From mboxrd@z Thu Jan 1 00:00:00 1970 From: Masahiro Yamada Date: Mon, 03 Feb 2014 12:46:30 +0900 Subject: [U-Boot] [PATCH v8 0/38] Switch over to real Kbuild In-Reply-To: References: <1390998395-18567-1-git-send-email-yamada.m@jp.panasonic.com> Message-ID: <20140203124630.481C.AA925319@jp.panasonic.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de Hello Simon and Tom, This is my analysis of Kbuild performance. [1] -j option is working What I must say first is -j option is working correctly with Kbuild. You can double-check by following the steps below. Apply Kbuild series v8 on commit 07e2822d158940a0e8ba45b6ab0344ffa1011a07. First, build without -j option. $ make mrproper $ time make CROSS_COMPILE=arm-linux-gnueabi- snow_config all Configuring for snow board... GEN include/autoconf.mk.dep [snip] real 1m15.089s user 0m44.092s sys 0m32.513s Next, build with -j8 option. (Run "make mrproper" every time because we want to be sure that there are no generated files before build.) $ make mrproper $ time make -j8 CROSS_COMPILE=arm-linux-gnueabi- snow_config all [snip] real 0m17.223s user 0m50.010s sys 0m29.038s It is much faster with -j8 option than without -j option. (4.3 times faster on my box.) You will easily notice another proof that -j option is working. If you do not add -j option, the shorten log will be displayed in the alphabetical order of output file name: LD arch/arm/cpu/built-in.o CC arch/arm/cpu/armv7/cache_v7.o CC arch/arm/cpu/armv7/cpu.o CC arch/arm/cpu/armv7/syslib.o CC arch/arm/cpu/armv7/s5p-common/cpu_info.o CC arch/arm/cpu/armv7/s5p-common/timer.o CC arch/arm/cpu/armv7/s5p-common/sromc.o CC arch/arm/cpu/armv7/s5p-common/pwm.o LD arch/arm/cpu/armv7/s5p-common/built-in.o LD arch/arm/cpu/armv7/built-in.o AS arch/arm/cpu/armv7/start.o CC arch/arm/cpu/armv7/exynos/clock.o CC arch/arm/cpu/armv7/exynos/power.o On the other hand, if you add -j option, the log will be shown in a different order: LD arch/arm/cpu/built-in.o CC arch/arm/cpu/armv7/cache_v7.o CC arch/arm/cpu/armv7/exynos/clock.o CC disk/part.o AS arch/arm/lib/crt0.o CC board/samsung/common/board.o CC board/samsung/smdk5250/smdk5250_spl.o CC common/main.o LD drivers/block/built-in.o LD board/samsung/common/built-in.o CC arch/arm/cpu/armv7/cpu.o AS arch/arm/lib/relocate.o CC disk/part_dos.o CC arch/arm/cpu/armv7/exynos/power.o [2] Is Kbuild slower than the old U-Boot build system? Yes, Kbuild is definitely slower. (But, as far as I tested, I don't think it is 3 times slower.) Let's compare the build time with the conventional build system. Checkout master branch. (commit 07e2822d158940a0e8ba45b6ab0344ffa1011a07) $ make mrproper $ time make CROSS_COMPILE=arm-linux-gnueabi- snow real 0m45.612s user 0m28.367s sys 0m18.969s So, Kbuild(=real 1m15.089s) is 1.6 times slower than the old U-Boot build system. [3] Why is Kbuild slower? One reason is "fixdep". The helper program, fixdep, parses the source file and all headers included from it to search all CONFIG macro used there. This is a rather heavy task. If you don't know the reason why "fixdep" is necessary, please read the comment block of scripts/basic/fixdep.c It is true that fixdep is meaningless for now, but it will be a great help when switching to Kconfig. We will get more return than we pay. (And Kconfig series is almost ready. I will test more and post version 1 within a couple of weeks.) Let' check how big the impact of fixdep is. I prepared a patch for you to disable fixdep: http://patchwork.ozlabs.org/patch/316057/ Apply it on commit 07e2822d158940a0e8ba45b6ab0344ffa1011a07 + Kbuild v8 And then, build. $ make mrproper $ time make CROSS_COMPILE=arm-linux-gnueabi- snow_config all real 1m2.436s user 0m38.281s sys 0m25.871s It is faster by 1.2 times faster without fixdep than it is with fixdep. Another big factor is "arg-check". This excellent routine is defined in scripts/Kbuild.include. The dependency tracking of U-Boot old build system is absolutely unreliable. It compares the timestamp between object files and source files, but never checks the arguments given to the compiler. Kbuild checks both of them to precisely detect which objects must be re-built. To see how heavy "arg-check" task is, build with KBUILD_NOCMDDEP=1 option to disable "arg-check". $ make mrproper $ time make CROSS_COMPILE=arm-linux-gnueabi- KBUILD_NOCMDDEP=1 snow_config all real 0m41.882s user 0m28.432s sys 0m14.971s See? It is as fast as the old U-boot system(=0m45.612) . Conclusion: The main reasons of the slow down with Kbuild are "fixdep" and "arg-check". Both of them are really important features for Kbuild and Kconfig. - "fixdep" is mandatory for our better life with Kconfig. - "arg-check" is for perfect dependency tracking. > > What's your plan about this series? > > Are we ready to switch to Kbuild, or need more review? > > Lets get the performance problem Simon found figured out, but then > otherwise, yes, I think we're about ready to merge. Tom, are you satisfied with my analisys? But, please hold merging Kbuild series. I will post version 9 with a little minor update. Best Regards Masahiro Yamada