On Tue, Sep 10, 2019 at 9:46 AM Will Deacon <[email protected]> wrote: > > On Mon, Sep 09, 2019 at 10:21:35PM +0200, Arnd Bergmann wrote: > > On arm64 build with clang, sometimes the __cmpxchg_mb is not inlined > > when CONFIG_OPTIMIZE_INLINING is set. > > Hmm. Given that CONFIG_OPTIMIZE_INLINING has also been shown to break > assignment of local 'register' variables on GCC, perhaps we should just > disable that option for arm64 (at least) since we don't have any toolchains > that seem to like it very much! I'd certainly prefer that over playing > whack-a-mole with __always_inline.
Right, but I can also see good reasons to keep going: - In theory, CONFIG_OPTIMIZE_INLINING is the right thing to do -- the compilers also make some particularly bad decisions around inlining when each inline turns into an __always_inline, as has been the case in Linux for a long time. I think in most cases, we get better object code with CONFIG_OPTIMIZE_INLINING and in the cases where this is worse, it may be better to fix the compiler. The new "asm_inline" macro should also help with that. - The x86 folks have apparently whacked most of the moles already, see this commit from 2008 commit 3f9b5cc018566ad9562df0648395649aebdbc5e0 Author: Ingo Molnar <[email protected]> Date: Fri Jul 18 16:30:05 2008 +0200 x86: re-enable OPTIMIZE_INLINING re-enable OPTIMIZE_INLINING more widely. Jeff Dike fixed the remaining outstanding issue in this commit: | commit 4f81c5350b44bcc501ab6f8a089b16d064b4d2f6 | Author: Jeff Dike <[email protected]> | Date: Mon Jul 7 13:36:56 2008 -0400 | | [UML] fix gcc ICEs and unresolved externs [...] | This patch reintroduces unit-at-a-time for gcc >= 4.0, bringing back the | possibility of Uli's crash. If that happens, we'll debug it. it's still default-off and thus opt-in. - The inlining decisions of gcc and clang are already very different, and the bugs we are finding around that are much more common than the difference between CONFIG_OPTIMIZE_INLINING=y/n on a given compiler. Arnd
