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Wed, 27 Jan 2021 20:01:25 +0000 X-MS-Exchange-Authentication-Results: spf=pass (sender IP is 131.228.2.8) smtp.mailfrom=nokia.com; lists.infradead.org; dkim=none (message not signed) header.d=none;lists.infradead.org; dmarc=pass action=none header.from=nokia.com; Received-SPF: Pass (protection.outlook.com: domain of nokia.com designates 131.228.2.8 as permitted sender) receiver=protection.outlook.com; client-ip=131.228.2.8; helo=fihe3nok0734.emea.nsn-net.net; Received: from fihe3nok0734.emea.nsn-net.net (131.228.2.8) by AM5EUR03FT004.mail.protection.outlook.com (10.152.16.163) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3784.11 via Frontend Transport; Wed, 27 Jan 2021 20:01:25 +0000 Received: from ulegcparamis.emea.nsn-net.net (ulegcparamis.emea.nsn-net.net [10.151.74.146]) by fihe3nok0734.emea.nsn-net.net (GMO) with ESMTP id 10RK1NYh025069; Wed, 27 Jan 2021 20:01:23 GMT From: Alexander A Sverdlin To: Peter Zijlstra , Ingo Molnar , Will Deacon , linux-kernel@vger.kernel.org Cc: Alexander Sverdlin , Russell King , linux-arm-kernel@lists.infradead.org Subject: [PATCH 1/2] qspinlock: Ensure writes are pushed out of core write buffer Date: Wed, 27 Jan 2021 21:01:08 +0100 Message-Id: <20210127200109.16412-1-alexander.sverdlin@nokia.com> X-Mailer: git-send-email 2.10.2 X-EOPAttributedMessage: 0 X-MS-Office365-Filtering-HT: Tenant X-MS-PublicTrafficType: Email MIME-Version: 1.0 Content-Type: text/plain X-MS-Office365-Filtering-Correlation-Id: f4c6351d-9918-46ec-b02d-08d8c2fe53dc X-MS-TrafficTypeDiagnostic: VI1PR07MB3470: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:7691; 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X-OriginatorOrg: nokia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Jan 2021 20:01:25.6779 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: f4c6351d-9918-46ec-b02d-08d8c2fe53dc X-MS-Exchange-CrossTenant-Id: 5d471751-9675-428d-917b-70f44f9630b0 X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=5d471751-9675-428d-917b-70f44f9630b0;Ip=[131.228.2.8];Helo=[fihe3nok0734.emea.nsn-net.net] X-MS-Exchange-CrossTenant-AuthSource: AM5EUR03FT004.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI1PR07MB3470 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Alexander Sverdlin Ensure writes are pushed out of core write buffer to prevent waiting code on another cores from spinning longer than necessary. 6 threads running tight spinlock loop competing for the same lock on 6 cores on MIPS/Octeon do 1000000 iterations... before the patch in: 4.3 sec after the patch in: 1.2 sec Same 6-core Octeon machine: sysbench --test=mutex --num-threads=64 --memory-scope=local run w/o patch: 1.53s with patch: 1.28s This will also allow to remove the smp_wmb() in arch/arm/include/asm/mcs_spinlock.h (was it actually addressing the same issue?). Finally our internal quite diverse test suite of different IPC/network aspects didn't detect any regressions on ARM/ARM64/x86_64. Signed-off-by: Alexander Sverdlin --- kernel/locking/mcs_spinlock.h | 5 +++++ kernel/locking/qspinlock.c | 6 ++++++ 2 files changed, 11 insertions(+) diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h index 5e10153..10e497a 100644 --- a/kernel/locking/mcs_spinlock.h +++ b/kernel/locking/mcs_spinlock.h @@ -89,6 +89,11 @@ void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node) return; } WRITE_ONCE(prev->next, node); + /* + * This is necessary to make sure that the corresponding "while" in the + * mcs_spin_unlock() doesn't loop forever + */ + smp_wmb(); /* Wait until the lock holder passes the lock down. */ arch_mcs_spin_lock_contended(&node->locked); diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index cbff6ba..577fe01 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -469,6 +469,12 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) /* Link @node into the waitqueue. */ WRITE_ONCE(prev->next, node); + /* + * This is necessary to make sure that the corresponding + * smp_cond_load_relaxed() below (running on another core) + * doesn't spin forever. + */ + smp_wmb(); pv_wait_node(node, prev); arch_mcs_spin_lock_contended(&node->locked); -- 2.10.2 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=-17.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT 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 C3F97C433DB for ; Wed, 27 Jan 2021 20:02:50 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 81F8F64DA3 for ; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org From: Alexander Sverdlin Ensure writes are pushed out of core write buffer to prevent waiting code on another cores from spinning longer than necessary. 6 threads running tight spinlock loop competing for the same lock on 6 cores on MIPS/Octeon do 1000000 iterations... before the patch in: 4.3 sec after the patch in: 1.2 sec Same 6-core Octeon machine: sysbench --test=mutex --num-threads=64 --memory-scope=local run w/o patch: 1.53s with patch: 1.28s This will also allow to remove the smp_wmb() in arch/arm/include/asm/mcs_spinlock.h (was it actually addressing the same issue?). Finally our internal quite diverse test suite of different IPC/network aspects didn't detect any regressions on ARM/ARM64/x86_64. Signed-off-by: Alexander Sverdlin --- kernel/locking/mcs_spinlock.h | 5 +++++ kernel/locking/qspinlock.c | 6 ++++++ 2 files changed, 11 insertions(+) diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h index 5e10153..10e497a 100644 --- a/kernel/locking/mcs_spinlock.h +++ b/kernel/locking/mcs_spinlock.h @@ -89,6 +89,11 @@ void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node) return; } WRITE_ONCE(prev->next, node); + /* + * This is necessary to make sure that the corresponding "while" in the + * mcs_spin_unlock() doesn't loop forever + */ + smp_wmb(); /* Wait until the lock holder passes the lock down. */ arch_mcs_spin_lock_contended(&node->locked); diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index cbff6ba..577fe01 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -469,6 +469,12 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) /* Link @node into the waitqueue. */ WRITE_ONCE(prev->next, node); + /* + * This is necessary to make sure that the corresponding + * smp_cond_load_relaxed() below (running on another core) + * doesn't spin forever. + */ + smp_wmb(); pv_wait_node(node, prev); arch_mcs_spin_lock_contended(&node->locked); -- 2.10.2 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel