Date: Sat, 4 Mar 2017 15:49:52 -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: <D81029FA-61CF-4648-A2A8-8570DEF28B14@FreeBSD.org> In-Reply-To: <2368011.hGEX4V32U5@ralph.baldwin.cx> References: <201703041504.v24F4HMh023937@repo.freebsd.org> <20170304153228.GM15630@zxy.spb.ru> <ef83ffe1-6198-3468-d132-849c5d38f52d@apache.org> <2368011.hGEX4V32U5@ralph.baldwin.cx>
next in thread | previous in thread | raw e-mail | index | archive | help
> 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: >>=20 >> 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. >>>=20 >>> What is realy mean? >>=20 >> This means we don't do work-arounds that would be required for raw = 486. >> Instead we will use the 586 instructions by default. >=20 > 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? >>> Some Via CPU is like i486 (by instruction set). >>>=20 >>> CPU: VIA Ezra (800.04-MHz 686-class CPU) >>> Origin=3D"CentaurHauls" Id=3D0x678 Family=3D0x6 Model=3D0x7 = Stepping=3D8 >>> Features=3D0x803035<FPU,DE,TSC,MSR,MTRR,PGE,MMX> >>> AMD Features=3D0x80000000<3DNow!> >>>=20 >>=20 >> 486 never had MMX extensions. >> This is a 686, performance should improve ~4%. >=20 > 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. >=20 The number came out from an old posting involving buildworld times, = which I can=E2=80=99t find now :(. Things seem to have changed a lot: it was surely using GCC back then, I = don=E2=80=99t believe clang does much distinction about 486 at all. BTW, does it make sense to keep i586 in the configuration still? Both = i486 and i586 were once removed but later re-instated in r205336. Pedro.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?D81029FA-61CF-4648-A2A8-8570DEF28B14>