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=-12.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 F3A6FC7112F for ; Mon, 21 Jan 2019 11:29:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CC30320663 for ; Mon, 21 Jan 2019 11:29:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728261AbfAUL3Y (ORCPT ); Mon, 21 Jan 2019 06:29:24 -0500 Received: from terminus.zytor.com ([198.137.202.136]:50953 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727665AbfAUL3V (ORCPT ); Mon, 21 Jan 2019 06:29:21 -0500 Received: from terminus.zytor.com (localhost [127.0.0.1]) by terminus.zytor.com (8.15.2/8.15.2) with ESMTPS id x0LBSrJB2496189 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Mon, 21 Jan 2019 03:28:53 -0800 Received: (from tipbot@localhost) by terminus.zytor.com (8.15.2/8.15.2/Submit) id x0LBSri52496186; Mon, 21 Jan 2019 03:28:53 -0800 Date: Mon, 21 Jan 2019 03:28:53 -0800 X-Authentication-Warning: terminus.zytor.com: tipbot set sender to tipbot@zytor.com using -f From: tip-bot for Davidlohr Bueso Message-ID: Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, longman@redhat.com, akpm@linux-foundation.org, dave@stgolabs.net, peterz@infradead.org, tglx@linutronix.de, will.deacon@arm.com, elohimes@gmail.com, dbueso@suse.de, hpa@zytor.com, paulmck@linux.vnet.ibm.com, torvalds@linux-foundation.org Reply-To: peterz@infradead.org, tglx@linutronix.de, akpm@linux-foundation.org, dave@stgolabs.net, mingo@kernel.org, linux-kernel@vger.kernel.org, longman@redhat.com, torvalds@linux-foundation.org, elohimes@gmail.com, will.deacon@arm.com, dbueso@suse.de, paulmck@linux.vnet.ibm.com, hpa@zytor.com In-Reply-To: <20181203053130.gwkw6kg72azt2npb@linux-r8p5> References: <20181203053130.gwkw6kg72azt2npb@linux-r8p5> To: linux-tip-commits@vger.kernel.org Subject: [tip:locking/core] sched/wake_q: Add branch prediction hint to wake_q_add() cmpxchg Git-Commit-ID: 87ff19cb2f1aa55a5d8b691e6690cc059a59d2ec X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 87ff19cb2f1aa55a5d8b691e6690cc059a59d2ec Gitweb: https://git.kernel.org/tip/87ff19cb2f1aa55a5d8b691e6690cc059a59d2ec Author: Davidlohr Bueso AuthorDate: Sun, 2 Dec 2018 21:31:30 -0800 Committer: Ingo Molnar CommitDate: Mon, 21 Jan 2019 11:18:50 +0100 sched/wake_q: Add branch prediction hint to wake_q_add() cmpxchg The cmpxchg() will fail when the task is already in the process of waking up, and as such is an extremely rare occurrence. Micro-optimize the call and put an unlikely() around it. To no surprise, when using CONFIG_PROFILE_ANNOTATED_BRANCHES under a number of workloads the incorrect rate was a mere 1-2%. Signed-off-by: Davidlohr Bueso Signed-off-by: Peter Zijlstra (Intel) Acked-by: Waiman Long Cc: Andrew Morton Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Will Deacon Cc: Yongji Xie Cc: andrea.parri@amarulasolutions.com Cc: lilin24@baidu.com Cc: liuqi16@baidu.com Cc: nixun@baidu.com Cc: xieyongji@baidu.com Cc: yuanlinsi01@baidu.com Cc: zhangyu31@baidu.com Link: https://lkml.kernel.org/r/20181203053130.gwkw6kg72azt2npb@linux-r8p5 Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index d8d76a65cfdd..b05eef7d7a1f 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -421,7 +421,7 @@ void wake_q_add(struct wake_q_head *head, struct task_struct *task) * state, even in the failed case, an explicit smp_mb() must be used. */ smp_mb__before_atomic(); - if (cmpxchg_relaxed(&node->next, NULL, WAKE_Q_TAIL)) + if (unlikely(cmpxchg_relaxed(&node->next, NULL, WAKE_Q_TAIL))) return; get_task_struct(task);