Enable the machine function split optimization for AutoFDO in Clang. Machine function split (MFS) is a pass in the Clang compiler that splits a function into hot and cold parts. The linker groups all cold blocks across functions together. This decreases hot code fragmentation and improves iCache and iTLB utilization. MFS requires a profile so this is enabled only for the AutoFDO builds. Co-developed-by: Han Shen <shenhan@xxxxxxxxxx> Signed-off-by: Han Shen <shenhan@xxxxxxxxxx> Signed-off-by: Rong Xu <xur@xxxxxxxxxx> Suggested-by: Sriraman Tallam <tmsriram@xxxxxxxxxx> Suggested-by: Krzysztof Pszeniczny <kpszeniczny@xxxxxxxxxx> --- include/asm-generic/vmlinux.lds.h | 6 ++++++ scripts/Makefile.autofdo | 2 ++ 2 files changed, 8 insertions(+) diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index ace617d1af9b..20e46c0917db 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -565,9 +565,14 @@ defined(CONFIG_AUTOFDO_CLANG) __unlikely_text_start = .; \ *(.text.unlikely .text.unlikely.*) \ __unlikely_text_end = .; +#define TEXT_SPLIT \ + __split_text_start = .; \ + *(.text.split .text.split.[0-9a-zA-Z_]*) \ + __split_text_end = .; #else #define TEXT_HOT *(.text.hot .text.hot.*) #define TEXT_UNLIKELY *(.text.unlikely .text.unlikely.*) +#define TEXT_SPLIT #endif /* @@ -584,6 +589,7 @@ defined(CONFIG_AUTOFDO_CLANG) ALIGN_FUNCTION(); \ *(.text.asan.* .text.tsan.*) \ *(.text.unknown .text.unknown.*) \ + TEXT_SPLIT \ TEXT_UNLIKELY \ . = ALIGN(PAGE_SIZE); \ TEXT_HOT \ diff --git a/scripts/Makefile.autofdo b/scripts/Makefile.autofdo index 9c9a530ef090..380042a301cc 100644 --- a/scripts/Makefile.autofdo +++ b/scripts/Makefile.autofdo @@ -11,6 +11,7 @@ endif ifdef CLANG_AUTOFDO_PROFILE CFLAGS_AUTOFDO_CLANG += -fprofile-sample-use=$(CLANG_AUTOFDO_PROFILE) -ffunction-sections + CFLAGS_AUTOFDO_CLANG += -fsplit-machine-functions endif ifdef CONFIG_LTO_CLANG_THIN @@ -18,6 +19,7 @@ ifdef CONFIG_LTO_CLANG_THIN KBUILD_LDFLAGS += --lto-sample-profile=$(CLANG_AUTOFDO_PROFILE) endif KBUILD_LDFLAGS += --mllvm=-enable-fs-discriminator=true --mllvm=-improved-fs-discriminator=true -plugin-opt=thinlto + KBUILD_LDFLAGS += -plugin-opt=-split-machine-functions endif export CFLAGS_AUTOFDO_CLANG -- 2.47.0.rc1.288.g06298d1525-goog