Date: Tue, 25 Jul 2000 16:38:01 -0500 From: "Jeffrey J. Mountin" <jeff-ml@mountin.net> To: Otter <otterr@telocity.com>, Dave Boers <djb@ifa.au.dk> Cc: stable@FreeBSD.ORG Subject: Re: Recommended compilation optimizations Message-ID: <4.3.2.20000725153431.00d66d60@207.227.119.2> In-Reply-To: <Pine.BSF.4.21.0007241853130.329-100000@kashmir.telocity.co m> References: <20000724152021.A61713@relativity.student.utwente.nl>
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At 06:54 PM 7/24/00 +0000, Otter wrote: >what about the -march=pentiumpro flag? there's a bunch more >possibilities listed if you man gcc. keep in mind that the more opts you >add in, the longer it will take to compile something. And -march=pentiumpro differs from -march=i686 in what way? No sarcasm, just pointing this out since both have been mentioned. Using -march implies -mcpu, so '-march=X -mcpu=X' is the same as '-march=X'. Dropping the -mcpu means less clutter on the screen. Just as using i?86 does. When combined with anything above -O (-O2) will tend to blow up, either all the time or more often. From what I have seen/read this is not the case with just -mcpu=X. Throwing flags for fun isn't advised and in most cases the improvements are minimal. After reading the man pages, etc, some make sense to have (ie -march and -cpu). However, don't recall ever seeing any performance data. OTOH, there can be significant changes. Then one must decide if the program is used enough to justify the risk. Talking system here, not ports, which do their own thing in most cases, unless you have CFLAGS set. Most ports will take a -O2, but then you need to change it back before doing the world. Frankly I got tired of switching (and forgetting to) and just stick with '-O -pipe' and hack the ports as needed/desired. As mentioned it is also faster building world. AFAICR, about 15% faster using '-O -pipe' than '-O2 -pipe'. .02 Jeff Mountin - jeff@mountin.net Systems/Network Administrator FreeBSD - the power to serve To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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