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 <shen...@google.com>
Signed-off-by: Han Shen <shen...@google.com>
Signed-off-by: Rong Xu <x...@google.com>
Suggested-by: Sriraman Tallam <tmsri...@google.com>
Suggested-by: Krzysztof Pszeniczny <kpszenic...@google.com>
---
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
