Date: Sat, 8 Apr 2000 18:05:55 -0400 (EDT) From: Kenneth Wayne Culver <culverk@wam.umd.edu> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: Kris Kennaway <kris@FreeBSD.ORG>, "Alexey N. Dokuchaev" <danfe@inet.ssc.nsu.ru>, freebsd-hackers@FreeBSD.ORG Subject: Re: What are the best gcc optimization options for Pentium 200 MMX Message-ID: <Pine.GSO.4.21.0004081804090.10178-100000@rac3.wam.umd.edu> In-Reply-To: <200004082134.OAA12743@apollo.backplane.com>
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Why exactly whould you not touch the -march options? I have had no problems using them, and my system (5.0-CURRENT) seems a little faster with -march=i686. I could be wrong though as I havn't done any exact tests... it just seems a bit more responsive.. ================================================================= | Kenneth Culver | FreeBSD: The best OS around. | | Unix Systems Administrator | ICQ #: 24767726 | | and student at The | AIM: muythaibxr | | The University of Maryland, | Website: (Under Construction) | | College Park. | http://www.wam.umd.edu/~culverk/| ================================================================= On Sat, 8 Apr 2000, Matthew Dillon wrote: > :On Sat, 8 Apr 2000, Alexey N. Dokuchaev wrote: > : > :> AFAIK, Linux Mandrake has it's kernel and userland highly optimized for > :> Pentium architecture. However, they have additional gcc optimization > :> flags turned on by default, including -O3 and -mfast_math. > : > :Can you say "gimmick"? :-) gcc often produces demonstrably broken code for > :optimisation levels higher than -O. > : > :Probably the only useful and safe option apart from -O is the > :-march=pentium/pentiumpro/pentiumii/etc option for using > :processor-specific opcodes and instruction scheduling. > :Kris > > I use -Os for everything. I wouldn't bother with anything else. Someone > ran a bunch of benchmarks with various gcc/egcs options a while back > and, frankly, the top half dozen combinations were so close to each > other performance-wise that it just didn't matter. -Os was in that > group, but also produced significantly smaller binaries. > > I wouldn't touch the -march stuff at all, nor would I use -O3 (which > tries to inline standard static functions verses -O2) - that's useless > on IA32 because call/returns are very fast (I had an argument with John > Dyson about call/return overhead verses an L1 cache miss and > we ran a bunch of timings. I lost the argument :-) call/return won the > race handily). > > > -Matt > Matthew Dillon > <dillon@backplane.com> > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-hackers" in the body of the message > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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