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Date: Tue, 8 Apr 2025 13:44:25 -0700 (PDT)
From: "Christoph Lameter (Ampere)" <cl@gentwo.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
cc: Sweet Tea Dorminy <sweettea@google.com>, Mateusz Guzik <mjguzik@gmail.com>, 
    linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>, 
    "Paul E. McKenney" <paulmck@kernel.org>, 
    Steven Rostedt <rostedt@goodmis.org>, 
    Masami Hiramatsu <mhiramat@kernel.org>, Dennis Zhou <dennis@kernel.org>, 
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    Lorenzo Stoakes <lorenzo.stoakes@oracle.com>, 
    "Liam R . Howlett" <Liam.Howlett@Oracle.com>, 
    Suren Baghdasaryan <surenb@google.com>, Vlastimil Babka <vbabka@suse.cz>, 
    Christian Brauner <brauner@kernel.org>, 
    Wei Yang <richard.weiyang@gmail.com>, David Hildenbrand <david@redhat.com>, 
    Miaohe Lin <linmiaohe@huawei.com>, Al Viro <viro@zeniv.linux.org.uk>, 
    linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, 
    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, Mathieu Desnoyers wrote:

> Currently percpu_counter_tree_precise_sum_unbiased() iterates on each
> possible cpu, which does not require cpu hotplug integration.

Well that looks like a performance issue if you have a system that can
expand to 8K cpus but currently only has 16 or so online.