linux-kernel - Re: [PATCH] kbuild: revive parallel execution for .tmp

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Date:   Mon, 14 Nov 2022 17:18:34 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kbuild: revive parallel execution for .tmp_initcalls.lds
 rule

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@...nel.org>

Reviewed-by: Nathan Chancellor <nathan@...nel.org>

At least it doesn't seem like compile times were majorly affected. I
benchmarked arm64 allmodconfig (worst case scenario with ThinLTO):

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
>