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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DEEE6C433F5 for ; Mon, 18 Apr 2022 23:57:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235988AbiDSAAh (ORCPT ); Mon, 18 Apr 2022 20:00:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41830 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235925AbiDSAAe (ORCPT ); Mon, 18 Apr 2022 20:00:34 -0400 Received: from mail-pg1-x52c.google.com (mail-pg1-x52c.google.com [IPv6:2607:f8b0:4864:20::52c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8BE4629CA7 for ; Mon, 18 Apr 2022 16:57:54 -0700 (PDT) Received: by mail-pg1-x52c.google.com with SMTP id t13so21732149pgn.8 for ; Mon, 18 Apr 2022 16:57:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=6DTfyGY4J+aCud1WtrxDpmeZLZK9HwCoRH/ZKq7p0NY=; b=MpJYZqhS/4wevygKpX5CVGmCIl7fpr/siGQ+44MFb9SHbahqi50UNuu5Rol1xchxjN aNky1Oy1UkUOLUOAKwBTb4JXgAuRru33uEuY9kTeCdLaZUZb+MnwrkYEU8FnELc4oqPm kAB/WHOilbj00EbxBKW+LNOdSwg57Zh+qtJ3480IneLi31Upq7YzBEx6d94gCDrUZYKM KuV0Sw/+ZPbympbXikCSy0hv5RuOsnx68DVBFKiPSTurvh/MZ7m5xiOw3GO1QpG7I+7T vbP4VmXtR027F0y7rPZnFWIR+5ixC0BQktvD6wNpz+rFr+oe2hV2Rxr7LEH2iuZLdkva d5EQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=6DTfyGY4J+aCud1WtrxDpmeZLZK9HwCoRH/ZKq7p0NY=; b=6ptKvEtA4EVuRK1zrEJCSIjEHMV/mXD2kcq5zTdbs1Uhfrh+L+jm12g0tmiinl4FvR BeF0Sg2sCejDjTEAFTzV8UF23oHEsAA8Ads0LikrBQ+Y09B0iHNEy2Vs1NLKexzVMbgq G7+fQEYXATliOibt7H6c6TZqTRbH1zNq9Q18/h1EVFb6dmXyX87TtSQqheL7xJ5ZgZ2D +7K2Q0U7gBy6SZvOb2RA3HtWEAz0yeqpL+mInNFw5QLckj6ruylB/GYte1NTtjiZbVso Gkl9IIDbeY8qRa598EY77hVmbcDvzoJEeQzGve0Ok/gopAxrapTvLamybmvLTqTA31FK 9pvA== X-Gm-Message-State: AOAM531LEZh4hT16sdvKVRn6F1d8uI7N/JOy+gKIVEl9659pO5cN/R3K Q2ZdOb5gKzdlSPdehwvs4dB6pA== X-Google-Smtp-Source: ABdhPJwGbAEcmZ3Ri9bRNtcMxJHs0CrJhc9Y8lGnJ3QNwvBq4WwRrkz1+U7Kith1lRipZxV8xB3qEw== X-Received: by 2002:a63:6e04:0:b0:398:409:2928 with SMTP id j4-20020a636e04000000b0039804092928mr12229537pgc.250.1650326273031; Mon, 18 Apr 2022 16:57:53 -0700 (PDT) Received: from google.com ([2620:15c:211:200:e2b4:e46f:41ee:4499]) by smtp.gmail.com with ESMTPSA id bc11-20020a656d8b000000b0039cc4dbb295sm13381698pgb.60.2022.04.18.16.57.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 18 Apr 2022 16:57:52 -0700 (PDT) Date: Mon, 18 Apr 2022 16:57:46 -0700 From: Kalesh Singh To: "Joel Fernandes (Google)" Cc: linux-kernel@vger.kernel.org, Josh Triplett , Lai Jiangshan , Mathieu Desnoyers , "Paul E. McKenney" , rcu@vger.kernel.org, Steven Rostedt , rushikesh.s.kadam@intel.com, vineethrp@gmail.com, urezki@gmail.com Subject: Re: [PATCH v4] rcu/nocb: Add an option to offload all CPUs on boot Message-ID: References: <20220418175403.2553842-1-joel@joelfernandes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220418175403.2553842-1-joel@joelfernandes.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 18, 2022 at 05:54:03PM +0000, Joel Fernandes (Google) wrote: > From: Joel Fernandes > > On systems with CONFIG_RCU_NOCB_CPU=y, there is no default mask provided > which ends up not offloading any CPU. This patch removes a dependency > from the bootloader having to know about RCU and about how to provide > the mask. > > With the new option enabled, all CPUs will be offloaded on boot unless > rcu_nocbs= or rcu_nohz_full= kernel parameters provide a CPU list. > > Signed-off-by: Joel Fernandes Hi Joel, You can add Reviewed-by: Kalesh Singh