Messages in this thread Patch in this message | | | Date | Sun, 27 Apr 2008 20:31:31 +0200 | From | Sam Ravnborg <> | Subject | Re: [PATCH] prepare kconfig inline optimization for all architectures |
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On Sun, Apr 27, 2008 at 02:14:12PM -0400, Christoph Hellwig wrote: > On Sun, Apr 27, 2008 at 08:09:57PM +0200, Sam Ravnborg wrote: > > With the config option we pass the inline hint to gcc (if enabled). > > So with the config option we have the possibility to pass a _hint_ to > > gcc about inlining. > > > > Before the config option there were no difference between > > static int alwyas_inline foo() {} > > and > > static int inline foo() {} > > > > With the config option we now have a situation where they actually > > differ as they should do (assuming gcc > 4.x). > > As Linus mentioned the hint doesn't make any sense because gcc will > get it wrong anyway. In fact when you look at kernel code it tends > to inline the everything and the kitchensink as long as there's just > one caller and this bloat the stack but doesn't inline where it needs > to. Better don't try to mess with that and do it explicit.
The tendency is that gcc inline *more than we whish* - not less. Which is why we have noinline - to cover the cases where we do not want stuff inlined.
What the patch in question does is to make a difference between always_inle and inline. Previously they were the same. With the patch applied and with a gcc > 4.0 inline is now a hint.
Did you actually read the patch?
> > > So you say that it is safe to assume all places where we really need > > always_inline are annotedted such - and we do not need a simple > > config option that the user can uncheck. > > I don't say it is that, it certainly isn't on powerpc and probably most > other architectures right now, because only x86 got the fixup so far. > But making it a user-visible option instead of an architecture opt > in/out selection doesn't make any sense. If you read the patch you will see that the architectures that want to enable this has to do an explicit HAVE_CC_INLINE_HINT so powerpc is not impacted by this until they request it. Exactly the reason why this was not widely enabled in the first place (but implemnted in a too x86 specific way).
Updated patch below. I btw. renamed the option to say this is about a INLINE_HINT.
Sam
diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig index 49590f8..9645a6f 100644 --- a/arch/sparc/Kconfig +++ b/arch/sparc/Kconfig @@ -68,6 +68,7 @@ config SPARC default y select HAVE_IDE select HAVE_OPROFILE + select HAVE_CC_INLINE_HINT # Identify this as a Sparc32 build config SPARC32 diff --git a/arch/sparc64/Kconfig b/arch/sparc64/Kconfig index 8acc5cc..3c8ba36 100644 --- a/arch/sparc64/Kconfig +++ b/arch/sparc64/Kconfig @@ -9,6 +9,7 @@ config SPARC bool default y select HAVE_OPROFILE + select HAVE_CC_INLINE_HINT select HAVE_KPROBES select HAVE_KRETPROBES diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 2fadf79..48e352b 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -20,6 +20,7 @@ config X86 def_bool y select HAVE_IDE select HAVE_OPROFILE + select HAVE_CC_INLINE_HINT select HAVE_KPROBES select HAVE_KRETPROBES select HAVE_KVM if ((X86_32 && !X86_VOYAGER && !X86_VISWS && !X86_NUMAQ) || X86_64) @@ -142,9 +143,6 @@ config AUDIT_ARCH config ARCH_SUPPORTS_AOUT def_bool y -config ARCH_SUPPORTS_OPTIMIZED_INLINING - def_bool y - # Use the generic interrupt handling code in kernel/irq/: config GENERIC_HARDIRQS bool diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug index 5b1979a..23956ea 100644 --- a/arch/x86/Kconfig.debug +++ b/arch/x86/Kconfig.debug @@ -258,15 +258,3 @@ config CPA_DEBUG endmenu -config OPTIMIZE_INLINING - bool "Allow gcc to uninline functions marked 'inline'" - default y - help - This option determines if the kernel forces gcc to inline the functions - developers have marked 'inline'. Doing so takes away freedom from gcc to - do what it thinks is best, which is desirable for the gcc 3.x series of - compilers. The gcc 4.x series have a rewritten inlining algorithm and - disabling this option will generate a smaller kernel there. Hopefully - this algorithm is so good that allowing gcc4 to make the decision can - become the default in the future, until then this option is there to - test gcc for this. diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index b2fd754..e49fade 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -31,8 +31,7 @@ /* * Force always-inline if the user requests it so via the .config: */ -#if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) || \ - !defined(CONFIG_OPTIMIZE_INLINING) && (__GNUC__ >= 4) +#if !(defined(CONFIG_HAVE_CC_INLINE_HINT) && (__GNUC__ >= 4)) # define inline inline __attribute__((always_inline)) # define __inline__ __inline__ __attribute__((always_inline)) # define __inline __inline __attribute__((always_inline)) diff --git a/init/Kconfig b/init/Kconfig index ba3a389..3568647 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -508,6 +508,13 @@ config CC_OPTIMIZE_FOR_SIZE If unsure, say N. +# archs shall "select HAVE_CC_INLINE_HINT" +# to avoid forcing all function annotated inline +# to be inline. +# Note: This is only enforced for gcc > 4.0 +config HAVE_CC_INLINE_HINT + def_bool n + config SYSCTL bool
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