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Date: Tue, 8 Apr 2025 14:21:59 -0700 (PDT)
From: "Christoph Lameter (Ampere)" <cl@gentwo.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, 
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    Yu Zhao <yuzhao@google.com>, Roman Gushchin <roman.gushchin@linux.dev>, 
    Matthew Wilcox <willy@infradead.org>
Subject: Re: [RFC PATCH v2] Introduce Hierarchical Per-CPU Counters
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On Tue, 8 Apr 2025, Paul E. McKenney wrote:

> RCU handles this by iterating from zero to nr_cpu_ids, which is set during
> early boot.  It also builds its tree-shaped data structures during early
> boot based on nr_cpu_ids.

nr_cpu_ids is better but there are funky things like the default bios of a
major server vendor indicating 256 or so possible cpus although only 2
were installed. Thus nr_cpu_id is 256. Presumably some hardware
configurations can support onlining 256 cpus....