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=-12.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,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 28865C433E0 for ; Fri, 22 Jan 2021 15:38:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E9BCF20702 for ; Fri, 22 Jan 2021 15:38:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729033AbhAVPhn (ORCPT ); Fri, 22 Jan 2021 10:37:43 -0500 Received: from mail.kernel.org ([198.145.29.99]:53054 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728894AbhAVPgW (ORCPT ); Fri, 22 Jan 2021 10:36:22 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 508E6206A4; Fri, 22 Jan 2021 15:35:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1611329741; bh=WG6IzHZ750YD/dhJrEgxww5BN2aFxSjz9Zbw7htUOyI=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=Of07N0rmMyfV08auVII1TMwOfHK75L2r454+L2BIYa8eS2IXbouPIV9wR56sJ58Ce jAJ/2pPLp/07yC9fexIxb0ljRTurMjR4t0pc5eJId8LiM07pu+xCdZTcvTYNp/knOE BCYRGeCXWN/6SpcklFXd+eEibx/wikQ1tDCVFZJX9xb3QIPyLQY/+u9L7ch48SESrm ALC+sGvCzfayufJ6xB+iLPkx69bwjNh/YEBDurtMtcdlcfizNTtG7X075hkA8XpnG2 mTRcQYxzjHwBuaTpMpYECOSLnhju1/Vn/wkYJoP8k8PZ6cDSy54mLwZSzzg4in0n2i HuM6f+iSJofJA== Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 05D053522649; Fri, 22 Jan 2021 07:35:41 -0800 (PST) Date: Fri, 22 Jan 2021 07:35:41 -0800 From: "Paul E. McKenney" To: Peter Zijlstra Cc: tglx@linutronix.de, frederic@kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, cai@lca.pw, mgorman@techsingularity.net, joel@joelfernandes.org, valentin.schneider@arm.com Subject: Re: [RFC][PATCH 4/7] smp: Optimize send_call_function_single_ipi() Message-ID: <20210122153540.GF2743@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200526161057.531933155@infradead.org> <20200526161907.953304789@infradead.org> <20200527095645.GH325280@hirez.programming.kicks-ass.net> <20200527101513.GJ325303@hirez.programming.kicks-ass.net> <20200527155656.GU2869@paulmck-ThinkPad-P72> <20200527163543.GA706478@hirez.programming.kicks-ass.net> <20200527171236.GC706495@hirez.programming.kicks-ass.net> <20210122002012.GB2743@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 22, 2021 at 09:31:37AM +0100, Peter Zijlstra wrote: > On Thu, Jan 21, 2021 at 04:20:12PM -0800, Paul E. McKenney wrote: > > > > --- > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > > index 368749008ae8..2c8d4c3e341e 100644 > > > --- a/kernel/rcu/tree.c > > > +++ b/kernel/rcu/tree.c > > > @@ -445,7 +445,7 @@ static int rcu_is_cpu_rrupt_from_idle(void) > > > /* > > > * Usually called from the tick; but also used from smp_function_call() > > > * for expedited grace periods. This latter can result in running from > > > - * the idle task, instead of an actual IPI. > > > + * a (usually the idle) task, instead of an actual IPI. > > > > The story is growing enough hair that we should tell it only once. > > So here just where it is called from: > > > > /* > > * Usually called from the tick; but also used from smp_function_call() > > * for expedited grace periods. > > */ > > > > > lockdep_assert_irqs_disabled(); > > > > > > @@ -461,9 +461,14 @@ static int rcu_is_cpu_rrupt_from_idle(void) > > > return false; > > > > > > /* > > > - * If we're not in an interrupt, we must be in the idle task! > > > + * If we're not in an interrupt, we must be in task context. > > > + * > > > + * This will typically be the idle task through: > > > + * flush_smp_call_function_from_idle(), > > > + * > > > + * but can also be in CPU HotPlug through smpcfd_dying(). > > > */ > > > > Good, but how about like this? > > > > /* > > * If we are not in an interrupt handler, we must be in > > * smp_call_function() handler. > > * > > * Normally, smp_call_function() handlers are invoked from > > * the idle task via flush_smp_call_function_from_idle(). > > * However, they can also be invoked from CPU hotplug > > * operations via smpcfd_dying(). > > */ > > > > > - WARN_ON_ONCE(!nesting && !is_idle_task(current)); > > > + WARN_ON_ONCE(!nesting && !in_task(current)); > > > > This is used in time-critical contexts, so why not RCU_LOCKDEP_WARN()? > > That should also allow checking more closely. Would something like the > > following work? > > > > RCU_LOCKDEP_WARN(!nesting && !is_idle_task(current) && (!in_task(current) || !lockdep_cpus_write_held())); > > > > Where lockdep_cpus_write_held is defined in kernel/cpu.c: > > Works for me, except s/in_task(current)/in_task()/ compiles a lot > better. These compilers sure constrain my creativity! ;-) Might be a good thing, though... Thanx, Paul