Hi Casey, 2018-08-23 21:14 GMT+09:00 Casey Fitzpatrick <kcghost@xxxxxxxxx>: > Masahiro, > > Thanks, I was not aware of that patch. That does fix the issue for the > most part. A rebuild now consistently does the same work, and does not > unnecessarily update the timestamp of bzImage as before. It still > takes 3 seconds, but maybe that is necessary? I don't know exactly > what it is doing there. Yes. The build log looks reasonable, and some seconds is typical necessary for rebuilding with no update. > time make -j16 bzImage > CHK include/config/kernel.release > CHK include/generated/uapi/linux/version.h > DESCEND objtool > CHK include/generated/utsrelease.h > CHK scripts/mod/devicetable-offsets.h > CHK include/generated/timeconst.h > CHK include/generated/bounds.h > CHK include/generated/asm-offsets.h > CALL scripts/checksyscalls.sh > CHK include/generated/compile.h > Kernel: arch/x86/boot/bzImage is ready (#1) > > real 0m3.027s > user 0m11.183s > sys 0m4.755s > stat --printf 'mtime: %y\n' arch/x86/boot/bzImage > mtime: 2018-08-23 08:04:55.551644635 -0400 > time make -j16 bzImage > CHK include/config/kernel.release > CHK include/generated/uapi/linux/version.h > DESCEND objtool > CHK include/generated/utsrelease.h > CHK scripts/mod/devicetable-offsets.h > CHK include/generated/timeconst.h > CHK include/generated/bounds.h > CHK include/generated/asm-offsets.h > CALL scripts/checksyscalls.sh > CHK include/generated/compile.h > Kernel: arch/x86/boot/bzImage is ready (#1) > > real 0m2.966s > user 0m10.917s > sys 0m4.834s > stat --printf 'mtime: %y\n' arch/x86/boot/bzImage > mtime: 2018-08-23 08:04:55.551644635 -0400 > time make -j16 bzImage > CHK include/config/kernel.release > CHK include/generated/uapi/linux/version.h > DESCEND objtool > CHK include/generated/utsrelease.h > CHK scripts/mod/devicetable-offsets.h > CHK include/generated/timeconst.h > CHK include/generated/bounds.h > CHK include/generated/asm-offsets.h > CALL scripts/checksyscalls.sh > CHK include/generated/compile.h > Kernel: arch/x86/boot/bzImage is ready (#1) > > real 0m2.954s > user 0m11.151s > sys 0m4.734s > stat --printf 'mtime: %y\n' arch/x86/boot/bzImage > mtime: 2018-08-23 08:04:55.551644635 -0400 > > Sincerely, > Casey Fitzpatrick > On Wed, Aug 22, 2018 at 9:54 PM Masahiro Yamada > <yamada.masahiro@xxxxxxxxxxxxx> wrote: >> >> Hi Casey, >> >> 2018-08-23 8:21 GMT+09:00 Casey Fitzpatrick <kcghost@xxxxxxxxx>: >> > I have observed that attempting to rebuild the kernel with no changes >> > to source files: >> > 1. Takes more time than I should hope is necessary; I would hope it >> > would only check timestamps and determine the target does not need >> > updating rather than do work. >> > 2. Switches between two states of determining what work is needed to do. >> > 3. Unnecessarily updates timestamp on bzImage (and maybe others) >> > despite not actually modifying the file. >> > >> > I am working with v4.14.66 building from an Ubuntu 17.10 machine. >> > The following summarized output demonstrates the issue (I believe the >> > same happens with the default target). >> > Notice that despite no changes made to sources, a rebuild takes 3 >> > seconds on my machine, does some work and typically updates the >> > timestamp of the target. >> > Also notice that the work is oddly inconsistent, the third time I ran >> > the same build with no changes it did different work. And in that case >> > it does not update the timestamp of the target, which is preferable. >> > >> > make distclean >> > make x86_64_defconfig >> > time make -j16 bzImage >> > ...