Date: Sat, 18 Mar 2000 16:02:52 -0500 From: Donn Miller <dmmiller@cvzoom.net> To: obrien@FreeBSD.ORG Cc: Thomas =?iso-8859-1?Q?K=F6llmann?= <koellmann@gmx.net>, R Joseph Wright <rjoseph@nwlink.com>, freebsd-current@FreeBSD.ORG Subject: Re: gcc -Os optimisation broken (RELENG_4) Message-ID: <38D3EEFC.FD0E5C5D@cvzoom.net> References: <20000317125045.A15480@schumann.cx> <Pine.BSF.4.21.0003170922440.9372-100000@mammalia.sea> <20000318031845.A1816@home.net> <20000318110022.A60879@dragon.nuxi.com>
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David O'Brien wrote: > > On Sat, Mar 18, 2000 at 03:18:45AM +0100, Thomas Köllmann wrote: > > If it doesn't I'll probably try `-03 -pipe -march=pentium' come next > > What are people hoping to get by doing this? Are you actually doing a > scientific performance evaluation between the various optimization > options??? Are are people just being macho, and thinking they are > getting all this non-existent performance increase? It's probably more of a "placebo effect", which makes you think your are getting a big boost in performance. I'll admit that I've never seen a whole order or magnitude increase in performance between -O and -mpentium-O3, or whatever - it probably gives you boosts here and there. Optimization is pretty good, as I've found out, with plain-jane -O. Beyond that, I think your performance gains are minimal. And yes, I think it's really macho to be usin' hopped-up CFLAGS, like -march=pentium -Os -pipe. I feel really studly doing this. :-) We should do a survey, and find out what the guys use for CFLAGS and COPTFLAGS and compare them to what the female users are using. That would be interesting. I don't know, -O seems to be doing some pretty decent optimization, from what I've seen of the assembler output. I guess you're right in that all higher optimization are prividing marginal performance gains. From what I gather, the i386 arch. is not very sensitive to optimization from gcc. You'll see minor boosts here and there, but that's about it. Typically, guys that are diehard football fans like to use -mpentium -O3 -pipe for building world and kernel. - Donn To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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