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Path: euryale.cc.adfa.oz.au!newshost.carno.net.au!harbinger.cc.monash.edu.au!munnari.OZ.AU!news.mel.connect.com.au!news.mira.net.au!news.vbc.net!garlic.com!news.scruz.net!kithrup.com!news.Stanford.EDU!newshub.internex.net!newshub1.internex.net!viper.inow.com!newsfeed1.aimnet.com!www.nntp.primenet.com!nntp.primenet.com!cs.utexas.edu!news.sprintlink.net!news-peer.sprintlink.net!news-peer.gsl.net!news.gsl.net!news.mathworks.com!newsfeed.internetmci.com!super.zippo.com!zdc!szdc!szdc-e!news From: "John S. Dyson" <dyson@indy.celebration.net> Newsgroups: comp.unix.bsd.freebsd.misc Subject: Re: gcc optimizations for kernel Date: Tue, 17 Sep 1996 11:20:46 -0700 Organization: AT&T Lines: 20 Message-ID: <323EEBFE.1689@indy.celebration.net> References: <51d0eg$9uf@usenet4.interramp.com> <323A693E.7B4C@OntheNet.com.au> <8791ad5jed.fsf@plm.xs4all.nl> <n0E175F6A@longacre.demon.co.uk> <87wwxv57zz.fsf@plm.xs4all.nl> Reply-To: dyson@indy.celebration.net Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Mailer: Mozilla 3.0 (WinNT; I) Peter Mutsaers wrote: > I never tried -O3. Then -O2 must be safe, but -O3 not. > > I would not use -O3 anyway since programs compiled with it tend to be > somewhat bigger than compiled with -O2 (loop-unroll > optimization?). For the kernel, occupying it's memory always, I'd > rather not have that. -O and -O2 make more difference than -O2 and -O3 > wrt speed, so I would suggest to use -O2. > I don't think that you really want to do anything (other than perhaps -fomit-frame-pointer) to make the kernel bigger. It busts the caches anyway (frustrating me greatly when I am trying to algorithmically improve the kernel, slowing things down, when they should be speeding up.) One of the biggest things that we could do to speed the kernel up (all else being equal) is to make it smaller... John