Date: Sun, 5 Mar 2017 21:43:03 -0500 From: Pedro Giffuni <pfg@FreeBSD.org> To: John Baldwin <jhb@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: <3351E9C7-CC12-472A-9E81-4973710E9C8C@FreeBSD.org> In-Reply-To: <1537596.qhqdTsTLLF@ralph.baldwin.cx> References: <201703041504.v24F4HMh023937@repo.freebsd.org> <7873439.f6BlOXHt6g@ralph.baldwin.cx> <c5fc59db-3d9a-92f9-0e10-e9002b38b9f8@FreeBSD.org> <1537596.qhqdTsTLLF@ralph.baldwin.cx>
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> Il giorno 05 mar 2017, alle ore 18:24, John Baldwin <jhb@freebsd.org> = ha scritto: >=20 > On Saturday, March 04, 2017 08:14:11 PM Pedro Giffuni wrote: >>=20 >> 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: >>>>>=20 >>>>> 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: >>>>>>>=20 >>>>>>>> Author: pfg >>>>>>>> Date: Sat Mar 4 15:04:17 2017 >>>>>>>> New Revision: 314669 >>>>>>>> URL: https://svnweb.freebsd.org/changeset/base/314669 >>>>>>>>=20 >>>>>>>> Log: >>>>>>>> Drop i486 from the default i386 GENERIC kernel configuration. >>>>>>>>=20 >>>>>>>> 80486 production was stopped by Intel on September 2007. = Dropping the 486 >>>>>>>> configuration option from the GENERIC kernel improves = performance >>>>>>>> slightly. >>>>>>>>=20 >>>>>>>> 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. >>>>>=20 >>>> 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. :-/ >>>=20 >>> Nothing for other CPUs has changed. >>=20 >> Not much has been lost then. >> FWIW, I have a "Pentium overdrive" somewhere in the basement which = could=20 >> theoretically boot FreeBSD 12 but last I remember just rebuilding a=20= >> kernel was painful and the memory and HD limitations really make it a = no-go. >=20 > 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. >=20 OK, that=E2=80=99s reasonable. I will revert the change. Pedro.
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