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TLBI domains (FEAT_TLBID) is >>> an Arm architecture feature that enables a TLB invalidation to target a subset >>> of CPUs instead of the whole system. It can improve performance on systems with >>> many CPUs. TLBID is not yet part of the Arm Architecture Reference Manual but >>> some of it is described in the latest XML [1]. >>> >>> The goal of this series is to send TLBI commands only to the CPUs where a >>> process has run (i.e. where its page tables have been installed). The last >> >> IIUC, mm_cpumask() is used to store this information on x86 and other >> archs. I see you put this information in tlbid_domains of mm_context_t >> from patch 9, although in the form of tlb id domains. I wonder why not >> make arm64 also update mm_cpumask() like x86 and other archs and derive >> the tlbid domains based on mm_cpumask() and a cpu-to-domain mapping >> (added in patch 7). > > Historically, maintaining mm_cpumask() was a horrible source of contention > when we looked at it in the past. Maybe that's no longer true, but it Do you have a pointer to the cost you have in mind? LLM can only finds some overhead reduction work done by Rik for x86[1][2]. [1] https://lore.kernel.org/all/20180716190337.26133-8-riel@surriel.com/T/#u [2] https://lore.kernel.org/all/20241114152723.1294686-2-riel@surriel.com/ BTW, patch 9 is updating tlbid domains unconditionally. It can be optimized in the same way as Rik did for x86 mm_cpumask(), read the tlbid domain first and only update if CPU is in a new domain. > would be good to see some numbers if we want to start keeping that thing > accurate on arm64. Best Regards, Yan, Zi