From owner-svn-src-head@freebsd.org Sat Mar 4 19:43:38 2017 Return-Path: Delivered-To: svn-src-head@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 08EB6CF7DCB; Sat, 4 Mar 2017 19:43:38 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from mail.baldwin.cx (bigwig.baldwin.cx [IPv6:2001:470:1f11:75::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 DC2191E29; Sat, 4 Mar 2017 19:43:37 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from ralph.baldwin.cx (c-73-231-226-104.hsd1.ca.comcast.net [73.231.226.104]) by mail.baldwin.cx (Postfix) with ESMTPSA id D978910A791; Sat, 4 Mar 2017 14:43:36 -0500 (EST) From: John Baldwin To: Pedro Giffuni Cc: Slawa Olhovchenkov , src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r314669 - head/sys/i386/conf Date: Sat, 04 Mar 2017 11:43:06 -0800 Message-ID: <2368011.hGEX4V32U5@ralph.baldwin.cx> User-Agent: KMail/4.14.10 (FreeBSD/11.0-STABLE; KDE/4.14.10; amd64; ; ) In-Reply-To: References: <201703041504.v24F4HMh023937@repo.freebsd.org> <20170304153228.GM15630@zxy.spb.ru> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.4.3 (mail.baldwin.cx); Sat, 04 Mar 2017 14:43:36 -0500 (EST) X-Virus-Scanned: clamav-milter 0.99.2 at mail.baldwin.cx X-Virus-Status: Clean X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 04 Mar 2017 19:43:38 -0000 On Saturday, March 04, 2017 10:52:46 AM Pedro Giffuni wrote: > > On 03/04/17 10:32, Slawa Olhovchenkov wrote: > > On Sat, Mar 04, 2017 at 03:04:17PM +0000, Pedro F. Giffuni wrote: > > > >> Author: pfg > >> Date: Sat Mar 4 15:04:17 2017 > >> New Revision: 314669 > >> URL: https://svnweb.freebsd.org/changeset/base/314669 > >> > >> Log: > >> Drop i486 from the default i386 GENERIC kernel configuration. > >> > >> 80486 production was stopped by Intel on September 2007. Dropping the 486 > >> configuration option from the GENERIC kernel improves performance > >> slightly. > >> > >> Removing I486_CPU is consistent at this time: we don't support any > >> processor without a FPU and the PC-98 arch, which frequently involved i486 > >> CPUs, is also gone so we don't test such platforms anymore. > > > > What is realy mean? > > This means we don't do work-arounds that would be required for raw 486. > Instead we will use the 586 instructions by default. This doesn't change that. The kernel already has runtime tests in place for new things on 486 and later via cpuid. > > Some Via CPU is like i486 (by instruction set). > > > > CPU: VIA Ezra (800.04-MHz 686-class CPU) > > Origin="CentaurHauls" Id=0x678 Family=0x6 Model=0x7 Stepping=8 > > Features=0x803035 > > AMD Features=0x80000000<3DNow!> > > > > 486 never had MMX extensions. > This is a 686, performance should improve ~4%. How did you measure the improvement? Keeping I486_CPU doesn't really do anything except remove a some #ifdef'd conditionals in identcpu.c and initcpu.c. It doesn't affect whether we use the TSC, MMX, etc. Those are all runtime checks based the CPU feature flags from cpuid. -- John Baldwin