From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C1830C55178 for ; Thu, 5 Nov 2020 23:09:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6DD8B221FE for ; Thu, 5 Nov 2020 23:09:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604617770; bh=7xS20ktOREQzxIaFwCvXOEYKfqsP1oqb+blfshECMDo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=CRGw1QeTU1mzyAVg9THV3III4X7xkZBZb4WvUYnpuGMOI+6zpuJUQtqWhEw8rBSXo zAPlOeq15PGQrafYnCm3K3HyvwQAuMaRWXpmxulPILaKM0a+qz2tPV0g/0agLJ16k+ wjqYSRD8JJvI4zzESaKaG5ncd4oPQFNEvyfeXRLs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732162AbgKEXJ3 (ORCPT ); Thu, 5 Nov 2020 18:09:29 -0500 Received: from mail.kernel.org ([198.145.29.99]:34538 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732587AbgKEXJ1 (ORCPT ); Thu, 5 Nov 2020 18:09:27 -0500 Received: from paulmck-ThinkPad-P72.home (50-39-104-11.bvtn.or.frontiernet.net [50.39.104.11]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6149C2151B; Thu, 5 Nov 2020 23:09:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604617766; bh=7xS20ktOREQzxIaFwCvXOEYKfqsP1oqb+blfshECMDo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=vFMkNl7FVHe+EQCboSilPckMX+vyolRfMyvYojOzJgYNp774IjUd4f8sJOlT22v5f uMeI4l/7XGXhoDo/ry3zMBeAkK8pKo3rhTYkhLf5KSoYAMkFGoQdoGToba+0cYUEQM jLhwbazDdz8j9fO5SkTp1EK+vr3AJrYvdWmztJnA= From: paulmck@kernel.org To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, Neeraj Upadhyay , "Paul E . McKenney" Subject: [PATCH tip/core/rcu 07/16] rcu: Clarify nocb kthreads naming in RCU_NOCB_CPU config Date: Thu, 5 Nov 2020 15:09:12 -0800 Message-Id: <20201105230921.19017-7-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20201105230856.GA18904@paulmck-ThinkPad-P72> References: <20201105230856.GA18904@paulmck-ThinkPad-P72> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Neeraj Upadhyay This commit clarifies that the "p" and the "s" in the in the RCU_NOCB_CPU config-option description refer to the "x" in the "rcuox/N" kthread name. Signed-off-by: Neeraj Upadhyay [ paulmck: While in the area, update description and advice. ] Signed-off-by: Paul E. McKenney --- kernel/rcu/Kconfig | 20 ++++++++++++-------- 1 file changed, 12 insertions(+), 8 deletions(-) diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig index b71e21f..cdc57b4 100644 --- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -221,19 +221,23 @@ config RCU_NOCB_CPU Use this option to reduce OS jitter for aggressive HPC or real-time workloads. It can also be used to offload RCU callback invocation to energy-efficient CPUs in battery-powered - asymmetric multiprocessors. + asymmetric multiprocessors. The price of this reduced jitter + is that the overhead of call_rcu() increases and that some + workloads will incur significant increases in context-switch + rates. This option offloads callback invocation from the set of CPUs specified at boot time by the rcu_nocbs parameter. For each such CPU, a kthread ("rcuox/N") will be created to invoke callbacks, where the "N" is the CPU being offloaded, and where - the "p" for RCU-preempt (PREEMPTION kernels) and "s" for RCU-sched - (!PREEMPTION kernels). Nothing prevents this kthread from running - on the specified CPUs, but (1) the kthreads may be preempted - between each callback, and (2) affinity or cgroups can be used - to force the kthreads to run on whatever set of CPUs is desired. - - Say Y here if you want to help to debug reduced OS jitter. + the "x" is "p" for RCU-preempt (PREEMPTION kernels) and "s" for + RCU-sched (!PREEMPTION kernels). Nothing prevents this kthread + from running on the specified CPUs, but (1) the kthreads may be + preempted between each callback, and (2) affinity or cgroups can + be used to force the kthreads to run on whatever set of CPUs is + desired. + + Say Y here if you need reduced OS jitter, despite added overhead. Say N here if you are unsure. config TASKS_TRACE_RCU_READ_MB -- 2.9.5