From patchwork Wed Nov 10 00:16:14 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "H.J. Lu" X-Patchwork-Id: 47342 Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id E63643857C4B for ; Wed, 10 Nov 2021 00:19:47 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org E63643857C4B DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1636503587; bh=4h04qgwOtsVHEm2XST+J6XAxLFcZdm/Q3FHtH/yruSk=; h=To:Subject:Date:In-Reply-To:References:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc: From; b=Eqcy5l2oZanHEyzQbW6zjmN6DZnVvUSka3zYVSdi8qWAgh6MN9nei3h4Jhi6+UKFc 3pRcESy9z0UiwdVCugG01xho1qBqA0vUlc7zCW4bA5Vh4jv9QQP7C09dwg0kRa2ZJc Rd1a4ZA8O2lUn5lVpDYdi8y4zPtVF5M8FdqKwIfI= X-Original-To: libc-alpha@sourceware.org Delivered-To: libc-alpha@sourceware.org Received: from mail-pf1-x432.google.com (mail-pf1-x432.google.com [IPv6:2607:f8b0:4864:20::432]) by sourceware.org (Postfix) with ESMTPS id E5A083858033 for ; Wed, 10 Nov 2021 00:16:16 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org E5A083858033 Received: by mail-pf1-x432.google.com with SMTP id g18so989176pfk.5 for ; Tue, 09 Nov 2021 16:16:16 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=4h04qgwOtsVHEm2XST+J6XAxLFcZdm/Q3FHtH/yruSk=; b=q3rzN2pgn11gN6VftRXuxhDLASV+kSzP5Qyhj40c81cLXhZB0iElasth79c3cb42TF 2FNUtLjZBhRJd60ytcYWmFK9uAOjcyMiG8NLOIZPuASs9SPAxe3bs+5oZB+vvbMATAMJ 9EgLNc3p0Vw9Fovbs1ZdncxnMzT7WP8NwtGySseH/gL5RTokqQ/0Rx7wfLTR9VEv8q8n HBE9Pzqt07iClqP1nHWn9DF9ntb+bMJ3rmGonKaNjU4cDe8x3UG4VkPsq5MXhAvXWZHK GDUfAFzwQSG33Agv2xWnwSVJvLcyZCqfncfMrvUaVCx6y4HxRbRaIDCHOgvJmQm09fpj ZX4Q== X-Gm-Message-State: AOAM531qHMdO4Asl23PoZ0rO9JVOefDUrXyzd4b6gi4imJuu3ppYxjPT 1IczcOwmT7CpFYaabMM+bypiJ7yJ+ww= X-Google-Smtp-Source: ABdhPJzULfLMGtzqAUSASw1A67BHDOcOX6Z5KHsXIuBqvTuQdgS/yn+P6HD1ZfMKIUncGf9ledTG+A== X-Received: by 2002:a63:5151:: with SMTP id r17mr9170924pgl.56.1636503376096; Tue, 09 Nov 2021 16:16:16 -0800 (PST) Received: from gnu-cfl-2.localdomain ([172.58.35.133]) by smtp.gmail.com with ESMTPSA id g17sm2410368pfv.136.2021.11.09.16.16.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Nov 2021 16:16:15 -0800 (PST) Received: from gnu-cfl-2.lan (localhost [IPv6:::1]) by gnu-cfl-2.localdomain (Postfix) with ESMTP id 8C31E1A0ED2; Tue, 9 Nov 2021 16:16:14 -0800 (PST) To: libc-alpha@sourceware.org Subject: [PATCH v4 3/3] Optimize CAS in __pthread_mutex_lock_full [BZ #28537] Date: Tue, 9 Nov 2021 16:16:14 -0800 Message-Id: <20211110001614.2087610-4-hjl.tools@gmail.com> X-Mailer: git-send-email 2.33.1 In-Reply-To: <20211110001614.2087610-1-hjl.tools@gmail.com> References: <20211110001614.2087610-1-hjl.tools@gmail.com> MIME-Version: 1.0 X-Spam-Status: No, score=-3030.0 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, GIT_PATCH_0, RCVD_IN_BARRACUDACENTRAL, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Patchwork-Original-From: "H.J. Lu via Libc-alpha" From: "H.J. Lu" Reply-To: "H.J. Lu" Cc: Florian Weimer , Arjan van de Ven , Andreas Schwab Errors-To: libc-alpha-bounces+patchwork=sourceware.org@sourceware.org Sender: "Libc-alpha" 1. Do an atomic load and skip CAS if compare may fail to reduce cache line bouncing on contended locks. 2. Replace atomic_compare_and_exchange_bool_acq with atomic_compare_and_exchange_val_acq to avoid the extra load. --- nptl/pthread_mutex_lock.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c index 1126ecba95..9a18073f29 100644 --- a/nptl/pthread_mutex_lock.c +++ b/nptl/pthread_mutex_lock.c @@ -309,12 +309,17 @@ __pthread_mutex_lock_full (pthread_mutex_t *mutex) meantime. */ if ((oldval & FUTEX_WAITERS) == 0) { - if (atomic_compare_and_exchange_bool_acq (&mutex->__data.__lock, - oldval | FUTEX_WAITERS, - oldval) - != 0) + int currval = atomic_load_relaxed (&mutex->__data.__lock); + if (currval != oldval) + { + oldval = currval; + continue; + } + int newval = atomic_compare_and_exchange_val_acq + (&mutex->__data.__lock, oldval | FUTEX_WAITERS, oldval); + if (newval != oldval) { - oldval = mutex->__data.__lock; + oldval = newval; continue; } oldval |= FUTEX_WAITERS;