linux-kernel - Re: [PATCH v6 00/18] Implement DWARF modversions

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Message-ID: <CABCJKudwpKX1_j46Tp6=eAJ0JU2zWE15+c8OFq9LMAnSqwesOw@mail.gmail.com>
Date: Mon, 25 Nov 2024 11:34:30 +0200
From: Sami Tolvanen <samitolvanen@...gle.com>
To: sedat.dilek@...il.com
Cc: Masahiro Yamada <masahiroy@...nel.org>, Luis Chamberlain <mcgrof@...nel.org>, 
	Miguel Ojeda <ojeda@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Matthew Maurer <mmaurer@...gle.com>, Alex Gaynor <alex.gaynor@...il.com>, Gary Guo <gary@...yguo.net>, 
	Petr Pavlu <petr.pavlu@...e.com>, Daniel Gomez <da.gomez@...sung.com>, Neal Gompa <neal@...pa.dev>, 
	Hector Martin <marcan@...can.st>, Janne Grunau <j@...nau.net>, Miroslav Benes <mbenes@...e.cz>, 
	Asahi Linux <asahi@...ts.linux.dev>, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org, 
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v6 00/18] Implement DWARF modversions

Hi,

On Sat, Nov 23, 2024 at 1:23 PM Sedat Dilek <sedat.dilek@...il.com> wrote:
>
> > BTW, I am testing with the latest kmod-git and pahole-git.
> >
> > I will give this a try when Linux v6.12.1 is released.
> >
>
> I have a prolonged build-time of +22,75 per cent.
> Compared gendwarfksyms-v5 + Linux-v6.12.0 VS. gendwarfksyms-v6 + Linux-v6.12.1
>
> Is this a known issue?

In my tests, compared to a genksyms defconfig build with debugging
information, v5 was slightly faster, and v6 was 5.6% slower. This is
because the expansion limits were dropped in this version to ensure
version stability when exports are removed. See the explanation here:

https://lore.kernel.org/linux-modules/20241120215454.GA3512979@google.com/

I did profile this quickly and most of the time seems to be spent in
libdw looking up attributes. We might be able to speed this up by
limiting the number of attributes we look up depending on the DIE
type, but I haven't had time to look into it yet. I'll take a closer
look when I'm back from my vacation in about three weeks.

Sami