kbuild: create directory for make cache only when necessary

Currently, the existence of $(dir $(make-cache)) is always checked,
and created if it is missing.

We can avoid unnecessary system calls by some tricks.

[1] If KBUILD_SRC is unset, we are building in the source tree.
    The output directory checks can be entirely skipped.
[2] If at least one cache data is found, it means the cache file
    was included.  Obviously its directory exists.  Skip "mkdir -p".
[3] If Makefile does not contain any call of __run-and-store, it will
    not create a cache file.  No need to create its directory.
[4] The "mkdir -p" should be only invoked by the first call of
    __run-and-store

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
This commit is contained in:
Masahiro Yamada 2017-11-13 19:29:34 +09:00
parent 859fd5860c
commit 9a234a2e38

View File

@ -99,18 +99,19 @@ cc-cross-prefix = \
# Include values from last time
make-cache := $(if $(KBUILD_EXTMOD),$(KBUILD_EXTMOD)/,$(if $(obj),$(obj)/)).cache.mk
ifeq ($(wildcard $(dir $(make-cache))),)
$(shell mkdir -p '$(dir $(make-cache))')
endif
$(make-cache): ;
-include $(make-cache)
cached-data := $(filter __cached_%, $(.VARIABLES))
# If cache exceeds 1000 lines, shrink it down to 500.
ifneq ($(word 1000,$(filter __cached_%, $(.VARIABLES))),)
ifneq ($(word 1000,$(cached-data)),)
$(shell tail -n 500 $(make-cache) > $(make-cache).tmp; \
mv $(make-cache).tmp $(make-cache))
endif
create-cache-dir := $(if $(KBUILD_SRC),$(if $(cache-data),,1))
# Usage: $(call __sanitize-opt,Hello=Hola$(comma)Goodbye Adios)
#
# Convert all '$', ')', '(', '\', '=', ' ', ',', ':' to '_'
@ -136,6 +137,10 @@ __sanitize-opt = $(subst $$,_,$(subst $(right_paren),_,$(subst $(left_paren),_,$
define __run-and-store
ifeq ($(origin $(1)),undefined)
$$(eval $(1) := $$(shell $$(2)))
ifeq ($(create-cache-dir),1)
$$(shell mkdir -p $(dir $(make-cache)))
$$(eval create-cache-dir :=)
endif
$$(shell echo '$(1) := $$($(1))' >> $(make-cache))
endif
endef