On Tue, 23 Oct 2001, Christine Ames wrote: > Snipped from "man gcc": <snip> I can't imagine anyone attempting kernel programming (including me) without knowing about the optimisation flags. My question was why this level is *needed* for modules, and not, say, -O3. On Tue, 23 Oct 2001, Erik Mouw wrote: > The most important is the compiler uses -finline in this particular > case, so it does indeed pay attention to the 'inline' keyword. Without > that, it won't and that's exactly the reason why modules compiled > without -O2 fail to link or load. Now this answers the question, thanks. However, it makes me wonder if optimisations like -O3 wouldn't also work? Also, if I made a monolithic kernel would the lack of the -finline flag matter? Resolving symbols might fail for modprobe if I were building modules, but the static linker should be fine shouldn't it? (this is a purely academic question as I always use modules) > > -O3 > > Optimize yet more. This turns on everything -O2 does, along with also > > turning on -finline-func*- tions. > > And it also enables -funroll-all-loops which isn't too smart. In most > of the cases -O3 actually generates *slower* code than -O2 because > unrolling all loops makes the code larger so it won't fit in the > I-cache anymore. To give you an idea how expensive a cache miss is: on > StrongARM CPU a single cache miss costs you about 60 cycles. This shows that -O3 will be slower, but will it still work? TIA, Paul Gearon Software Engineer Telephone: +61 7 3876 2188 Plugged In Software Fax: +61 7 3876 4899 http://www.PIsoftware.com PGP Key available via finger Catapultam habeo. Nisi pecuniam omnem mihi dabis, ad caput tuum saxum immane mittam. (Translation from latin: "I have a catapult. Give me all the money, or I will fling an enormous rock at your head.") - Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ IRC Channel: irc.openprojects.net / #kernelnewbies Web Page: http://www.kernelnewbies.org/
