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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY,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 11455C2D0B1 for ; Tue, 4 Feb 2020 10:18:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DDFCB20674 for ; Tue, 4 Feb 2020 10:18:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726741AbgBDKSK (ORCPT ); Tue, 4 Feb 2020 05:18:10 -0500 Received: from out30-56.freemail.mail.aliyun.com ([115.124.30.56]:41231 "EHLO out30-56.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726554AbgBDKSJ (ORCPT ); Tue, 4 Feb 2020 05:18:09 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R171e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04396;MF=alex.shi@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0Tp874Rw_1580811484; Received: from IT-FVFX43SYHV2H.local(mailfrom:alex.shi@linux.alibaba.com fp:SMTPD_---0Tp874Rw_1580811484) by smtp.aliyun-inc.com(127.0.0.1); Tue, 04 Feb 2020 18:18:05 +0800 Subject: Re: [PATCH] locking/rtmutex: remove unused cmpxchg_relaxed To: Thomas Gleixner , Davidlohr Bueso Cc: Peter Zijlstra , Ingo Molnar , Will Deacon , linux-kernel@vger.kernel.org References: <1579595686-251535-1-git-send-email-alex.shi@linux.alibaba.com> <20200131173922.hjvugxuybrn2wbsn@linux-p48b> <87r1zfxtne.fsf@nanos.tec.linutronix.de> From: Alex Shi Message-ID: <87c1cdbc-6af0-3f56-e986-b9df894fe4da@linux.alibaba.com> Date: Tue, 4 Feb 2020 18:18:04 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <87r1zfxtne.fsf@nanos.tec.linutronix.de> Content-Type: text/plain; charset=gbk Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ÔÚ 2020/2/1 ÉÏÎç4:23, Thomas Gleixner дµÀ: > Davidlohr Bueso writes: >> On Tue, 21 Jan 2020, Alex Shi wrote: > > Subject: locking/rtmutex: remove unused cmpxchg_relaxed > > should be > > Subject: locking/rtmutex: Remove unused rt_mutex_cmpxchg_relaxed() > > You're not removing cmpxchg_relaxed, right? > >>> No one use this macro after it was introduced. Better to remove it? > > Please make that factual. > > The macro was never used at all. Remove it. > >> You also need to remove it for the CONFIG_DEBUG_RT_MUTEXES=y case. > > Yes. > >> Hmm unrelated, but do we want CCAS for rtmutex fastpath? Ie: >> >> (l->owner == c && cmpxchg_acquire(&l->owner, c, n) == c) >> >> That would optimize for the contended case and avoid the cmpxchg - it would >> also help if we ever do the top-waiter spin thing. > > Not sure if it buys much, but it kinda makes sense. > > Thanks, > > tglx > Thanks Thomas and David! Is this following patch ok? Thanks Alex --- >From 4cf9e38a73c67c6894f3addb2ddca26bb51b1a28 Mon Sep 17 00:00:00 2001 From: Alex Shi Date: Tue, 21 Jan 2020 15:03:33 +0800 Subject: [PATCH v2] locking/rtmutex: optimize rt_mutex_cmpxchg_xxx series func rt_mutex_cmpxchg_relexed isn't interested by anyone, so remove it. And Davidlohr Bueso suggests check l->owner before cmpxchg to reduce lock contention. Signed-off-by: Alex Shi Cc: Thomas Gleixner Cc: Davidlohr Bueso Cc: Ingo Molnar Cc: Will Deacon Cc: linux-kernel@vger.kernel.org --- kernel/locking/rtmutex.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 851bbb10819d..eb26f4e57ce4 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -141,9 +141,10 @@ static void fixup_rt_mutex_waiters(struct rt_mutex *lock) * set up. */ #ifndef CONFIG_DEBUG_RT_MUTEXES -# define rt_mutex_cmpxchg_relaxed(l,c,n) (cmpxchg_relaxed(&l->owner, c, n) == c) -# define rt_mutex_cmpxchg_acquire(l,c,n) (cmpxchg_acquire(&l->owner, c, n) == c) -# define rt_mutex_cmpxchg_release(l,c,n) (cmpxchg_release(&l->owner, c, n) == c) +# define rt_mutex_cmpxchg_acquire(l,c,n) \ + (l->owner == c && cmpxchg_acquire(&l->owner, c, n) == c) +# define rt_mutex_cmpxchg_release(l,c,n) \ + (l->owner == c && cmpxchg_release(&l->owner, c, n) == c) /* * Callers must hold the ->wait_lock -- which is the whole purpose as we force @@ -202,7 +203,6 @@ static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock, } #else -# define rt_mutex_cmpxchg_relaxed(l,c,n) (0) # define rt_mutex_cmpxchg_acquire(l,c,n) (0) # define rt_mutex_cmpxchg_release(l,c,n) (0) -- 1.8.3.1