On Fri, Apr 2, 2021 at 7:45 AM Elliot Berman <eberman@xxxxxxxxxxxxxx> wrote: > > If you update the timestamp of KCONFIG_CONFIG without actually changing > anything, config_data.gz is re-generated and causes vmlinux to re-link. > When Link Time Optimization is enabled, unnecessary re-linking of > vmlinux is highly desirable since it adds several minutes to build time. > > Avoid touching config_data.gz by using filechk to compare the existing > config_data.gz and update only if it changed. > > The .config can be touched, for instance, by a build script which > installs the default defconfig and then applies a defconfig fragment on > top. > > For a simple example on my x86 machine, I modified x86 default defconfig to set > CONFIG_IKCONFIG=y and run: > make -j50 defconfig tiny.config vmlinux > make -j50 defconfig tiny.config vmlinux > With this patch, vmlinux is not re-built as a result of config_data.gz > change. > > Signed-off-by: Elliot Berman <eberman@xxxxxxxxxxxxxx> > --- > kernel/Makefile | 2 +- > scripts/Makefile.lib | 2 ++ > 2 files changed, 3 insertions(+), 1 deletion(-) > > diff --git a/kernel/Makefile b/kernel/Makefile > index 320f1f3..bd4e558 100644 > --- a/kernel/Makefile > +++ b/kernel/Makefile > @@ -140,7 +140,7 @@ $(obj)/configs.o: $(obj)/config_data.gz > > targets += config_data.gz > $(obj)/config_data.gz: $(KCONFIG_CONFIG) FORCE > - $(call if_changed,gzip) > + $(call filechk,gzip) I do not think this is the right approach because gzip is executed every time, even if the time stamp is not changed. > > $(obj)/kheaders.o: $(obj)/kheaders_data.tar.xz > > diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib > index a4fbaf8..81d3ec1 100644 > --- a/scripts/Makefile.lib > +++ b/scripts/Makefile.lib > @@ -282,6 +282,8 @@ cmd_objcopy = $(OBJCOPY) $(OBJCOPYFLAGS) $(OBJCOPYFLAGS_$(@F)) $< $@ > quiet_cmd_gzip = GZIP $@ > cmd_gzip = cat $(real-prereqs) | $(KGZIP) -n -f -9 > $@ > > +filechk_gzip = cat $(real-prereqs) | $(KGZIP) -n -f -9 > + > # DTC > # --------------------------------------------------------------------------- > DTC ?= $(objtree)/scripts/dtc/dtc > -- > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, > a Linux Foundation Collaborative Project > -- Best Regards Masahiro Yamada
