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=-8.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,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 8F022C4360C for ; Tue, 8 Oct 2019 16:30:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6492D206C2 for ; Tue, 8 Oct 2019 16:30:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="qVn3MqVk" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727753AbfJHQab (ORCPT ); Tue, 8 Oct 2019 12:30:31 -0400 Received: from mail-pg1-f195.google.com ([209.85.215.195]:41473 "EHLO mail-pg1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727865AbfJHQab (ORCPT ); Tue, 8 Oct 2019 12:30:31 -0400 Received: by mail-pg1-f195.google.com with SMTP id t3so4691922pga.8 for ; Tue, 08 Oct 2019 09:30:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=Jb1e68IiBAcctWybGAcBifRERsBYBG2XWgpUo+6+j8s=; b=qVn3MqVktxq2PUYzf97Mb1SsnXuU+CFrRmTeW9eaoQCcqc50A6TjepVChlhQLfxJZI eYrx9Up4Gdlbf5bIb8lWUhiLDhQAqDJWA7l6T0Xv4Icv/pU8iWZwMdT+a/XvwA0n+jnF 56H1E9/RMO6FNRHq4K14CXMhUJ90a+rGI1IiM= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=Jb1e68IiBAcctWybGAcBifRERsBYBG2XWgpUo+6+j8s=; b=IzmaFsCZ0r5n76NklSX7Bh98aqBw3wwbxkzTEIUaf6cq1ymSipf3nMF6gMLkOkhfMN hCD8yc7H8AIWTsj7H4K6HulPrAH4rK8pDz1NEXJMFdTn9YHLZT34zY3GVp6j8a/6jjkb LpzpdBOM4LZHZfGGaslxs/TEhUbxoRoxGYArOu1nQu13opWQB10noE+sxRpaYA3rBvv8 qmkasFaOrH37kMCiU7tOci7DzPtiohuOB8u1NZ+7HHf9KFbcsvMSJ2EHCt3NhhvOX+QM FI6wkZXhsHLWW/JCg8aiJOk7j8W4nwTo8jQZsm0Dt7WGzmZSgcGjUAOmwm7lbFJCggjV o5Tg== X-Gm-Message-State: APjAAAXM1aO/yFRrQiuHLEgYsBZ3OM77FH4tThclDQkqNqAIx89557gD UhOgA7Nm7ip/wJzI2wKdXSdbtOWTDEE= X-Google-Smtp-Source: APXvYqwjuiy6CnH1/xDdp+rt+p65xPZO6oE3SNppoNWoz7D5UyGsdWqbYJXadjf/wHbWyR+ZjUvoLw== X-Received: by 2002:a63:60e:: with SMTP id 14mr10751012pgg.179.1570552230117; Tue, 08 Oct 2019 09:30:30 -0700 (PDT) Received: from localhost ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id l192sm25589080pga.92.2019.10.08.09.30.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Oct 2019 09:30:29 -0700 (PDT) Date: Tue, 8 Oct 2019 12:30:28 -0400 From: Joel Fernandes To: Boqun Feng Cc: linux-kernel@vger.kernel.org, elver@google.com, "Paul E. McKenney" , Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , rcu@vger.kernel.org Subject: Re: [PATCH] rcu: Avoid to modify mask_ofl_ipi in sync_rcu_exp_select_node_cpus() Message-ID: <20191008163028.GA136151@google.com> 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/1.10.1 (2018-07-13) Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@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 > --- Reviewed-by: Joel Fernandes (Google) thanks, - Joel > 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 >