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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 56978C4332B for ; Thu, 19 Mar 2020 23:58:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1EE6120753 for ; Thu, 19 Mar 2020 23:58:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584662311; bh=1Iilp28i0bCTskgCsO8oASv9W7OdeQt1V3gTWMx3C9w=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=U2jHJ4FdWTb6e9V0CwSE3Bh7d8esefwwS51ClsLq0tMcw4zcY1Ic9ojaWWey0Rtu1 s4RCjGm8Ion2Qh3R4/ZaPP8c5kWGAv2rKUOrWUer8i1grsbYzaG6UYo1Oi6CCGek9+ i27aR5ZWF0LwAtgR00UvubbEc/6/PA/M6jn/gOLY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727244AbgCSX6a (ORCPT ); Thu, 19 Mar 2020 19:58:30 -0400 Received: from mail.kernel.org ([198.145.29.99]:48502 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727159AbgCSX6a (ORCPT ); Thu, 19 Mar 2020 19:58:30 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (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 7C21C20754; Thu, 19 Mar 2020 23:58:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584662309; bh=1Iilp28i0bCTskgCsO8oASv9W7OdeQt1V3gTWMx3C9w=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=elmVnY1ABSGb+xRrvQ9PcXrqvEzg7FUzJ8x5d4XySe6/R7CY5EuUbuwIqVmiHvmYk Oeroik0vKThlwP2ABGqsFEnevbm2UG7svAs2L0l7b4i4BbWUfVJHHE05dawmBDhHpv h8Pn9EhppW+Ju+LisnA8r3T6cMvB0Hych4BTQ+lg= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 49DA235226B9; Thu, 19 Mar 2020 16:58:29 -0700 (PDT) Date: Thu, 19 Mar 2020 16:58:29 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org Subject: Re: [PATCH RFC v2 tip/core/rcu 09/22] rcu-tasks: Add an RCU-tasks rude variant Message-ID: <20200319235829.GK3199@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200319001024.GA28798@paulmck-ThinkPad-P72> <20200319001100.24917-9-paulmck@kernel.org> <20200319150432.1ac9dac9@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200319150432.1ac9dac9@gandalf.local.home> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Thu, Mar 19, 2020 at 03:04:32PM -0400, Steven Rostedt wrote: > On Wed, 18 Mar 2020 17:10:47 -0700 > paulmck@kernel.org wrote: > > > From: "Paul E. McKenney" > > > > This commit adds a "rude" variant of RCU-tasks that has as quiescent > > states schedule(), cond_resched_tasks_rcu_qs(), userspace execution, > > and (in theory, anyway) cond_resched(). In other words, RCU-tasks rude > > readers are regions of code with preemption disabled, but excluding code > > early in the CPU-online sequence and late in the CPU-offline sequence. > > Updates make use of IPIs and force an IPI and a context switch on each > > online CPU. This variant is useful in some situations in tracing. > > > > Suggested-by: Steven Rostedt > > [ paulmck: Apply EXPORT_SYMBOL_GPL() feedback from Qiujun Huang. ] > > Signed-off-by: Paul E. McKenney > > --- > > include/linux/rcupdate.h | 3 ++ > > kernel/rcu/Kconfig | 12 +++++- > > kernel/rcu/tasks.h | 98 ++++++++++++++++++++++++++++++++++++++++++++++++ > > 3 files changed, 112 insertions(+), 1 deletion(-) > > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > index 5523145..2be97a8 100644 > > --- a/include/linux/rcupdate.h > > +++ b/include/linux/rcupdate.h > > @@ -37,6 +37,7 @@ > > /* Exported common interfaces */ > > void call_rcu(struct rcu_head *head, rcu_callback_t func); > > void rcu_barrier_tasks(void); > > +void rcu_barrier_tasks_rude(void); > > void synchronize_rcu(void); > > > > #ifdef CONFIG_PREEMPT_RCU > > @@ -138,6 +139,8 @@ static inline void rcu_init_nohz(void) { } > > #define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t) > > void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); > > void synchronize_rcu_tasks(void); > > +void call_rcu_tasks_rude(struct rcu_head *head, rcu_callback_t func); > > +void synchronize_rcu_tasks_rude(void); > > void exit_tasks_rcu_start(void); > > void exit_tasks_rcu_finish(void); > > #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ > > diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig > > index 38475d0..0d43ec1 100644 > > --- a/kernel/rcu/Kconfig > > +++ b/kernel/rcu/Kconfig > > @@ -71,7 +71,7 @@ config TREE_SRCU > > This option selects the full-fledged version of SRCU. > > > > config TASKS_RCU_GENERIC > > - def_bool TASKS_RCU > > + def_bool TASKS_RCU || TASKS_RUDE_RCU > > select SRCU > > help > > This option enables generic infrastructure code supporting > > @@ -84,6 +84,16 @@ config TASKS_RCU > > only voluntary context switch (not preemption!), idle, and > > user-mode execution as quiescent states. Not for manual selection. > > > > +config TASKS_RUDE_RCU > > + def_bool 0 > > + default n > > No need for "default n" as that's the default without it. Removed! > > + help > > + This option enables a task-based RCU implementation that uses > > + only context switch (including preemption) and user-mode > > + execution as quiescent states. It forces IPIs and context > > + switches on all online CPUs, including idle ones, so use > > + with caution. Not for manual selection. > > Really don't need the "Not for manual selection", as not having a prompt > shows that too. And also removed. > > + > > config RCU_STALL_COMMON > > def_bool TREE_RCU > > help > > diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h > > index d77921e..7ba1730 100644 > > --- a/kernel/rcu/tasks.h > > +++ b/kernel/rcu/tasks.h > > @@ -180,6 +180,9 @@ static void __init rcu_tasks_bootup_oddness(void) > > else > > pr_info("\tTasks RCU enabled.\n"); > > #endif /* #ifdef CONFIG_TASKS_RCU */ > > +#ifdef CONFIG_TASKS_RUDE_RCU > > + pr_info("\tRude variant of Tasks RCU enabled.\n"); > > +#endif /* #ifdef CONFIG_TASKS_RUDE_RCU */ > > } > > > > #endif /* #ifndef CONFIG_TINY_RCU */ > > @@ -410,3 +413,98 @@ static int __init rcu_spawn_tasks_kthread(void) > > core_initcall(rcu_spawn_tasks_kthread); > > > > #endif /* #ifdef CONFIG_TASKS_RCU */ > > + > > +#ifdef CONFIG_TASKS_RUDE_RCU > > + > > +//////////////////////////////////////////////////////////////////////// > > +// > > +// "Rude" variant of Tasks RCU, inspired by Steve Rostedt's trick of > > +// passing an empty function to schedule_on_each_cpu(). This approach > > +// provides an asynchronous call_rcu_rude() API and batching of concurrent > > +// calls to the synchronous synchronize_rcu_rude() API. This sends IPIs > > +// far and wide and induces otherwise unnecessary context switches on all > > +// online CPUs, whether online or not. > > "on all online CPUs, whether online or not" ???? Good catch! It should be "whether idle or not". Fixed. ;-) Thanx, Paul > -- Steve > > > + > > +// Empty function to allow workqueues to force a context switch. > > +static void rcu_tasks_be_rude(struct work_struct *work) > > +{ > > +} > > +