Date: Sun, 05 Mar 2017 15:24:59 -0800 From: John Baldwin <jhb@freebsd.org> To: Pedro Giffuni <pfg@freebsd.org> Cc: Slawa Olhovchenkov <slw@zxy.spb.ru>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r314669 - head/sys/i386/conf Message-ID: <1537596.qhqdTsTLLF@ralph.baldwin.cx> In-Reply-To: <c5fc59db-3d9a-92f9-0e10-e9002b38b9f8@FreeBSD.org> References: <201703041504.v24F4HMh023937@repo.freebsd.org> <7873439.f6BlOXHt6g@ralph.baldwin.cx> <c5fc59db-3d9a-92f9-0e10-e9002b38b9f8@FreeBSD.org>
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On Saturday, March 04, 2017 08:14:11 PM Pedro Giffuni wrote: > > On 3/4/2017 5:51 PM, John Baldwin wrote: > > On Saturday, March 04, 2017 03:49:52 PM Pedro Giffuni wrote: > >>> Il giorno 04 mar 2017, alle ore 14:43, John Baldwin <jhb@freebsd.org> ha scritto: > >>> > >>> 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. > >>> > >> Hmm ..then I am wondering if I effectively changed anything? > > The only change is a 486 now panics on boot when it used to work fine. :-/ > > > > Nothing for other CPUs has changed. > > Not much has been lost then. > FWIW, I have a "Pentium overdrive" somewhere in the basement which could > theoretically boot FreeBSD 12 but last I remember just rebuilding a > kernel was painful and the memory and HD limitations really make it a no-go. So I would rather support 486 in GENERIC or not support it at all. It doesn't cost anything for it to be in GENERIC, so if we have it, I think we should ship it. Also, the original justification for this commit of a 4% performance gain doesn't seem to have any basis in fact. The one gain I can think of is de-cluttering some things like identcpu.c and initcpu.c which can only happen if we remove code entirely, not from removing an option in GENERIC. -- John Baldwin
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