Thanks, Kalesh > --- > v4: mostly style related fixes. > v3 is back to v1 but with a config option defaulting to 'n'. > v2 was forcing the option to override no_cbs= > > Documentation/admin-guide/kernel-parameters.txt | 6 ++++++ > kernel/rcu/Kconfig | 13 +++++++++++++ > kernel/rcu/tree_nocb.h | 15 ++++++++++++++- > 3 files changed, 33 insertions(+), 1 deletion(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index f5a27f067db9..4beb15ccac1a 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -3506,6 +3506,9 @@ > just as if they had also been called out in the > rcu_nocbs= boot parameter. > > + Note that this argument takes precedence over > + the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. > + > noiotrap [SH] Disables trapped I/O port accesses. > > noirqdebug [X86-32] Disables the code which attempts to detect and > @@ -4398,6 +4401,9 @@ > no-callback mode from boot but the mode may be > toggled at runtime via cpusets. > > + Note that this argument takes precedence over > + the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. > + > rcu_nocb_poll [KNL] > Rather than requiring that offloaded CPUs > (specified by rcu_nocbs= above) explicitly > diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig > index bf8e341e75b4..746a668bf81d 100644 > --- a/kernel/rcu/Kconfig > +++ b/kernel/rcu/Kconfig > @@ -223,6 +223,19 @@ config RCU_NOCB_CPU > Say Y here if you need reduced OS jitter, despite added overhead. > Say N here if you are unsure. > > +config RCU_NOCB_CPU_DEFAULT_ALL > + bool "Offload RCU callback processing from all CPUs by default" > + depends on RCU_NOCB_CPU > + default n > + help > + Use this option to offload callback processing from all CPUs > + by default, in the absence of the rcu_nocbs or nohz_full boot > + parameter. This also avoids the need to use any boot parameters > + to achieve the effect of offloading all CPUs on boot. > + > + Say Y here if you want offload all CPUs by default on boot. > + Say N here if you are unsure. > + > config TASKS_TRACE_RCU_READ_MB > bool "Tasks Trace RCU readers use memory barriers in user and idle" > depends on RCU_EXPERT > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h > index eeafb546a7a0..f648f773600a 100644 > --- a/kernel/rcu/tree_nocb.h > +++ b/kernel/rcu/tree_nocb.h > @@ -1166,11 +1166,21 @@ void __init rcu_init_nohz(void) > { > int cpu; > bool need_rcu_nocb_mask = false; > + bool offload_all = false; > struct rcu_data *rdp; > > +#if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) > + if (!rcu_nocb_is_setup) { > + need_rcu_nocb_mask = true; > + offload_all = true; > + } > +#endif > + > #if defined(CONFIG_NO_HZ_FULL) > - if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask)) > + if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask)) { > need_rcu_nocb_mask = true; > + offload_all = false; /* NO_HZ_FULL has its own mask. */ > + } > #endif /* #if defined(CONFIG_NO_HZ_FULL) */ > > if (need_rcu_nocb_mask) { > @@ -1191,6 +1201,9 @@ void __init rcu_init_nohz(void) > cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask); > #endif /* #if defined(CONFIG_NO_HZ_FULL) */ > > + if (offload_all) > + cpumask_setall(rcu_nocb_mask); > + > if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { > pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n"); > cpumask_and(rcu_nocb_mask, cpu_possible_mask, > -- > 2.36.0.rc0.470.gd361397f0d-goog > >