From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ej1-x629.google.com (mail-ej1-x629.google.com [IPv6:2a00:1450:4864:20::629]) by sourceware.org (Postfix) with ESMTPS id E9F963858C53; Thu, 29 Sep 2022 00:11:09 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org E9F963858C53 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=gmail.com Received: by mail-ej1-x629.google.com with SMTP id lh5so30319763ejb.10; Wed, 28 Sep 2022 17:11:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date; bh=6ZprzVddDs8Zkz3D0PT3glt0jPFXa5dO0cGWo/winvU=; b=Ln1ka+coLq6/a5uCfuDbbuhGUXu4LZH4lc0WBKpQAq8ujnupchqkTyajIZWCinUmxH LYWPRTemn2F8+VL3bjIDD9Rw/0EX7ODgEOn5JBdu3bEFkWiRLQ3QVl7zwtCuI1E31P8I AxU9DdvJxWym7g+KijfE0UhZVHZtF2xMblJN1Ip14YNuVoCHVaMGDPs3MScNlWdcYG14 srxJ0AY0uPrK+RHFozDwzbDMhg/uleIPxS3dWkc6GLXqQtYhW7ruiYqziZZddxL0ddQ9 6hTnSXj+mqmETabvpqTXpqXDl/C+DcO+rHXnLdoEtpB8UcRgkQProR252Q7N/BnavGm/ n8xA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date; bh=6ZprzVddDs8Zkz3D0PT3glt0jPFXa5dO0cGWo/winvU=; b=w8tiZgh40n0c90tTJkNKk4L2PTt9Izwb1gUmIQ1bQsSNvV9rgbaJ9wIadMblkN6EFu JFu3Q05X+nHukGUTl5z8jsrp2yDD01z2KvgTRsJIA0lhiNO5QcJXfVnAujgpEb9517uz 3pyNiVc62CVvGiiYpu9RFjLjxvg4sgFldBCZgn7rnWUw5xW/n+HRBziDM3F1W6/BM8X5 mXkseqZqAVPfla//HSQPPVf5bI6CwUIYXrCYIhcfLpEwmrWEEW61zmVLqslQqoXFJsCa t2OegxxCaKOes9/ZZK9V47tXh6X06QU5dNJ+nFRDjst4SaPzOUKWyjlMxA1UD+EQRv6w uN/A== X-Gm-Message-State: ACrzQf3qbMjs5XgnUioFoPb6ML/KIesHksi/TF7CaaYwYRTJxo0Cn5sn v0GGXt8nBwhrDkOSrniM6Ye5/18ZkeodVaMGzlI= X-Google-Smtp-Source: AMsMyM6eXdjc7aAM0PRXeP3QiBjE4ouKtcQBN7ZaUpzb0V2BMSkaWlEqYHuufspM6zFHdXa7f1DZFZWvWaNxzgEfo9g= X-Received: by 2002:a17:907:724a:b0:782:3754:ecb3 with SMTP id ds10-20020a170907724a00b007823754ecb3mr393443ejc.282.1664410268850; Wed, 28 Sep 2022 17:11:08 -0700 (PDT) MIME-Version: 1.0 References: <20211111162428.2286605-1-hjl.tools@gmail.com> <20211111162428.2286605-3-hjl.tools@gmail.com> <87zgq9rywl.fsf@igel.home> In-Reply-To: From: Noah Goldstein Date: Wed, 28 Sep 2022 20:10:57 -0400 Message-ID: Subject: Re: [PATCH v6 2/4] Avoid extra load with CAS in __pthread_mutex_lock_full [BZ #28537] To: Sunil Pandey Cc: Andreas Schwab , Libc-stable Mailing List , Florian Weimer , Arjan van de Ven , GNU C Library , "Paul A . Clarke" Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-9.6 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,GIT_PATCH_0,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On Sun, Sep 11, 2022 at 4:17 PM Sunil Pandey via Libc-stable wrote: > > On Fri, Nov 12, 2021 at 10:52 AM Andreas Schwab wrote: > > > > On Nov 11 2021, H.J. Lu wrote: > > > > > diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c > > > index 72058c719c..762059b230 100644 > > > --- a/nptl/pthread_mutex_lock.c > > > +++ b/nptl/pthread_mutex_lock.c > > > @@ -304,12 +304,12 @@ __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 val; > > > + if ((val = atomic_compare_and_exchange_val_acq > > > + (&mutex->__data.__lock, oldval | FUTEX_WAITERS, > > > + oldval)) != oldval) > > > > Please move the assignment out of the condition. > > > > Andreas. > > > > -- > > Andreas Schwab, schwab@linux-m68k.org > > GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510 2552 DF73 E780 A9DA AEC1 > > "And now for something completely different." > > I would like to backport this patch to release branch 2.33 and 2.34 > > Any comments/suggestions or objections on this. > > commit 49302b8fdf9103b6fc0a398678668a22fa19574c > Author: H.J. Lu > Date: Thu Nov 11 06:54:01 2021 -0800 > > Avoid extra load with CAS in __pthread_mutex_clocklock_common [BZ #28537] > > Replace boolean CAS with value CAS to avoid the extra load. > > Reviewed-by: Szabolcs Nagy Fine by me.