| Message ID | 1617317072-26770-1-git-send-email-eberman@codeaurora.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Kbuild: Update config_data.gz only if KCONFIG_CONFIG materially changed | expand |
On Fri, Apr 2, 2021 at 7:45 AM Elliot Berman <eberman@codeaurora.org> 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@codeaurora.org> > --- > 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 >
On 4/2/2021 10:11 PM, Masahiro Yamada wrote: > On Fri, Apr 2, 2021 at 7:45 AM Elliot Berman <eberman@codeaurora.org> 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@codeaurora.org> >> --- >> 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. > Since .config is relatively small, gzip was quickly producing the same binary in multiple runs on my host. I thought about following gen_ikheaders.sh approach of comparing the md5sum, but I felt it was more complex than using filechk and re-compressing every time. I'll send a v2 tomorrow which follows gen_ikheaders.sh approach. > >> >> $(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 >>
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) $(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
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@codeaurora.org> --- kernel/Makefile | 2 +- scripts/Makefile.lib | 2 ++ 2 files changed, 3 insertions(+), 1 deletion(-)