Date: Tue, 14 Jan 1997 22:20:47 +0100 From: Magnus Enbom <dot@cdt.luth.se> To: Joao Carlos Mendes Luis <jonny@mailhost.coppe.ufrj.br> Cc: andrew@ugh.net.au, hackers@freebsd.org, dot@cdt.luth.se Subject: Re: Compiling kernel with optimisation Message-ID: <199701142120.WAA14508@garlic.cdt.luth.se> In-Reply-To: Your message of "Sun, 12 Jan 1997 20:31:17 -0200." <199701122231.UAA22599@gaia.coppe.ufrj.br>
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> #define quoting(David Greenman) > // >I just noticed that when compiling a kernel it is done with the -O flag. > // >Would there be much speed improvement in the sytem if it was done with > // >-O3? Would this break the kernel or is the added time it takes to compile > // >not worth the benfits? > // > // It has very little effect on performance and optimizations levels > "-O" > // have traditionally been broken in gcc. > > Well, the NetBSD team has managed to compile their kernel with -O6 > and -Wall, but they had to change lots of things.. > > I don't know what do you call "little effect on performance", but > 5% gain would be enough to make me think about. Unfortunately, > I don't have any measurements (and even don't know how to do them). > > I tried -O6 once, and 2 files were broken in compile time !!! (Wow) > I did dare once more, fixing those files and running that kernel. > Panic in 5 seconds. :( I've built kernels with -O2 -m486 and used them without problems. If you're using anything higher you get the -finline-functions option added to gcc, that will break a few things. /.
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