'm not >>> sure if that would be the end of the world; the perf numbers below are >>> compelling. I'll defer to others' opions on that. >> Thank you for involving the discussion. The concern is definitely >> valid. The shared TLB sounds like a microarchitecture feature or >> design choice. AmpereOne supports CNP, but doesn't share TLB. As long >> as it doesn't generate TLB conflict abort, shared TLB should be fine, >> but may suffer from frequent TLB invalidation. Anyway I think it >> should be solvable. We can make percpu page table opt-in if the >> machines can handle TLB conflict, just like what we did for >> bbml2_noabort. > It's not about TLB conflicts but rather using the wrong translation for > a per-CPU variable with CnP. Ah, yes. It may be just a simple TLB hit for the other CPU due to the same virtual address is used if TLB is shared.