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<FPU,DE,TSC,MSR,MTRR,PGE,MMX> > > 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 _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
