From owner-svn-src-all@freebsd.org Mon Jan 30 10:53:50 2017 Return-Path: <owner-svn-src-all@freebsd.org> Delivered-To: svn-src-all@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 8CD69CC8285; Mon, 30 Jan 2017 10:53:50 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 0A8991061; Mon, 30 Jan 2017 10:53:49 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kib@localhost [127.0.0.1]) by kib.kiev.ua (8.15.2/8.15.2) with ESMTPS id v0UArjDG071806 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Mon, 30 Jan 2017 12:53:45 +0200 (EET) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua v0UArjDG071806 Received: (from kostik@localhost) by tom.home (8.15.2/8.15.2/Submit) id v0UArjhG071805; Mon, 30 Jan 2017 12:53:45 +0200 (EET) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Mon, 30 Jan 2017 12:53:45 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Justin Hibbits <jhibbits@FreeBSD.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r312973 - head/sys/powerpc/include Message-ID: <20170130105345.GL3018@kib.kiev.ua> References: <201701300215.v0U2Fsl0006455@repo.freebsd.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201701300215.v0U2Fsl0006455@repo.freebsd.org> User-Agent: Mutt/1.7.2 (2016-11-26) X-Spam-Status: No, score=-2.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FREEMAIL_FROM,NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.1 X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on tom.home X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" <svn-src-all.freebsd.org> List-Unsubscribe: <https://lists.freebsd.org/mailman/options/svn-src-all>, <mailto:svn-src-all-request@freebsd.org?subject=unsubscribe> List-Archive: <http://lists.freebsd.org/pipermail/svn-src-all/> List-Post: <mailto:svn-src-all@freebsd.org> List-Help: <mailto:svn-src-all-request@freebsd.org?subject=help> List-Subscribe: <https://lists.freebsd.org/mailman/listinfo/svn-src-all>, <mailto:svn-src-all-request@freebsd.org?subject=subscribe> X-List-Received-Date: Mon, 30 Jan 2017 10:53:50 -0000 > +#ifdef __GNUCLIKE_ASM > + __asm __volatile ( > + "1:\tlwarx %0, 0, %3\n\t" /* load old value */ > + "cmplw %4, %0\n\t" /* compare */ > + "bne 2f\n\t" /* exit if not equal */ > + "stwcx. %5, 0, %3\n\t" /* attempt to store */ > + "bne- 1b\n\t" /* spin if failed */ > + "li %0, 1\n\t" /* success - retval = 1 */ > + "b 3f\n\t" /* we've succeeded */ > + "2:\n\t" > + "stwcx. %0, 0, %3\n\t" /* clear reservation (74xx) */ > + "stwx %0, 0, %7\n\t" > + "li %0, 0\n\t" /* failure - retval = 0 */ > + "3:\n\t" > + : "=&r" (ret), "=m" (*p), "=m" (*cmpval) > + : "r" (p), "r" (*cmpval), "r" (newval), "m" (*p), "r"(cmpval) > + : "cr0", "memory"); > +#endif It seems that in case of failed conditional store, the code retries. Note that this is not incorrect but also not a desirable behaviour with fcmpset: the function should return error and leave the retry to the caller. There is no point in having embedded loop.