| Message ID | 1547436479-10491-1-git-send-email-yamada.masahiro@socionext.com |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] kbuild: remove top-level built-in.a | expand |
Masahiro Yamada's on January 14, 2019 1:27 pm: > The symbol table in the final archive is unneeded because it is passed > to the linker after the --whole-archive option. Every object file in > the archive is included in the link anyway. > > Pass thin archives from subdirectories directly to the linker, and > remove the final archiving step. This seems like a good improvement. As far as I remember, it was slower to do the final link without the index built. Maybe I was testing it in a revision before moving those files into --whole-archive? If there is no slowdown, then I have no objection. Acked-by: Nicholas Piggin <npiggin@gmail.com>
Hi Nicholas, On Tue, Jan 15, 2019 at 5:07 PM Nicholas Piggin <npiggin@gmail.com> wrote: > > Masahiro Yamada's on January 14, 2019 1:27 pm: > > The symbol table in the final archive is unneeded because it is passed > > to the linker after the --whole-archive option. Every object file in > > the archive is included in the link anyway. > > > > Pass thin archives from subdirectories directly to the linker, and > > remove the final archiving step. > > This seems like a good improvement. As far as I remember, it was slower > to do the final link without the index built. Maybe I was testing it > in a revision before moving those files into --whole-archive? If there > is no slowdown, then I have no objection. Thanks for the review. I measured the performance of scripts/link-vmlinux.sh with 'perf stat'. (20 times for each) Before this patch: Performance counter stats for 'make vmlinux' (20 runs): 5.266796537 seconds time elapsed ( +- 0.12% ) After this patch: Performance counter stats for 'make vmlinux' (20 runs): 4.945576395 seconds time elapsed So, the performance is slightly better. Maybe, does omitting the 'ar' save some time? Anyway, this commit is good. -- Best Regards Masahiro Yamada
Masahiro Yamada's on January 15, 2019 7:01 pm: > Hi Nicholas, > > > On Tue, Jan 15, 2019 at 5:07 PM Nicholas Piggin <npiggin@gmail.com> wrote: >> >> Masahiro Yamada's on January 14, 2019 1:27 pm: >> > The symbol table in the final archive is unneeded because it is passed >> > to the linker after the --whole-archive option. Every object file in >> > the archive is included in the link anyway. >> > >> > Pass thin archives from subdirectories directly to the linker, and >> > remove the final archiving step. >> >> This seems like a good improvement. As far as I remember, it was slower >> to do the final link without the index built. Maybe I was testing it >> in a revision before moving those files into --whole-archive? If there >> is no slowdown, then I have no objection. > > > Thanks for the review. > > > I measured the performance of scripts/link-vmlinux.sh with 'perf stat'. > (20 times for each) > > > > Before this patch: > > Performance counter stats for 'make vmlinux' (20 runs): > > 5.266796537 seconds time elapsed > ( +- 0.12% ) > > > > After this patch: > > Performance counter stats for 'make vmlinux' (20 runs): > > 4.945576395 seconds time elapsed > > > > > So, the performance is slightly better. > > Maybe, does omitting the 'ar' save some time? Wow yeah that's a good speedup and simplification to boot. Thanks for checking it. > Anyway, this commit is good. Yes, it's a good improvement. Thanks, Nick
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh index c8cf453..4788def 100755 --- a/scripts/link-vmlinux.sh +++ b/scripts/link-vmlinux.sh @@ -44,24 +44,6 @@ info() fi } -# Thin archive build here makes a final archive with symbol table and indexes -# from vmlinux objects INIT and MAIN, which can be used as input to linker. -# KBUILD_VMLINUX_LIBS archives should already have symbol table and indexes -# added. -# -# Traditional incremental style of link does not require this step -# -# built-in.a output file -# -archive_builtin() -{ - info AR built-in.a - rm -f built-in.a; - ${AR} rcsTP${KBUILD_ARFLAGS} built-in.a \ - ${KBUILD_VMLINUX_INIT} \ - ${KBUILD_VMLINUX_MAIN} -} - # Link of vmlinux.o used for section mismatch analysis # ${1} output file modpost_link() @@ -69,7 +51,8 @@ modpost_link() local objects objects="--whole-archive \ - built-in.a \ + ${KBUILD_VMLINUX_INIT} \ + ${KBUILD_VMLINUX_MAIN} \ --no-whole-archive \ --start-group \ ${KBUILD_VMLINUX_LIBS} \ @@ -88,7 +71,8 @@ vmlinux_link() if [ "${SRCARCH}" != "um" ]; then objects="--whole-archive \ - built-in.a \ + ${KBUILD_VMLINUX_INIT} \ + ${KBUILD_VMLINUX_MAIN} \ --no-whole-archive \ --start-group \ ${KBUILD_VMLINUX_LIBS} \ @@ -99,7 +83,8 @@ vmlinux_link() -T ${lds} ${objects} else objects="-Wl,--whole-archive \ - built-in.a \ + ${KBUILD_VMLINUX_INIT} \ + ${KBUILD_VMLINUX_MAIN} \ -Wl,--no-whole-archive \ -Wl,--start-group \ ${KBUILD_VMLINUX_LIBS} \ @@ -160,7 +145,6 @@ cleanup() rm -f .tmp_System.map rm -f .tmp_kallsyms* rm -f .tmp_vmlinux* - rm -f built-in.a rm -f System.map rm -f vmlinux rm -f vmlinux.o @@ -217,8 +201,6 @@ fi; # final build of init/ ${MAKE} -f "${srctree}/scripts/Makefile.build" obj=init -archive_builtin - #link vmlinux.o info LD vmlinux.o modpost_link vmlinux.o
The symbol table in the final archive is unneeded because it is passed to the linker after the --whole-archive option. Every object file in the archive is included in the link anyway. Pass thin archives from subdirectories directly to the linker, and remove the final archiving step. Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> --- scripts/link-vmlinux.sh | 30 ++++++------------------------ 1 file changed, 6 insertions(+), 24 deletions(-) -- 2.7.4