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=-12.8 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_SANE_1 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 3BE62C4346E for ; Thu, 24 Sep 2020 23:00:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EB6BC23600 for ; Thu, 24 Sep 2020 23:00:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600988401; bh=FnlDJ4w2Wp7B+ooR/U+JqMBTHrFYFwOTHlid0jHxpp0=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=pjbTVblTZJ8esg0nOxT8J0NVbGUjow9+b496GSkEZ6YLod05muc0jilPTqpttjJaG PtkEsayBSfWYMOydtxI638w80uKcI67EwgX6jw1nfCSXHF9b2PRqphjnJ2F0SF2Myj itUWRWYFVLdaMtL9paxu/eXfs2GMTpwa7BIvCA3k= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726700AbgIXXAA (ORCPT ); Thu, 24 Sep 2020 19:00:00 -0400 Received: from mail.kernel.org ([198.145.29.99]:33722 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726205AbgIXXAA (ORCPT ); Thu, 24 Sep 2020 19:00:00 -0400 Received: from paulmck-ThinkPad-P72.home (unknown [50.45.173.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E75782344C; Thu, 24 Sep 2020 22:59:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600988399; bh=FnlDJ4w2Wp7B+ooR/U+JqMBTHrFYFwOTHlid0jHxpp0=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=BoKgzIPcUFGxxWG1d0l4lyQ9LcVunTMUK+FQSYmr9qH3iwtZ7pKeS49P3OGiw4mWW tgStj13sQxhdQGeFuZPs/3TZ3RAR53f/77sWn7BTAoGmHAuQTUtPu3SGJjX/fazSmd 6yXWIW+X6fNRSRAhc0nmuaactMyCyyk7R8Iyfdpg= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id B2C9435230AC; Thu, 24 Sep 2020 15:59:59 -0700 (PDT) Date: Thu, 24 Sep 2020 15:59:59 -0700 From: "Paul E. McKenney" To: Neeraj Upadhyay Cc: josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, joel@joelfernandes.org, rcu@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] rcu: Clarify nocb kthreads naming in RCU_NOCB_CPU config Message-ID: <20200924225959.GY29330@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <1600929250-20344-1-git-send-email-neeraju@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1600929250-20344-1-git-send-email-neeraju@codeaurora.org> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Thu, Sep 24, 2020 at 12:04:10PM +0530, Neeraj Upadhyay wrote: > Clarify the "x" in rcuox/N naming in RCU_NOCB_CPU config > description. > > Signed-off-by: Neeraj Upadhyay Applied with a few additional updates as shown below. As always, please let me know if I messed anything up. Thanx, Paul ------------------------------------------------------------------------ commit 8d1d776b4998896a6f8f4608edb0b258bd37ec9f Author: Neeraj Upadhyay Date: Thu Sep 24 12:04:10 2020 +0530 rcu: Clarify nocb kthreads naming in RCU_NOCB_CPU config 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 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