Public bug reported: There are a couple recent threads on lkml where the conclusion seems to be that CONFIG_OPTIMIZE_INLINING is not ready for use yet, and probably won't be until gcc 4.4 or 4.5. And that it was a mistake for it to be on in the defconfig, which is probably why it's on in Ubuntu's kernels: in Jaunty's kernel git tree: grep CONFIG_OPTIMIZE_INLINING debian/config/*/* debian/config/amd64/config:CONFIG_OPTIMIZE_INLINING=y debian/config/i386/config:CONFIG_OPTIMIZE_INLINING=y
It's in the "kernel hacking" section, right at the very end of the menu, if you use menuconfig or xconfig, BTW. The threads: http://lkml.org/lkml/2008/11/14/203 http://lkml.org/lkml/2009/1/4/289 CONFIG_OPTIMIZE_INLINING removes the workaround of defining inline as a macro for "inline __attribute__((always_inline))". (include/linux /compiler-gcc.h) This doesn't work well yet, because gcc will decide not to inline some functions that only generate decent code when inlined. e.g. constant_test_bit is only used if the bit number arguments is __builtin_constant_p(), so it will hopefully compile to an x86 "test" instruction, not a bunch of shifts and sometimes even an idiv. Anyway, a horrible 18 amd64 instructions long function. The other case of test_bit uses variable_test_bit, which uses inline asm (on x86) "bt; sbb". To see how many non-inlined copies of static inline int constant_test_bit() a kernel image has: do grep -c constant_test_bit /boot/System.map-2.6.27-11-generic 62 Jaunty: 88 /mnt/ubuntu-testing/boot/System.map-2.6.28-6-generic My custom-configured Jaunty kernel: 113 /boot/System.map-2.6.28-7-tesla (maybe some of the config options I turned off make more things compile-time constants) ** Affects: linux (Ubuntu) Importance: Undecided Status: New -- default config includes CONFIG_OPTIMIZE_INLINING=y https://bugs.launchpad.net/bugs/327788 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
