Date: Thu, 15 Dec 2005 06:43:20 -0600 From: Randy Rowe <rerowe@rerowe.com> To: noackjr@alumni.rice.edu Cc: stable@freebsd.org Subject: Re: kernel cpu entries Message-ID: <43A164E8.7040700@rerowe.com> In-Reply-To: <43A0E607.2030101@alumni.rice.edu> References: <20051215002618.B4D3B5D07@ptavv.es.net> <43A0E607.2030101@alumni.rice.edu>
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Jonathan Noack wrote: > Kevin Oberman wrote: > >> Scott Long wrote: >> >>> Also, taking out CPU_I586 is usually a bad idea. It offers no >>> performance penalties (unlike CPU_I386 and maybe CPU_I486), but >>> enables things like optimized bcopy. >> >> >> Ahh, This is the sort of thing I never realized. Is there anything in >> the handbook that covers this? I had always been under the impression >> that CPU_I686 enabled all things that the 686 was capable of. I will >> build a new kernel to add that back in. > > > From tuning(7): > ************************************************** > There are a number of *_CPU options that can be commented out. If you > only want the kernel to run on a Pentium class CPU, you can easily > remove I486_CPU, but only remove I586_CPU if you are sure your CPU is > being recognized as a Pentium II or better. Some clones may be > recognized as a Pentium or even a 486 and not be able to boot without > those options. If it works, great! The operating system will be able > to better use higher-end CPU features for MMU, task switching, > timebase, and even device operations... > ************************************************** > > From /sys/i386/conf/NOTES: > ************************************************** > # You must specify at least one CPU (the one you intend to run on); > # deleting the specification for CPUs you don't need to use may make > # parts of the system run faster. > ************************************************** > > From npx(4) (also see /sys/i386/i386/support.s): > ************************************************** > The NPX registers are normally used to optimize copying and zeroing > when all of the following conditions are satisfied: > 1. cpu I586_CPU is an option > ... > Then copying and zeroing using the NPX registers is normally 30-100% > faster. > ************************************************** > > All is rosy until you see that I586_CPU looks like a loss for blowfish > (if you have an i686 CPU): > /sys/crypto/blowfish/arch/i386/bf_enc.S > > As I use AES, I guess I586_CPU is a win for me. Despite this, I think > it makes the most sense for I686_CPU to enable the optimized bcopy if > it really is a win for i686 CPUs. > > -Jonathan > _______________________________________________ > freebsd-stable@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-stable > To unsubscribe, send any mail to "freebsd-stable-unsubscribe@freebsd.org" As another entry point here, this is from LINT on 4.x ##################################################################### # CPU OPTIONS # # You must specify at least one CPU (the one you intend to run on); # deleting the specification for CPUs you don't need to use may make # parts of the system run faster. This is especially true removing # I386_CPU. # cpu I386_CPU cpu I486_CPU cpu I586_CPU # aka Pentium(tm) cpu I686_CPU # aka Pentium Pro(tm) I have multiple dual and quad Pentium Pro machines running 4.x that have been remarkably stable using the I686_CPU setting (kudos to the developers!!). So I add myself to the list of those that have been removing the I586_CPU option. Randy
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