linux-kernel - Re: [PATCH v1 0/7] DCE/DSE: Add Dead Syscalls Elimination support, part1

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Message-Id: <fbb6f526-0db9-4bbe-9635-8cb55b4335ee@app.fastmail.com>
Date:   Tue, 26 Sep 2023 09:14:11 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Zhangjin Wu" <falcon@...ylab.org>, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-riscv@...ts.infradead.org
Cc:     "Palmer Dabbelt" <palmer@...osinc.com>,
        "Paul Walmsley" <paul.walmsley@...ive.com>, paulburton@...nel.org,
        "Paul E. McKenney" <paulmck@...nel.org>,
        "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>,
        "Willy Tarreau" <w@....eu>,
        Thomas Weißschuh <linux@...ssschuh.net>,
        "Tim Bird" <tim.bird@...y.com>,
        "Geert Uytterhoeven" <geert@...ux-m68k.org>,
        "Nicolas Pitre" <nico@...xnic.net>
Subject: Re: [PATCH v1 0/7] DCE/DSE: Add Dead Syscalls Elimination support, part1

On Tue, Sep 26, 2023, at 00:33, Zhangjin Wu wrote:
>
> This series aims to add DCE based DSE support, here is the first
> revision of the RFC patchset [1], the whole series includes three parts,
> here is the Part1.
>
> This Part1 adds basic DCE based DSE support.
>
> Part2 will further eliminate the unused syscalls forcely kept by the
> exception tables.
>
> Part3 will add DSE test support with nolibc-test.c.

I missed the RFC version, but I think this is a useful thing to
have overall, though it will probably need to go through a couple
of revisions and rewrites, mostly to ensure we are not adding
complexity that gets in the way of other improvements I would
like to see to the syscall entry handling.

It would be nice to include some size numbers here for at least
one practical use case. If you have a defconfig for a shipping
product with a small kernel, what is the 'size -B' output you
see comparing with and without DCE and, and with DCE+DSE?

There is generally not much work going into micro-optimizing
the size of the kernel image any more, for a number of reasons,
but if you are able to show that this is a noticeable improvement,
we should be able to find a way to do it. Geert is doing statistics
about size bloat over time, and anything that undoes a couple
of years worth of bloat would clearly be significant here.

Another alternative would be to resume the work done by Nicolas
Pitre, who added Kconfig symbols for controlling groups of
system calls. Since we already have a number of those compile
time options, adding more of them should generally be
less controversial and more consistent, while bringing most
of the same benefits.

     Arnd