Date:	Mon, 27 Jun 2016 20:28:27 +0200
From:	Rabin Vincent <rabin@....in>
To:	mmarek@...e.com
Cc:	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	Rabin Vincent <rabin@....in>
Subject: [PATCH 2/2] kbuild: add shell cache

Running make results in over 40 invocations of the compiler just during
processing of the Makefile, before any actual rules are run.

To reduce this overhead, cache the results of $(shell) calls to the
compiler.

On my machine, this reduces make's processing time by over 96%:

$ make kernelversion && perf stat -r5 make kernelversion
Before: 0,252219929 seconds time elapsed ( +-  0,39% )
 After: 0,008607464 seconds time elapsed ( +-  0,50% )

Signed-off-by: Rabin Vincent <rabin@....in>
---
 Makefile               | 15 ++++++++-------
 scripts/Kbuild.include | 42 +++++++++++++++++++++++++++++++++++-------
 2 files changed, 43 insertions(+), 14 deletions(-)

diff --git a/Makefile b/Makefile
index 91baa282f3fa..90237e706bf8 100644
--- a/Makefile
+++ b/Makefile
@@ -304,11 +304,6 @@ HOSTCXX      = g++
 HOSTCFLAGS   = -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu89
 HOSTCXXFLAGS = -O2
 
-ifeq ($(shell $(HOSTCC) -v 2>&1 | grep -c "clang version"), 1)
-HOSTCFLAGS  += -Wno-unused-value -Wno-unused-parameter \
-		-Wno-missing-field-initializers -fno-delete-null-pointer-checks
-endif
-
 # Decide whether to build built-in, modular, or both.
 # Normally, just do built-in.
 
@@ -343,6 +338,11 @@ export KBUILD_CHECKSRC KBUILD_SRC KBUILD_EXTMOD
 scripts/Kbuild.include: ;
 include scripts/Kbuild.include
 
+ifeq ($(call cached-shell,$(HOSTCC) -v 2>&1 | grep -c "clang version"), 1)
+HOSTCFLAGS  += -Wno-unused-value -Wno-unused-parameter \
+		-Wno-missing-field-initializers -fno-delete-null-pointer-checks
+endif
+
 # Make variables (CC, etc...)
 AS		= $(CROSS_COMPILE)as
 LD		= $(CROSS_COMPILE)ld
@@ -767,7 +767,7 @@ KBUILD_CFLAGS += $(call cc-option, -fno-inline-functions-called-once)
 endif
 
 # arch Makefile may override CC so keep this after arch Makefile is included
-NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)
+NOSTDINC_FLAGS += -nostdinc -isystem $(call cached-shell,$(CC) -print-file-name=include)
 CHECKFLAGS     += $(NOSTDINC_FLAGS)
 
 # warn about C99 declaration after statement
@@ -798,7 +798,7 @@ KBUILD_CFLAGS   += $(call cc-option,-Werror=incompatible-pointer-types)
 KBUILD_ARFLAGS := $(call ar-option,D)
 
 # check for 'asm goto'
-ifeq ($(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-goto.sh $(CC)), y)
+ifeq ($(call cached-shell,$(CONFIG_SHELL) $(srctree)/scripts/gcc-goto.sh $(CC)), y)
 	KBUILD_CFLAGS += -DCC_HAVE_ASM_GOTO
 	KBUILD_AFLAGS += -DCC_HAVE_ASM_GOTO
 endif
@@ -1237,6 +1237,7 @@ endif # CONFIG_MODULES
 
 # Directories & files removed with 'make clean'
 CLEAN_DIRS  += $(MODVERDIR)
+CLEAN_FILES += $(KBUILD_SHELLCACHE)
 
 # Directories & files removed with 'make mrproper'
 MRPROPER_DIRS  += include/config usr/include include/generated          \
diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 0f82314621f2..e90e43fa3c81 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -7,6 +7,7 @@ quote   := "
 squote  := '
 empty   :=
 space   := $(empty) $(empty)
+tab     := $(empty)	$(empty)
 space_escape := _-_SPACE_-_
 
