linux-kernel - Re: [PATCH] kbuild: pass jobserver to cmd_ld

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Message-ID: <CAKwvOdmb5xdF70TzNp=4STCpzkGh16FnuKE1KbdzDhHt=OuRFA@mail.gmail.com>
Date:   Fri, 17 Jun 2022 09:32:15 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Sedat Dilek <sedat.dilek@...il.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Jiri Slaby <jslaby@...e.cz>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nathan Chancellor <nathan@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: Re: [PATCH] kbuild: pass jobserver to cmd_ld_vmlinux.o

On Fri, Jun 17, 2022 at 3:35 AM Sedat Dilek <sedat.dilek@...il.com> wrote:
>
> On Fri, Jun 17, 2022 at 12:53 AM Sedat Dilek <sedat.dilek@...il.com> wrote:
> >
> > On Thu, Jun 16, 2022 at 4:09 PM Sedat Dilek <sedat.dilek@...il.com> wrote:
> > >
> > > On Thu, Jun 16, 2022 at 12:45 PM Jiri Slaby <jslaby@...e.cz> wrote:
> > > >
> > > > Until the link-vmlinux.sh split (cf. the commit below), the linker was
> > > > run with jobserver set in MAKEFLAGS. After the split, the command in
> > > > Makefile.vmlinux_o is not prefixed by "+" anymore, so this information
> > > > is lost.
> > > >
> > > > Restore it as linkers working in parallel (esp. the LTO ones) make a use
> > > > of it.

TBH, I agree with Masahiro. I didn't understand this comment "esp. the
LTO ones."  Jiri, can you clarify what you mean here?

> [ CC Nathan and Sami ]
>
> I re-checked as my build-time takes approx. 15mins more than usual
> with Linux v5.17.
>
> [ Perf - seconds time elapsed ]
> v5.17: approx. 12500
> v5.19: approx. 13500
>
> +1.000 secs = +16,67mins

Does this patch make a difference?
https://lore.kernel.org/linux-kbuild/20220616195759.3214538-1-samitolvanen@google.com/

-- 
Thanks,
~Nick Desaulniers