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 2DDEAC10F13 for ; Tue, 16 Apr 2019 10:05:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 084FC206B6 for ; Tue, 16 Apr 2019 10:05:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728902AbfDPKFz (ORCPT ); Tue, 16 Apr 2019 06:05:55 -0400 Received: from terminus.zytor.com ([198.137.202.136]:47505 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726070AbfDPKFz (ORCPT ); Tue, 16 Apr 2019 06:05:55 -0400 Received: from terminus.zytor.com (localhost [127.0.0.1]) by terminus.zytor.com (8.15.2/8.15.2) with ESMTPS id x3GA3Hhx3398833 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Tue, 16 Apr 2019 03:03:17 -0700 Received: (from tipbot@localhost) by terminus.zytor.com (8.15.2/8.15.2/Submit) id x3GA3HhC3398830; Tue, 16 Apr 2019 03:03:17 -0700 Date: Tue, 16 Apr 2019 03:03:17 -0700 X-Authentication-Warning: terminus.zytor.com: tipbot set sender to tipbot@zytor.com using -f From: tip-bot for Waiman Long Message-ID: Cc: paulmck@linux.vnet.ibm.com, hpa@zytor.com, a.p.zijlstra@chello.nl, bp@alien8.de, dave@stgolabs.net, mingo@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, longman@redhat.com, peterz@infradead.org, dbueso@suse.de, tglx@linutronix.de, will.deacon@arm.com, linux-kernel@vger.kernel.org, tim.c.chen@linux.intel.com, arnd@arndb.de Reply-To: will.deacon@arm.com, linux-kernel@vger.kernel.org, tim.c.chen@linux.intel.com, arnd@arndb.de, longman@redhat.com, peterz@infradead.org, tglx@linutronix.de, dbueso@suse.de, torvalds@linux-foundation.org, mingo@kernel.org, akpm@linux-foundation.org, paulmck@linux.vnet.ibm.com, hpa@zytor.com, dave@stgolabs.net, bp@alien8.de, a.p.zijlstra@chello.nl In-Reply-To: <20190404174320.22416-5-longman@redhat.com> References: <20190404174320.22416-5-longman@redhat.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:locking/core] locking/rwsem: Micro-optimize rwsem_try_read_lock_unqueued() Git-Commit-ID: a338ecb07a338c9a8b0ca0010e862ebe598b1551 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: a338ecb07a338c9a8b0ca0010e862ebe598b1551 Gitweb: https://git.kernel.org/tip/a338ecb07a338c9a8b0ca0010e862ebe598b1551 Author: Waiman Long AuthorDate: Thu, 4 Apr 2019 13:43:13 -0400 Committer: Ingo Molnar CommitDate: Wed, 10 Apr 2019 10:56:01 +0200 locking/rwsem: Micro-optimize rwsem_try_read_lock_unqueued() The atomic_long_cmpxchg_acquire() in rwsem_try_read_lock_unqueued() is replaced by atomic_long_try_cmpxchg_acquire() to simpify the code and generate slightly better assembly code. There is no functional change. Signed-off-by: Waiman Long Acked-by: Peter Zijlstra Acked-by: Will Deacon Acked-by: Davidlohr Bueso Cc: Andrew Morton Cc: Arnd Bergmann Cc: Borislav Petkov Cc: Davidlohr Bueso Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Tim Chen Link: http://lkml.kernel.org/r/20190404174320.22416-5-longman@redhat.com Signed-off-by: Ingo Molnar --- kernel/locking/rwsem-xadd.c | 15 +++++---------- 1 file changed, 5 insertions(+), 10 deletions(-) diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index c213869e1aa7..f6198e1a58f6 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -259,21 +259,16 @@ static inline bool rwsem_try_write_lock(long count, struct rw_semaphore *sem) */ static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem) { - long old, count = atomic_long_read(&sem->count); + long count = atomic_long_read(&sem->count); - while (true) { - if (!(count == 0 || count == RWSEM_WAITING_BIAS)) - return false; - - old = atomic_long_cmpxchg_acquire(&sem->count, count, - count + RWSEM_ACTIVE_WRITE_BIAS); - if (old == count) { + while (!count || count == RWSEM_WAITING_BIAS) { + if (atomic_long_try_cmpxchg_acquire(&sem->count, &count, + count + RWSEM_ACTIVE_WRITE_BIAS)) { rwsem_set_owner(sem); return true; } - - count = old; } + return false; } static inline bool owner_on_cpu(struct task_struct *owner)