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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49d26c39086sm240080175e9.10.2026.09.12.14.14.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 12 Sep 2026 14:14:01 -0700 (PDT) Date: Sat, 12 Sep 2026 22:14:00 +0100 From: David Laight To: "Paul E. McKenney" Cc: Alexei Starovoitov , Josef Bacik , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Boqun Feng , Thomas Gleixner , Peter Zijlstra , Steven Rostedt , Masami Hiramatsu , Mark Rutland , Jiri Olsa , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , x86@kernel.org, Catalin Marinas , Will Deacon , Puranjay Mohan , Xu Kuohai , Andy Lutomirski , Josh Triplett , Uladzislau Rezki , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Juergen Gross , Luis Chamberlain , Ihor Solodrai , linux-kernel@vger.kernel.org, rcu@vger.kernel.org, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-arm-kernel@lists.infradead.org, xen-devel@lists.xenproject.org Subject: Re: [PATCH RFC v2 08/15] bpf, x86: Maintain Tasks RCU trampoline nesting in the BPF trampoline Message-ID: <20260912221400.4045198b@pumpkin> In-Reply-To: <8c51a669-eb6b-455b-a829-b537da5209f8@paulmck-laptop> References: <20260911-b4-rcu-tasks-preempt-qs-v2-0-eaaa61ed2da4@toxicpanda.com> <20260911-b4-rcu-tasks-preempt-qs-v2-8-eaaa61ed2da4@toxicpanda.com> <14cb8a91-497d-49f5-aa20-c6cb8b9a27fc@paulmck-laptop> <8c51a669-eb6b-455b-a829-b537da5209f8@paulmck-laptop> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Sat, 12 Sep 2026 11:03:34 -0700 "Paul E. McKenney" wrote: > In the old kernels, yes, we have current->trc_reader_nesting++. > In the newer kernels, Tasks Trace RCU is instead implemented in terms > of SRCU-fast, which instead increments per-CPU counters. Which among > other thins is a bit faster and does not need to hook into the scheduler. Isn't that rather architecture dependant? It is fine on x86, but on arm incrementing a per-cpu variable is significantly expensive. David