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=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 65E41C4360C for ; Tue, 8 Oct 2019 13:13:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3A5A620815 for ; Tue, 8 Oct 2019 13:13:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570540381; bh=6C1HT7Hwuk66VyyK5prFO+ijNSykLia8L0KvWsOuPnQ=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=KJarlUuvshyW6sC+QGbPNP9ql+fmbNj089xu1Be2+kyw1h/F2NlFJqfOAIOkiF6+c 5D4oLfl5LHOUS0RHVwQgkgd0DWfvCVVObD/feJOyizEjV5O3PgystAWzQmmTwtmg7e dtMj9GwMAQackG+UkBXXoYKaiNeqgDZPCdPTLFJg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731015AbfJHNNA (ORCPT ); Tue, 8 Oct 2019 09:13:00 -0400 Received: from mail.kernel.org ([198.145.29.99]:51340 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730317AbfJHNNA (ORCPT ); Tue, 8 Oct 2019 09:13:00 -0400 Received: from paulmck-ThinkPad-P72 (unknown [12.12.162.101]) (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 5D3C42070B; Tue, 8 Oct 2019 13:12:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570540379; bh=6C1HT7Hwuk66VyyK5prFO+ijNSykLia8L0KvWsOuPnQ=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=WaJCh8iLf0y38iGS1Bc0RD4wGkA3zVBPwAK95dw1l9/1dJExMQFOjl+5FkRdYBOn6 DiTPS8Q8vTg4aggaRMlZDx0O6DbH4X8+xOYeOgXYksFIgxoFyIIKg2O2QiCdEvRgDt e4fymIVKS3db8QWsMAQ4LXcDnq8EyPGmer1uLcJ8= Date: Tue, 8 Oct 2019 06:12:58 -0700 From: "Paul E. McKenney" To: Boqun Feng Cc: linux-kernel@vger.kernel.org, elver@google.com, Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , rcu@vger.kernel.org Subject: Re: [PATCH] rcu: Avoid to modify mask_ofl_ipi in sync_rcu_exp_select_node_cpus() Message-ID: <20191008131258.GU2689@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20191008050145.4041702-1-boqun.feng@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191008050145.4041702-1-boqun.feng@gmail.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 08, 2019 at 01:01:40PM +0800, Boqun Feng wrote: > "mask_ofl_ipi" is used for iterate CPUs which IPIs are needed to send > to, however in the IPI sending loop, "mask_ofl_ipi" along with another > variable "mask_ofl_test" might also get modified to record which CPU's > quiesent state can be reported by sync_rcu_exp_select_node_cpus(). Two > variables seems to be redundant for such a propose, so this patch clean > things a little by solely using "mask_ofl_test" for recording and > "mask_ofl_ipi" for iteration. This would improve the readibility of the > IPI sending loop in sync_rcu_exp_select_node_cpus(). > > Signed-off-by: Boqun Feng Queued for further review and testing, thank you!!! Thanx, Paul > --- > kernel/rcu/tree_exp.h | 13 ++++++------- > 1 file changed, 6 insertions(+), 7 deletions(-) > > diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h > index 69c5aa64fcfd..212470018752 100644 > --- a/kernel/rcu/tree_exp.h > +++ b/kernel/rcu/tree_exp.h > @@ -387,10 +387,10 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp) > } > ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0); > put_cpu(); > - if (!ret) { > - mask_ofl_ipi &= ~mask; > + /* The CPU responses the IPI, and will report QS itself */ > + if (!ret) > continue; > - } > + > /* Failed, raced with CPU hotplug operation. */ > raw_spin_lock_irqsave_rcu_node(rnp, flags); > if ((rnp->qsmaskinitnext & mask) && > @@ -401,13 +401,12 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp) > schedule_timeout_uninterruptible(1); > goto retry_ipi; > } > - /* CPU really is offline, so we can ignore it. */ > - if (!(rnp->expmask & mask)) > - mask_ofl_ipi &= ~mask; > + /* CPU really is offline, and we need its QS to pass GP. */ > + if (rnp->expmask & mask) > + mask_ofl_test |= mask; > raw_spin_unlock_irqrestore_rcu_node(rnp, flags); > } > /* Report quiescent states for those that went offline. */ > - mask_ofl_test |= mask_ofl_ipi; > if (mask_ofl_test) > rcu_report_exp_cpu_mult(rnp, mask_ofl_test, false); > } > -- > 2.23.0 >