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[2620:137:e000::1:20]) by mx.google.com with ESMTP id d7-20020a056a0024c700b0057731e4f614si6706582pfv.85.2022.12.24.04.13.14; Sat, 24 Dec 2022 04:13:28 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=k20201202 header.b=rCS4ejFs; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231130AbiLXMG6 (ORCPT + 99 others); Sat, 24 Dec 2022 07:06:58 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41014 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229507AbiLXMGz (ORCPT ); Sat, 24 Dec 2022 07:06:55 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 80F0D1012 for ; Sat, 24 Dec 2022 04:06:54 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id CEE29601C3 for ; Sat, 24 Dec 2022 12:06:53 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 701E4C433EF; Sat, 24 Dec 2022 12:06:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1671883613; bh=Lbw0POaZnF+kGvgdPds+fH17Q+0WMb3P+5vjsislLY4=; h=From:To:Cc:Subject:Date:From; b=rCS4ejFsUQ32fNYAwoAN9QtpY/7IeI2eDTf0t4iYOrCiGQfRQMI1eS9g8am7GiMGv MBhcp8TzCkv8XzNqXW3uXyrPcX4WujtBYO93189U15ryHlO53Wt9T2dG6/Y/mAk41u q6qtPMqkLtw0CG9A0x8ajNYIfqxn9T/VzuwERXgRmNy9xp36dFhePtUWh1w2NZBQzf 3BMDXTXM9a12B3Q3cELlPAslbYQvCw7hhqAdi4wIRDEDRPnEeyfqd2J+FAYLgn8NPl LAAbABMMZ0rbK5MtnZqV/Bi75OgQJBHk0Jf5Q4K29ZQMlMW2KBaByYecpT2NRvgiwJ +NrQnm1GNOOfQ== From: guoren@kernel.org To: peterz@infradead.org, longman@redhat.com Cc: linux-kernel@vger.kernel.org, guoren@kernel.org, Guo Ren , Boqun Feng , Will Deacon , Ingo Molnar Subject: [PATCH] locking/qspinlock: Optimize pending state waiting for unlock Date: Sat, 24 Dec 2022 07:05:45 -0500 Message-Id: <20221224120545.262989-1-guoren@kernel.org> X-Mailer: git-send-email 2.36.1 MIME-Version: 1.0 X-Spam-Status: No, score=-7.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_HI, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1753097445696348387?= X-GMAIL-MSGID: =?utf-8?q?1753097445696348387?= From: Guo Ren When we're pending, we only care about lock value. The xchg_tail wouldn't affect the pending state. That means the hardware thread could stay in a sleep state and leaves the rest execution units' resources of pipeline to other hardware threads. This optimization may work only for SMT scenarios because the granularity between cores is cache-block. Signed-off-by: Guo Ren Signed-off-by: Guo Ren Cc: Waiman Long Cc: Peter Zijlstra Cc: Boqun Feng Cc: Will Deacon Cc: Ingo Molnar Acked-by: Waiman Long --- kernel/locking/qspinlock.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 2b23378775fe..ebe6b8ec7cb3 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -371,7 +371,7 @@ void __lockfunc queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) /* * We're pending, wait for the owner to go away. * - * 0,1,1 -> 0,1,0 + * 0,1,1 -> *,1,0 * * this wait loop must be a load-acquire such that we match the * store-release that clears the locked bit and create lock @@ -380,7 +380,7 @@ void __lockfunc queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) * barriers. */ if (val & _Q_LOCKED_MASK) - atomic_cond_read_acquire(&lock->val, !(VAL & _Q_LOCKED_MASK)); + smp_cond_load_acquire(&lock->locked, !VAL); /* * take ownership and clear the pending bit.