(lots of output, actually building all the sources) >> > OBJCOPY arch/x86/boot/setup.bin >> > BUILD arch/x86/boot/bzImage >> > Setup is 15548 bytes (padded to 15872 bytes). >> > System is 7789 kB >> > CRC 5b2b5059 >> > Kernel: arch/x86/boot/bzImage is ready (#1) >> > >> > real 4m15.147s >> > user 27m21.182s >> > sys 2m34.607s >> > stat --printf 'mtime: %y\n' arch/x86/boot/bzImage >> > mtime: 2018-08-22 18:57:10.000000000 -0400 >> > time make -j16 bzImage >> > CHK include/config/kernel.release >> > CHK include/generated/uapi/linux/version.h >> > DESCEND objtool >> > CHK scripts/mod/devicetable-offsets.h >> > CHK include/generated/utsrelease.h >> > CHK include/generated/timeconst.h >> > CHK include/generated/bounds.h >> > CHK include/generated/asm-offsets.h >> > CALL scripts/checksyscalls.sh >> > CHK include/generated/compile.h >> > DATAREL arch/x86/boot/compressed/vmlinux >> > BUILD arch/x86/boot/bzImage >> > Setup is 15548 bytes (padded to 15872 bytes). >> > System is 7789 kB >> > CRC 5b2b5059 >> > Kernel: arch/x86/boot/bzImage is ready (#1) >> > >> > real 0m3.273s >> > user 0m11.260s >> > sys 0m4.727s >> > stat --printf 'mtime: %y\n' arch/x86/boot/bzImage >> > mtime: 2018-08-22 19:00:26.587233951 -0400 >> > time make -j16 bzImage >> > CHK include/config/kernel.release >> > CHK include/generated/uapi/linux/version.h >> > DESCEND objtool >> > CHK include/generated/utsrelease.h >> > CHK scripts/mod/devicetable-offsets.h >> > CHK include/generated/timeconst.h >> > CHK include/generated/bounds.h >> > CHK include/generated/asm-offsets.h >> > CALL scripts/checksyscalls.sh >> > CHK include/generated/compile.h >> > LD arch/x86/boot/compressed/vmlinux >> > ZOFFSET arch/x86/boot/zoffset.h >> > OBJCOPY arch/x86/boot/vmlinux.bin >> > AS arch/x86/boot/header.o >> > LD arch/x86/boot/setup.elf >> > OBJCOPY arch/x86/boot/setup.bin >> > BUILD arch/x86/boot/bzImage >> > Setup is 15548 bytes (padded to 15872 bytes). >> > System is 7789 kB >> > CRC 5b2b5059 >> > Kernel: arch/x86/boot/bzImage is ready (#1) >> > >> > real 0m3.136s >> > user 0m11.411s >> > sys 0m4.775s >> > stat --printf 'mtime: %y\n' arch/x86/boot/bzImage >> > mtime: 2018-08-22 19:01:11.583377706 -0400 >> > time make -j16 bzImage >> > CHK include/config/kernel.release >> > CHK include/generated/uapi/linux/version.h >> > DESCEND objtool >> > CHK include/generated/utsrelease.h >> > CHK scripts/mod/devicetable-offsets.h >> > CHK include/generated/timeconst.h >> > CHK include/generated/bounds.h >> > CHK include/generated/asm-offsets.h >> > CALL scripts/checksyscalls.sh >> > CHK include/generated/compile.h >> > DATAREL arch/x86/boot/compressed/vmlinux >> > Kernel: arch/x86/boot/bzImage is ready (#1) >> > >> > real 0m3.118s >> > user 0m11.476s >> > sys 0m4.505s >> > stat --printf 'mtime: %y\n' arch/x86/boot/bzImage >> > mtime: 2018-08-22 19:01:11.583377706 -0400 >> > >> > Sincerely, >> > Casey Fitzpatrick >> >> >> >> Could you check if the following commit fixes the problem? >> >> >> commit 92a4728608a8fd228c572bc8ff50dd98aa0ddf2a >> Author: Kees Cook <keescook@xxxxxxxxxxxx> >> Date: Tue Jul 24 16:08:27 2018 -0700 >> >> x86/boot: Fix if_changed build flip/flop bug >> >> >> >> >> I am not sure whether it was back-ported to 4.14 kernel or not... >> >> >> >> >> >> >> -- >> Best Regards >> Masahiro Yamada -- Best Regards Masahiro Yamada
