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McKenney" cc: Mathieu Desnoyers , Sweet Tea Dorminy , Mateusz Guzik , linux-kernel@vger.kernel.org, Andrew Morton , Steven Rostedt , Masami Hiramatsu , Dennis Zhou , Tejun Heo , Martin Liu , David Rientjes , christian.koenig@amd.com, Shakeel Butt , Johannes Weiner , Lorenzo Stoakes , "Liam R . Howlett" , Suren Baghdasaryan , Vlastimil Babka , Christian Brauner , Wei Yang , David Hildenbrand , Miaohe Lin , Al Viro , linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, Yu Zhao , Roman Gushchin , Matthew Wilcox Subject: Re: [RFC PATCH v2] Introduce Hierarchical Per-CPU Counters In-Reply-To: <9f42144b-dca9-41b0-a80b-2e402cb5ab98@paulmck-laptop> Message-ID: <8897b4e1-b5ba-807d-7bc4-5a6080a93462@gentwo.org> References: <20250408160508.991738-1-mathieu.desnoyers@efficios.com> <9f42144b-dca9-41b0-a80b-2e402cb5ab98@paulmck-laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 456CE40010 X-Stat-Signature: caanfbtsqyymqc73n68pihwsx3ikdifb X-Rspam-User: X-HE-Tag: 1744147320-324277 X-HE-Meta: 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 bEbpTZEf 1gqpRQGJ+r9cAn+WNwgk+mMt2xUH1JuMLuVC/Xz1Ml2jxBVnhbaS6+2SPc/9Ga/YS1/r7PXg9CD3MQRXLv1iDXKJfhPhDBaQn3hw5HvgNQBFwDWBInZ4VszrpCbjGsTgTTUtsuHRtaQ92YBnTDDDvvCNBn+sUZfugUkAVk/x4tJyqxEXHkZXQiEbLeQRj9bgqb7/GRTli9uJNLO5xtyICxxq7ehs0OP4xoYHD2ZRxQFnYfwShY3rCqHpMdt34nAy7hYrG3Hvoep21fsnwfgZSLyNt2Cv4N7U3FlfbzMw7YNY0jsy2C8q9czehNStm//DN1M4o X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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....