From patchwork Thu Jan 20 13:08:12 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "H.J. Lu" X-Patchwork-Id: 50278 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 4792F3857C76 for ; Thu, 20 Jan 2022 13:08:37 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 4792F3857C76 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1642684117; bh=qBs9yr46qE+3lSLkqsRh0VflDJYvpE15jlIWdxn0StY=; h=Date:To:Subject:References:In-Reply-To:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To: From; b=PfWWmE/zCXhaLxnOdGZ5iVlyd81A1UWtvIrppWckBzVgw9JYHEzoqvxRniR53/6JF /7LeeqCt+TBHns+wvSMcbA2moUJt+OMB6V7w2Lemt1KwV/jdOoull6B2gtSn1/Nrd6 yhLs/H/RYfOJ7HEqd+qMPegAb0U1cPXUz72EIB/U= X-Original-To: libc-alpha@sourceware.org Delivered-To: libc-alpha@sourceware.org Received: from mail-pg1-x52c.google.com (mail-pg1-x52c.google.com [IPv6:2607:f8b0:4864:20::52c]) by sourceware.org (Postfix) with ESMTPS id E266B3858D37 for ; Thu, 20 Jan 2022 13:08:15 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org E266B3858D37 Received: by mail-pg1-x52c.google.com with SMTP id 187so5134535pga.10 for ; Thu, 20 Jan 2022 05:08:15 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=qBs9yr46qE+3lSLkqsRh0VflDJYvpE15jlIWdxn0StY=; b=fNtRifjT6slpN/ZkaEnxkQPOYmqEox5OkIjeuC0f7c2kiEhWZ6e6piYvemp0A8/k2M gtTrJKWmr9Dwm4hCNv74bjbtPX+0iAOt0GLhSrxWnpKufp/uE7FrYMghpLKvjiXHmOd6 9UVGI60c/mxf8lDvzDj3QSnCSkPl3qp34AVEkHlFBH9I0QU29+qfBcM6/Dm7v5EmfcYW G6WPPoLWUXKG0VGY8m1akhDWyLH4WYWOHUw6KXrataT6NKJuD/q1IChjEz6hcFSv7PSn 7fMDesLp155qxk6AJFNsw8DsjXrsPFnu9VTWUNL3XorI8zECJDnQnffoa5lus4IurDnU MNgQ== X-Gm-Message-State: AOAM533OLXNv/ZnFZkLuMfjgD7cAU8IdAog8FwsulXYwgkXllc1I7Pfh X9bxCnmE8beNXtW5UyhGDgeTbwzAk/w= X-Google-Smtp-Source: ABdhPJzSX8lpUsgsjegxAcov4IRLzFMdil2SX6PHUYELmw2N7sVyZeiYtjyDQoDn4k1IiFx7jv+4FA== X-Received: by 2002:a63:81c3:: with SMTP id t186mr16639744pgd.127.1642684094939; Thu, 20 Jan 2022 05:08:14 -0800 (PST) Received: from gnu-tgl-3.localdomain ([172.58.35.133]) by smtp.gmail.com with ESMTPSA id s17sm3542835pfg.146.2022.01.20.05.08.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Jan 2022 05:08:14 -0800 (PST) Received: by gnu-tgl-3.localdomain (Postfix, from userid 1000) id E5D85C0537; Thu, 20 Jan 2022 05:08:12 -0800 (PST) Date: Thu, 20 Jan 2022 05:08:12 -0800 To: Jangwoong Kim <6812skiii@gmail.com>, GNU C Library Subject: [PATCH v4] nptl: Effectively skip CAS in spinlock loop Message-ID: References: <20211214123051.800-1-6812skiii@gmail.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Spam-Status: No, score=-3028.8 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" Errors-To: libc-alpha-bounces+patchwork=sourceware.org@sourceware.org Sender: "Libc-alpha" On Thu, Jan 20, 2022 at 04:53:27AM -0800, H.J. Lu wrote: > On Tue, Dec 14, 2021 at 4:31 AM Jangwoong Kim via Libc-alpha > wrote: > > > > 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 | 5 +---- > > 1 file changed, 1 insertion(+), 4 deletions(-) > > > > diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c > > index 47b88a6b5b..06274c68e4 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 (LLL_MUTEX_READ_LOCK (mutex) != 0 || LLL_MUTEX_TRYLOCK (mutex) != 0) > > { > > if (cnt++ >= max_cnt) > > { > > @@ -146,10 +146,7 @@ PTHREAD_MUTEX_LOCK (pthread_mutex_t *mutex) > > break; > > } > > atomic_spin_nop (); > > - if (LLL_MUTEX_READ_LOCK (mutex) != 0) > > - continue; > > } > > - while (LLL_MUTEX_TRYLOCK (mutex) != 0); > > > > mutex->__data.__spins += (cnt - mutex->__data.__spins) / 8; > > } > > -- > > 2.25.1 > > > > LGTM. > > Reviewed-by: H.J. Lu > > Thanks. > This is the v4 patch I am checkinng in. H.J. --- From: Jangwoong Kim <6812skiii@gmail.com> Date: Tue, 14 Dec 2021 21:30:51 +0900 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. Reviewed-by: H.J. Lu --- nptl/pthread_mutex_lock.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c index 31dfc7f1d7..d2e652d151 100644 --- a/nptl/pthread_mutex_lock.c +++ b/nptl/pthread_mutex_lock.c @@ -146,10 +146,9 @@ PTHREAD_MUTEX_LOCK (pthread_mutex_t *mutex) break; } atomic_spin_nop (); - if (LLL_MUTEX_READ_LOCK (mutex) != 0) - continue; } - while (LLL_MUTEX_TRYLOCK (mutex) != 0); + while (LLL_MUTEX_READ_LOCK (mutex) != 0 + || LLL_MUTEX_TRYLOCK (mutex) != 0); mutex->__data.__spins += (cnt - mutex->__data.__spins) / 8; }