Date: Thu, 27 Feb 2003 19:17:39 +0000 From: Nuno Teixeira <nunotex@aeiou.pt> To: freebsd-current@freebsd.org Subject: Re: -O2 considered harmful Message-ID: <20030227191739.GA607@gw.tex.bogus> In-Reply-To: <20030227025155.61529.qmail@web40310.mail.yahoo.com> References: <20030227025155.61529.qmail@web40310.mail.yahoo.com>
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On Wed, Feb 26, 2003 at 06:51:55PM -0800, Rhett Monteg Hollander wrote: > Nuno Teixeira wrote: > > > > Hi, > > > > Just a little question: > > > > Does -march=k6-2 implies -m3dnow? Or -march=pentiumpro implies -mmmx? > Pentium Pro doesn't support MMX; -march=pentiumpro (aka -march=i686) enables > compiling with main i686 instruction set, no MMX\SSE or whatever. > > > > > I always thought that when I use -march it will enable other > > porcessor specific optimizations like mmx and 3dnow (if available). > No way. Besides, only a dozen of open-source UNIX applications can really > profit from MMX, so it's absurd to use -mmmx for day-by-day use. To be correct, > MMX is only useful for real-time video\audio processing. > > A little example: consider some 16-bit pixel set that you need to increase > brightness, i.e. to add some value to every pixel. You can load a word into > integer register, process, and store. You can also load a quadword of four > 16-bit values into MMX register which is mapped onto FPU register, process them > at once, and store. Indeed to be faster. > > Enabling MMX usually results in about 50% performance increase for true CISC > processors like P-MMX, and about 20% for PII and up. > > --- > Regards, > Rhett > Hi, I understand it. Anyway, there is known problems by using -mmmx or -m3dnow on builworld/buildkernel? Well, I used allways march=pentiumpro on stable and now pentium2 on current without any problem. I use some applications like grip, lame, mplayer, etc. Maybe I get some extra performance running this apps. Thanks, Nuno Teixeira -- /* PGP fingerprint: C6D1 06ED EB54 A99C 6B14 6732 0A5D 810D 727D F6C6 */ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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