From patchwork Thu Apr 26 10:34:23 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Will Deacon X-Patchwork-Id: 134475 Delivered-To: patch@linaro.org Received: by 10.46.151.6 with SMTP id r6csp2080581lji; Thu, 26 Apr 2018 03:35:40 -0700 (PDT) X-Google-Smtp-Source: AIpwx4/jgnd0K1pvtO2YTEIkl3nR5JC/hC2+r954DbldB4qCLZpt17B36/oRdx84DeVBw3+NLdAO X-Received: by 2002:a17:902:5602:: with SMTP id h2-v6mr30607970pli.115.1524738940236; Thu, 26 Apr 2018 03:35:40 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1524738940; cv=none; d=google.com; s=arc-20160816; b=XCGP+vNCMRfYMOg0V4oJhJTvfgwu/t7oIPsMJEtwfNaMIA47Q/0eKKPHr1h3rJORH2 wI3QJfzYEhp4aJ5ZdBRQCHbeGTdfFcDA5a4+gc1toRNxbRIJZ2QNvJRginOFvnW4bDsC l8jSE77hykxQN5+UWNZD1OD0fVUc0+I0eUwVzfOlB5vdS6/Fff+j+hnb6nuWqcuURWrq fnbxoNiXhFgu6mj6og2IDOPXVYQ2H/6smMN85wT0SdsK/0Noy8NGajvXyBvWhekc1cdh BY1YwcsWOBgu2H0rxcTxsnFZBctIjT/TtdkawlOrMETZsIdwBHvl0Fl4USGRq9XxWIQh bO0g== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:references:in-reply-to:message-id:date :subject:cc:to:from:arc-authentication-results; bh=4MQhOO1+AA8rmTSqhaSD7GxCnAmqykwMxorLeKJlh9g=; b=zKfR1XdrtdmDuPOPZ9gCcWmZcAGW5OcAUjam67xNFAa77aHF2wHcDS5aw4uyJufcQe xyiZfBI9SQ6Sb8zjtyDcfQzj4XPFcsSRAkjCjryRHIXpiNQlpA3Hu/APQFRA8J3kScXh gzF9f6ymkrdWi2jGogIOl5oGFAhMkGuQXcdCjN76DP+9uLz4wbvntKlTh+zijk/n05jS gbj3/5GDUwBFur1QsYwyz/A0JmTx1Hq5Q+qXzOy5jC8Tk54hteA8ORjSnaYvNeNf2v7X QjigP59U8vyaDax7IuzylBkQmmI1tczRmwDJj8xlltFYgqtNEi0uMV8OXpc5S/10L7IQ H3Ww== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Return-Path: Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67]) by mx.google.com with ESMTP id v6si460746pgs.399.2018.04.26.03.35.39; Thu, 26 Apr 2018 03:35:40 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755755AbeDZKfg (ORCPT + 29 others); Thu, 26 Apr 2018 06:35:36 -0400 Received: from foss.arm.com ([217.140.101.70]:51126 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755164AbeDZKeL (ORCPT ); Thu, 26 Apr 2018 06:34:11 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6D9F8174E; Thu, 26 Apr 2018 03:34:10 -0700 (PDT) Received: from edgewater-inn.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 3FCEC3F7BE; Thu, 26 Apr 2018 03:34:10 -0700 (PDT) Received: by edgewater-inn.cambridge.arm.com (Postfix, from userid 1000) id 7C6201AE516A; Thu, 26 Apr 2018 11:34:29 +0100 (BST) From: Will Deacon To: linux-kernel@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org, peterz@infradead.org, mingo@kernel.org, boqun.feng@gmail.com, paulmck@linux.vnet.ibm.com, longman@redhat.com, will.deacon@arm.com Subject: [PATCH v3 09/14] locking/qspinlock: Use smp_cond_load_relaxed to wait for next node Date: Thu, 26 Apr 2018 11:34:23 +0100 Message-Id: <1524738868-31318-10-git-send-email-will.deacon@arm.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1524738868-31318-1-git-send-email-will.deacon@arm.com> References: <1524738868-31318-1-git-send-email-will.deacon@arm.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When a locker reaches the head of the queue and takes the lock, a concurrent locker may enqueue and force the lock holder to spin whilst its node->next field is initialised. Rather than open-code a READ_ONCE/cpu_relax() loop, this can be implemented using smp_cond_load_relaxed instead. Cc: Peter Zijlstra Cc: Ingo Molnar Signed-off-by: Will Deacon --- kernel/locking/qspinlock.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) -- 2.1.4 diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 5e383cfe4cce..7b8c81ebb15e 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -483,10 +483,8 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) /* * contended path; wait for next if not observed yet, release. */ - if (!next) { - while (!(next = READ_ONCE(node->next))) - cpu_relax(); - } + if (!next) + next = smp_cond_load_relaxed(&node->next, (VAL)); arch_mcs_spin_unlock_contended(&next->locked); pv_kick_node(lock, next);