linux-kernel - Re: [PATCH] [RFC, DO NOT APPLY] vmlinux.lds: revert link speed regression

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Message-ID: <CAF1bQ=Qk7pRWUxAcZNPjFquukHpXgi=34NmMbuRBAwv5+KcWtQ@mail.gmail.com>
Date: Tue, 21 Jan 2025 09:36:04 -0800
From: Rong Xu <xur@...gle.com>
To: Arnd Bergmann <arnd@...db.de>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Arnd Bergmann <arnd@...nel.org>, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, regressions@...ts.linux.dev, 
	Han Shen <shenhan@...gle.com>, Nathan Chancellor <nathan@...nel.org>, Kees Cook <kees@...nel.org>, 
	Jann Horn <jannh@...gle.com>, Ard Biesheuvel <ardb@...nel.org>, 
	Linux-Arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH] [RFC, DO NOT APPLY] vmlinux.lds: revert link speed regression

On Mon, Jan 20, 2025 at 11:42 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Tue, Jan 21, 2025, at 01:19, Masahiro Yamada wrote:
> > On Tue, Jan 21, 2025 at 6:29 AM Arnd Bergmann <arnd@...nel.org> wrote:
> >>
> >>                 linux-6.12      linux-6.13
> >> ld.lld v20      1.2s            1.2s
> >> ld.bfd v2.36    3.2s            5.2s
> >> ld.bfd v2.39    59s             388s
> >>
> >
> > Is this problem specific to the BFD linker from binutils?
>
> I only tried the bfd and lld linkers, but I assume it's limited
> to the bfd one.
>
> > Did you observe a link speed regression with LLVM=1 build?
>
> No, the ld.lld line above is what I see with LLVM=1, it's
> very fast (1.2s) both before and after the change. New
> ld.bfd versions were much slower before the regression
> for this particular config and got even slower (seven minutes
> for each of the three vmlinux link stages).
>

Can you send me the instructions to reproduce?
I'm seeing a significant performance drop (18.5x slow down) with
ld.bfd v2.39 when
linking linux-6.12 (i.e without this change)

I will take a look at ld.bfd. It looks like an ld.bfd issue.

-Rong

>       Arnd