On Tue, Nov 15, 2022 at 9:18 AM Nathan Chancellor <nathan@xxxxxxxxxx> wrote:
>
> On Tue, Nov 15, 2022 at 02:46:17AM +0900, Masahiro Yamada wrote:
> > Prior to commit 5d45950dfbb1 ("kbuild: move vmlinux.o link to
> > scripts/Makefile.vmlinux_o"), jobserver-exec was invoked from the shell
> > script, link-vmlinux.sh. It can get access to the jobserver because
> > Makefile adds '+' prefix, as in:
> >
> > +$(call if_changed_dep,link_vmlinux)
> >
> > Since 5d45950dfbb1, jobserver-exec is invoked from Makefile, but the
> > '+' prefix is missing, hence jobserver-exec has no access to the
> > jobserver.
> >
> > Fixes: 5d45950dfbb1 ("kbuild: move vmlinux.o link to scripts/Makefile.vmlinux_o")
> > Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
>
> Reviewed-by: Nathan Chancellor <nathan@xxxxxxxxxx>
>
> At least it doesn't seem like compile times were majorly affected. I
> benchmarked arm64 allmodconfig (worst case scenario with ThinLTO):
Ah, sorry.
./scripts/generate_initcall_order.pl always runs in two threads
(the parent and a single child) because it is given only
one argument (vmlinux.a).
So, using jobserver-exec is meaningless.
Also, the code for parallel execution control in
./scripts/generate_initcall_order.pl is meaningless.
BTW, allmodconfig is not the worst case because most of the objects
go into modules instead of vmlinux.
allyesconfig would add more symbols to vmlinux although I did not test it.
>
> Benchmark 1: 094226ad94f4 ("Linux 6.1-rc5")
> Time (mean ± σ): 899.036 s ± 1.133 s [User: 49314.495 s, System: 3840.796 s]
> Range (min … max): 898.118 s … 900.302 s 3 runs
>
> Benchmark 2: 0f45cbb5399b ("kbuild: revive parallel execution for .tmp_initcalls.lds rule")
> Time (mean ± σ): 898.482 s ± 0.152 s [User: 49329.703 s, System: 3836.408 s]
> Range (min … max): 898.306 s … 898.584 s 3 runs
>
> Summary
> '0f45cbb5399b ("kbuild: revive parallel execution for .tmp_initcalls.lds rule")' ran
> 1.00 ± 0.00 times faster than '094226ad94f4 ("Linux 6.1-rc5")'
>
> > ---
> >
> > scripts/Makefile.vmlinux_o | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/scripts/Makefile.vmlinux_o b/scripts/Makefile.vmlinux_o
> > index 0edfdb40364b..ae52d3b3f063 100644
> > --- a/scripts/Makefile.vmlinux_o
> > +++ b/scripts/Makefile.vmlinux_o
> > @@ -19,7 +19,7 @@ quiet_cmd_gen_initcalls_lds = GEN $@
> >
> > .tmp_initcalls.lds: $(srctree)/scripts/generate_initcall_order.pl \
> > vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
> > - $(call if_changed,gen_initcalls_lds)
> > + +$(call if_changed,gen_initcalls_lds)
> >
> > targets := .tmp_initcalls.lds
> >
> > --
> > 2.34.1
> >
--
Best Regards
Masahiro Yamada
