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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 0505EC43143 for ; Fri, 22 Jun 2018 06:24:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 41E0A23D5A for ; Fri, 22 Jun 2018 06:24:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 41E0A23D5A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lge.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751182AbeFVGX6 (ORCPT ); Fri, 22 Jun 2018 02:23:58 -0400 Received: from lgeamrelo11.lge.com ([156.147.23.51]:53478 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750913AbeFVGX5 (ORCPT ); Fri, 22 Jun 2018 02:23:57 -0400 Received: from unknown (HELO lgeamrelo01.lge.com) (156.147.1.125) by 156.147.23.51 with ESMTP; 22 Jun 2018 15:23:54 +0900 X-Original-SENDERIP: 156.147.1.125 X-Original-MAILFROM: byungchul.park@lge.com Received: from unknown (HELO X58A-UD3R) (10.177.222.33) by 156.147.1.125 with ESMTP; 22 Jun 2018 15:23:54 +0900 X-Original-SENDERIP: 10.177.222.33 X-Original-MAILFROM: byungchul.park@lge.com Date: Fri, 22 Jun 2018 15:23:51 +0900 From: Byungchul Park To: jiangshanlai@gmail.com, paulmck@linux.vnet.ibm.com, josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com Cc: linux-kernel@vger.kernel.org, kernel-team@lge.com, joel@joelfernandes.org Subject: Re: [PATCH] rcu: Refactor rcu_{nmi,irq}_{enter,exit}() Message-ID: <20180622062351.GC17010@X58A-UD3R> References: <1529647926-24427-1-git-send-email-byungchul.park@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1529647926-24427-1-git-send-email-byungchul.park@lge.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 22, 2018 at 03:12:06PM +0900, Byungchul Park wrote: > When passing through irq or NMI contexts, the current code uses > ->dynticks_nmi_nesting to detect if it's in the ourmost at the moment. > > Here, the thing is that all the related functions, rcu_irq_enter(), > rcu_nmi_enter(), rcu_irq_exit() and rcu_nmi_exit() are carrying out > the check within each under the following call relationship so there > must be redundant conditional branches: > > rcu_irq_enter() > /* A conditional branch with ->dynticks_nmi_nesting */ > rcu_nmi_enter() > /* A conditional branch with ->dynticks_nmi_nesting */ ^ Precisely, ->dynticks > /* A conditional branch with ->dynticks_nmi_nesting */ > > rcu_irq_exit() > /* A conditional branch with ->dynticks_nmi_nesting */ > rcu_nmi_exit() > /* A conditional branch with ->dynticks_nmi_nesting */ > /* A conditional branch with ->dynticks_nmi_nesting */ > > rcu_nmi_enter() > /* A conditional branch with ->dynticks_nmi_nesting */ ^ Precisely, ->dynticks > > rcu_nmi_exit() > /* A conditional branch with ->dynticks_nmi_nesting */ > > In order to make the code more readable and remove redundant > conditional branches, we need to refactor rcu_{nmi,irq}_{enter,exit}() > so they use a common function for each like: > > rcu_irq_enter() inlining rcu_nmi_enter_common(irq) > /* A conditional branch with ->dynticks_nmi_nesting */ ^ Precisely, ->dynticks > > rcu_irq_exit() inlining rcu_nmi_exit_common(irq) > /* A conditional branch with ->dynticks_nmi_nesting */ > > rcu_nmi_enter() inlining rcu_nmi_enter_common(nmi) > /* A conditional branch with ->dynticks_nmi_nesting */ ^ Precisely, ->dynticks > > rcu_nmi_exit() inlining rcu_nmi_exit_common(nmi) > /* A conditional branch with ->dynticks_nmi_nesting */