From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: <6812skiii@gmail.com> Received: from mail-pj1-x1033.google.com (mail-pj1-x1033.google.com [IPv6:2607:f8b0:4864:20::1033]) by sourceware.org (Postfix) with ESMTPS id A24843858D28 for ; Tue, 14 Dec 2021 11:01:34 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org A24843858D28 Received: by mail-pj1-x1033.google.com with SMTP id gj24so100988pjb.0 for ; Tue, 14 Dec 2021 03:01:34 -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:mime-version :content-transfer-encoding; bh=YP11M/3qEbQRafB1e77UVz6AIzsqK8XBhAnjrD7ocsw=; b=uY6y2L0/pL5f3DHNumnsuK7gIhG81Sbc1ZWWHIrYu8IYccWO3xcrdegvyI+fIbjG6H 1vwXpFoxr/bFSYBVSTaIGR1cZGBZ4uPq5JPnZSRlyzeIMbepMxbN5XdzhHkCX5PNaPid mToyh4QpiTvj9p514wWajCuSdyx5J9Hfymvnbo2QEiI2TadPGiwx1x+Ht/iKJiDpvuPl +cVEobAAlOnxByIHpTwm201mHzLK56gThskdzKvEBLZhCpZsD+lF08ECInsBnL7pQtRv k/sUTPF5T7P0ss/q8yxNNthZl//zzjull+7sipvMPqNEQkd0vbp+yGtx7m4mN4ndL5tN vbJQ== X-Gm-Message-State: AOAM530wHm4Mt6ZtsqKODDHlY59e/4+jpFRhzzlPoyy7a2+KrmzhseDF L/o6Olv3nfngz2NT4rolAWRdLekKGGbETg== X-Google-Smtp-Source: ABdhPJznjRrS4cs/8cseTsRoOHd3GBXvUfFs/qiZ/iyibGjbnqhnwz6kZ/SUkjReJu/NRdsbvmLsNw== X-Received: by 2002:a17:90b:357:: with SMTP id fh23mr4838969pjb.238.1639479693667; Tue, 14 Dec 2021 03:01:33 -0800 (PST) Received: from DESKTOP-OO3QD6O.localdomain ([221.162.118.197]) by smtp.gmail.com with ESMTPSA id d4sm15373571pfj.78.2021.12.14.03.01.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Dec 2021 03:01:33 -0800 (PST) From: Jangwoong Kim <6812skiii@gmail.com> To: libc-alpha@sourceware.org Cc: Jangwoong Kim <6812skiii@gmail.com> Subject: [PATCH v2] nptl: Effectively skip CAS in spinlock loop Date: Tue, 14 Dec 2021 20:01:19 +0900 Message-Id: <20211214110119.592-1-6812skiii@gmail.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-12.2 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, FROM_STARTS_WITH_NUMS, GIT_PATCH_0, 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-List-Received-Date: Tue, 14 Dec 2021 11:01:36 -0000 The commit: "Add LLL_MUTEX_READ_LOCK [BZ #28537]" SHA1: d672a98a1af106bd68deb15576710cd61363f7a6 introduced LLL_MUTEX_READ_LOCK, to skip CAS in spinlock loop if atomic load fails. But, "continue" inside of do-while loop does not skip the evaluation of escape expression, thus CAS is not skipped. Replace do-while with while and skip LLL_MUTEX_TRYLOCK if LLL_MUTEX_READ_LOCK fails. --- nptl/pthread_mutex_lock.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c index 47b88a6b5b..3ad199a5e1 100644 --- a/nptl/pthread_mutex_lock.c +++ b/nptl/pthread_mutex_lock.c @@ -138,7 +138,7 @@ PTHREAD_MUTEX_LOCK (pthread_mutex_t *mutex) int cnt = 0; int max_cnt = MIN (max_adaptive_count (), mutex->__data.__spins * 2 + 10); - do + while (1) { if (cnt++ >= max_cnt) { @@ -146,10 +146,9 @@ PTHREAD_MUTEX_LOCK (pthread_mutex_t *mutex) break; } atomic_spin_nop (); - if (LLL_MUTEX_READ_LOCK (mutex) != 0) - continue; + if (LLL_MUTEX_READ_LOCK (mutex) == 0 && LLL_MUTEX_TRYLOCK (mutex) == 0) + break; } - while (LLL_MUTEX_TRYLOCK (mutex) != 0); mutex->__data.__spins += (cnt - mutex->__data.__spins) / 8; } -- 2.25.1