Re: [PATCH] pgo: add clang's Profile Guided Optimization infrastructure

Sedat Dilek
2021-01-21T04:59:12Z

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Hi,

When I looked through the code I wondered why we do not add a
"CONFIG_PGO_CLANG_PROFDATA" which can be helpful when doing the PGO
rebuild with a vmlinux.profdata.

This introduces a "PGO_PROFDATA" to turn on/off to pass
"-fprofile-use=vmlinux.profdata" (see CFLAGS_PGO_CLANG_PROFDATA in
top-level Makefile).

If we turn off via "PGO_PROFILE := n" in several Makefiles - we should
do the same and add "PGO_PROFDATA := n" to the same Makefiles?

Please see the attached diff.

Regards,
- Sedat -

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diff --git a/Makefile b/Makefile
index dd58fca65c9f..d9a48279c4d5 100644
--- a/Makefile
+++ b/Makefile
@@ -660,7 +660,8 @@ endif # KBUILD_EXTMOD
all: vmlinux

CFLAGS_PGO_CLANG := -fprofile-generate
-export CFLAGS_PGO_CLANG
+CFLAGS_PGO_CLANG_PROFDATA := -fprofile-use=vmlinux.profdata
+export CFLAGS_PGO_CLANG CFLAGS_PGO_CLANG_PROFDATA

CFLAGS_GCOV := -fprofile-arcs -ftest-coverage \
$(call cc-option,-fno-tree-loop-im) \
diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
index 383853e32f67..3268d1ee6e45 100644
--- a/arch/x86/boot/Makefile
+++ b/arch/x86/boot/Makefile
@@ -72,6 +72,7 @@ KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
GCOV_PROFILE := n
PGO_PROFILE := n
+PGO_PROFDATA := n
UBSAN_SANITIZE := n

$(obj)/bzImage: asflags-y := $(SVGA_MODE)
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index ed12ab65f606..707c4034aef7 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -55,6 +55,7 @@ CFLAGS_sev-es.o += -I$(objtree)/arch/x86/lib/
KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
GCOV_PROFILE := n
PGO_PROFILE := n
+PGO_PROFDATA := n
UBSAN_SANITIZE :=n

KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
diff --git a/arch/x86/crypto/Makefile b/arch/x86/crypto/Makefile
index baa14f83edae..1b2cb9142672 100644
--- a/arch/x86/crypto/Makefile
+++ b/arch/x86/crypto/Makefile
@@ -5,6 +5,7 @@
OBJECT_FILES_NON_STANDARD := y

PGO_PROFILE_curve25519-x86_64.o := n
+PGO_PROFDATA_curve25519-x86_64.o := n

obj-$(CONFIG_CRYPTO_TWOFISH_586) += twofish-i586.o
twofish-i586-y := twofish-i586-asm_32.o twofish_glue.o
diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
index f7421e44725a..67860ecde542 100644
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -181,6 +181,7 @@ VDSO_LDFLAGS = -shared --hash-style=both --build-id=sha1 \
$(call ld-option, --eh-frame-hdr) -Bsymbolic
GCOV_PROFILE := n
PGO_PROFILE := n
+PGO_PROFDATA := n

quiet_cmd_vdso_and_check = VDSO $@
cmd_vdso_and_check = $(cmd_vdso); $(cmd_vdso_check)
diff --git a/arch/x86/platform/efi/Makefile b/arch/x86/platform/efi/Makefile
index 5f22b31446ad..5d64b728a0a0 100644
--- a/arch/x86/platform/efi/Makefile
+++ b/arch/x86/platform/efi/Makefile
@@ -3,6 +3,7 @@ OBJECT_FILES_NON_STANDARD_efi_thunk_$(BITS).o := y
KASAN_SANITIZE := n
GCOV_PROFILE := n
PGO_PROFILE := n
+PGO_PROFDATA := n

obj-$(CONFIG_EFI) += quirks.o efi.o efi_$(BITS).o efi_stub_$(BITS).o
obj-$(CONFIG_EFI_MIXED) += efi_thunk_$(BITS).o
diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index 36f20e99da0b..99f2e4c1886e 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -24,6 +24,7 @@ targets += purgatory.ro purgatory.chk
# Sanitizer, etc. runtimes are unavailable and cannot be linked here.
GCOV_PROFILE := n
PGO_PROFILE := n
+PGO_PROFDATA := n
KASAN_SANITIZE := n
UBSAN_SANITIZE := n
KCSAN_SANITIZE := n
diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefile
index 21797192f958..a495890e9b11 100644
--- a/arch/x86/realmode/rm/Makefile
+++ b/arch/x86/realmode/rm/Makefile
@@ -77,4 +77,5 @@ KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
GCOV_PROFILE := n
PGO_PROFILE := n
+PGO_PROFDATA := n
UBSAN_SANITIZE := n
diff --git a/arch/x86/um/vdso/Makefile b/arch/x86/um/vdso/Makefile
index 54f5768f5853..2e9cdc137ade 100644
--- a/arch/x86/um/vdso/Makefile
+++ b/arch/x86/um/vdso/Makefile
@@ -65,6 +65,7 @@ quiet_cmd_vdso = VDSO $@
VDSO_LDFLAGS = -fPIC -shared -Wl,--hash-style=sysv
GCOV_PROFILE := n
PGO_PROFILE := n
+PGO_PROFDATA := n

#
# Install the unstripped copy of vdso*.so listed in $(vdso-install-y).
diff --git a/kernel/pgo/Kconfig b/kernel/pgo/Kconfig
index 5fe9635ac64c..ce1e1c061a98 100644
--- a/kernel/pgo/Kconfig
+++ b/kernel/pgo/Kconfig
@@ -32,4 +32,8 @@ config PGO_CLANG
Note that the debugfs filesystem has to be mounted to access
profiling data.

+config PGO_CLANG_PROFDATA
+ bool "Use vmlinux.profdata profile file"
+ depends on !PGO_CLANG
+
endmenu
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 12fed825ab4b..14169a575b64 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -154,6 +154,12 @@ _c_flags += $(if $(patsubst n%,, \
$(PGO_PROFILE_$(basetarget).o)$(PGO_PROFILE)y), \
$(CFLAGS_PGO_CLANG))
endif
+# Use vmlinux.profdata profile file
+ifeq ($(CONFIG_PGO_CLANG_PROFDATA),y)
+_c_flags += $(if $(patsubst n%,, \
+ $(PGO_PROFDATA_$(basetarget).o)$(PGO_PROFDATA)y), \
+ $(CFLAGS_PGO_CLANG_PROFDATA))
+endif

#
# Enable address sanitizer flags for kernel except some files or directories