mingo at elte
Apr 26, 2008, 9:11 AM
Post #1 of 1
(1154 views)
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[git pull] x86, generic: optimized inlining
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Linus, please pull the "optimized inlining" feature from:
git://git.kernel.org/pub/scm/linux/kernel/git/x86/linux-2.6-x86-optimized-inlining.git for-linus
this is from x86.git but touches include/linux/compiler-gcc.h and can be
enabled by other architectures as well. The motivation of this feature
is a 2.3% kernel text size reduction on generic x86 distro kernel
configs. (Perhaps gcc will also get smarter about inlining decisions if
the kernel gives it leeway about it.)
This change makes __always_inline more meaningful (and more critical).
Testing so far showed no ill effects.
Thanks,
Ingo
------------------>
Ingo Molnar (2):
x86: add optimized inlining
generic: make optimized inlining arch-opt-in
arch/x86/Kconfig | 3 +++
arch/x86/Kconfig.debug | 13 +++++++++++++
arch/x86/configs/i386_defconfig | 1 +
arch/x86/configs/x86_64_defconfig | 1 +
include/linux/compiler-gcc.h | 13 ++++++++++---
5 files changed, 28 insertions(+), 3 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 4d350b5..3b6ff3b 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -142,6 +142,9 @@ 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 239fd9f..5b1979a 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -257,3 +257,16 @@ config CPA_DEBUG
Do change_page_attr() self-tests every 30 seconds.
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/arch/x86/configs/i386_defconfig b/arch/x86/configs/i386_defconfig
index 3df340b..ad7ddaa 100644
--- a/arch/x86/configs/i386_defconfig
+++ b/arch/x86/configs/i386_defconfig
@@ -1421,6 +1421,7 @@ CONFIG_DEBUG_BUGVERBOSE=y
# CONFIG_DEBUG_VM is not set
# CONFIG_DEBUG_LIST is not set
# CONFIG_FRAME_POINTER is not set
+CONFIG_OPTIMIZE_INLINING=y
# CONFIG_RCU_TORTURE_TEST is not set
# CONFIG_LKDTM is not set
# CONFIG_FAULT_INJECTION is not set
diff --git a/arch/x86/configs/x86_64_defconfig b/arch/x86/configs/x86_64_defconfig
index eef98cb..2d6f5b2 100644
--- a/arch/x86/configs/x86_64_defconfig
+++ b/arch/x86/configs/x86_64_defconfig
@@ -1346,6 +1346,7 @@ CONFIG_DEBUG_BUGVERBOSE=y
# CONFIG_DEBUG_VM is not set
# CONFIG_DEBUG_LIST is not set
# CONFIG_FRAME_POINTER is not set
+CONFIG_OPTIMIZE_INLINING=y
# CONFIG_RCU_TORTURE_TEST is not set
# CONFIG_LKDTM is not set
# CONFIG_FAULT_INJECTION is not set
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index fe23792..b2fd754 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -28,9 +28,16 @@
#define __must_be_array(a) \
BUILD_BUG_ON_ZERO(__builtin_types_compatible_p(typeof(a), typeof(&a[0])))
-#define inline inline __attribute__((always_inline))
-#define __inline__ __inline__ __attribute__((always_inline))
-#define __inline __inline __attribute__((always_inline))
+/*
+ * 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)
+# define inline inline __attribute__((always_inline))
+# define __inline__ __inline__ __attribute__((always_inline))
+# define __inline __inline __attribute__((always_inline))
+#endif
+
#define __deprecated __attribute__((deprecated))
#define __packed __attribute__((packed))
#define __weak __attribute__((weak))
--
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