 ###
@@ -83,11 +84,35 @@ cc-cross-prefix =  \
 # output directory for tests below
 TMPOUT := $(if $(KBUILD_EXTMOD),$(firstword $(KBUILD_EXTMOD))/)
 
+KBUILD_SHELLCACHE := .shellcache
+
+ifeq ($(KBUILD_SHELLCACHE),)
+cached-shell = $(shell $(1))
+else
+-include $(KBUILD_SHELLCACHE)
+
+sanitize = $(subst $(space),_,	\
+	      $(subst $(tab),_,	\
+	      $(subst \n,_,	\
+	      $(subst :,_,	\
+	      $(subst \#,_,	\
+	      $(subst =,_,	\
+	      $(subst $$,_,	\
+	      $(subst ',_,	\
+	      $(subst ",_,	\
+	      $(1))))))))))
+
+cached-shell = $(if $(cmd$(call sanitize,$(1))),$(subst CACHED,,$(cmd$(call sanitize,$(1)))),$(shell \
+	res='$(shell $(1))';					\
+	echo "$$res";						\
+	echo 'cmd$(call sanitize,$(1)) = CACHED'"$$res" >> $(KBUILD_SHELLCACHE)))
+endif
+
 # try-run
 # Usage: option = $(call try-run, $(CC)...-o "$$TMP",option-ok,otherwise)
 # Exit code chooses option. "$$TMP" is can be used as temporary file and
 # is automatically cleaned up.
-try-run = $(shell set -e;		\
+try-run = $(call cached-shell,set -e;	\
 	TMP="$(TMPOUT).$$$$.tmp";	\
 	TMPO="$(TMPOUT).$$$$.o";	\
 	if ($(1)) >/dev/null 2>&1;	\
@@ -131,18 +156,19 @@ cc-disable-warning = $(call try-run,\
 
 # cc-name
 # Expands to either gcc or clang
-cc-name = $(shell $(CC) -v 2>&1 | grep -q "clang version" && echo clang || echo gcc)
+cc-name = $(call cached-shell,$(CC) -v 2>&1 | grep -q "clang version" && echo clang || echo gcc)
 
 # cc-version
-cc-version = $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-version.sh $(CC))
+cc-version = $(call cached-shell,$(CONFIG_SHELL) $(srctree)/scripts/gcc-version.sh $(CC))
 
 # cc-fullversion
-cc-fullversion = $(shell $(CONFIG_SHELL) \
+cc-fullversion = $(call cached-shell $(CONFIG_SHELL) \
 	$(srctree)/scripts/gcc-version.sh -p $(CC))
 
 # cc-ifversion
 # Usage:  EXTRA_CFLAGS += $(call cc-ifversion, -lt, 0402, -O1)
-cc-ifversion = $(shell [ $(cc-version) $(1) $(2) ] && echo $(3) || echo $(4))
+cc-ifversion = $(call cached-shell, \
+       [ $(cc-version) $(1) $(2) ] && echo $(3) || echo $(4))
 
 # cc-ldoption
 # Usage: ldflags += $(call cc-ldoption, -Wl$(comma)--hash-style=both)
@@ -161,11 +187,13 @@ ar-option = $(call try-run, $(AR) rc$(1) "$$TMP",$(1),$(2))
 
 # ld-version
 # Note this is mainly for HJ Lu's 3 number binutil versions
-ld-version = $(shell $(LD) --version | $(srctree)/scripts/ld-version.sh)
+ld-version = $(call cached-shell, \
+       $(LD) --version | $(srctree)/scripts/ld-version.sh)
 
 # ld-ifversion
 # Usage:  $(call ld-ifversion, -ge, 22252, y)
-ld-ifversion = $(shell [ $(ld-version) $(1) $(2) ] && echo $(3) || echo $(4))
+ld-ifversion = $(call cached-shell, \
+       [ $(ld-version) $(1) $(2) ] && echo $(3) || echo $(4))
 
 ######
 
-- 
2.8.1

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