Date: Fri, 5 Jun 2015 08:11:48 +0000 (GMT) From: jenkins-admin@freebsd.org To: jenkins-admin@FreeBSD.org, freebsd-current@freebsd.org Subject: FreeBSD_HEAD-tests - Build #1083 - Fixed Message-ID: <1160690749.52.1433491908728.JavaMail.jenkins@jenkins-9.freebsd.org> In-Reply-To: <2030674114.50.1433460982630.JavaMail.jenkins@jenkins-9.freebsd.org> References: <2030674114.50.1433460982630.JavaMail.jenkins@jenkins-9.freebsd.org>
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FreeBSD_HEAD-tests - Build #1083 - Fixed: Check console output at https://jenkins.freebsd.org/job/FreeBSD_HEAD-tests/1083/ to view the results. From owner-freebsd-current@FreeBSD.ORG Fri Jun 5 11:38:22 2015 Return-Path: <owner-freebsd-current@FreeBSD.ORG> Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 48D05A76 for <freebsd-current@freebsd.org>; Fri, 5 Jun 2015 11:38:22 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id CEE11133A for <freebsd-current@freebsd.org>; Fri, 5 Jun 2015 11:38:21 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kostik@localhost [127.0.0.1]) by kib.kiev.ua (8.14.9/8.14.9) with ESMTP id t55BcGSO064884 (version=TLSv1/SSLv3 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO); Fri, 5 Jun 2015 14:38:16 +0300 (EEST) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.9.2 kib.kiev.ua t55BcGSO064884 Received: (from kostik@localhost) by tom.home (8.14.9/8.14.9/Submit) id t55BcGe5064883; Fri, 5 Jun 2015 14:38:16 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Fri, 5 Jun 2015 14:38:16 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Hans Petter Selasky <hps@selasky.org> Cc: FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: [CFR] Replacing while loops with proper division and multiplication Message-ID: <20150605113816.GB2499@kib.kiev.ua> References: <55714B26.6060802@selasky.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55714B26.6060802@selasky.org> User-Agent: Mutt/1.5.23 (2014-03-12) 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: freebsd-current@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Discussions about the use of FreeBSD-current <freebsd-current.freebsd.org> List-Unsubscribe: <http://lists.freebsd.org/mailman/options/freebsd-current>, <mailto:freebsd-current-request@freebsd.org?subject=unsubscribe> List-Archive: <http://lists.freebsd.org/pipermail/freebsd-current/>; List-Post: <mailto:freebsd-current@freebsd.org> List-Help: <mailto:freebsd-current-request@freebsd.org?subject=help> List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>, <mailto:freebsd-current-request@freebsd.org?subject=subscribe> X-List-Received-Date: Fri, 05 Jun 2015 11:38:22 -0000 On Fri, Jun 05, 2015 at 09:09:26AM +0200, Hans Petter Selasky wrote: > Hi, > > I was going through some timer code and found some unnecessary while > loops in kern/kern_clocksource.c . > > I added some prints and found that during boot, "runs" can exceed 2000, > while during regular usage runs is typically 1. Do you think it is worth > to convert these loops into division and multiplications? It might make > the CPU pipeline a tiny bit faster, having to skip some conditionals? > And also possibly improve readability? For typical loop count of one, I think that setup time for the division is much greater than single substraction and non-taken conditional jump, which is also should be consistently predicted as not taken. You could try to run a microbenchmark to see if the patch makes any sense.
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