linux-kernel - Re: [RFC 13/13] m68k: mac: convert to generic clockevent

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Date:   Fri, 23 Oct 2020 11:24:36 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Finn Thain <fthain@...egraphics.com.au>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Russell King <linux@...linux.org.uk>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Philip Blundell <philb@....org>,
        Joshua Thompson <funaho@...ai.org>,
        Sam Creasey <sammy@...my.net>,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        John Stultz <john.stultz@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        "linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
        Parisc List <linux-parisc@...r.kernel.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC 13/13] m68k: mac: convert to generic clockevent

Hi Arnd,

On Fri, Oct 23, 2020 at 9:52 AM Arnd Bergmann <arnd@...nel.org> wrote:
> On Sun, Oct 18, 2020 at 2:55 AM Finn Thain <fthain@...egraphics.com.au> wrote:
> > On Thu, 15 Oct 2020, Arnd Bergmann wrote:
> > > On Thu, Oct 15, 2020 at 3:19 AM Finn Thain <fthain@...egraphics.com.au> wrote:
> > > > On Sat, 10 Oct 2020, Arnd Bergmann wrote:
> >
> > That configuration still produces the same 5 KiB of bloat. I see that
> > kernel/time/Kconfig has this --
> >
> > # Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is
> > # only related to the tick functionality. Oneshot clockevent devices
> > # are supported independent of this.
> > config TICK_ONESHOT
> >         bool
> >
> > But my question was really about both kinds of dead code (oneshot device
> > support and oneshot tick support). Anyway, after playing with the code for
> > a bit I don't see any easy way to reduce the growth in text size.
>
> Did you look more deeply into where those 5KB are? Is this just
> the code in kernel/time/{clockevents,tick-common}.c and the
> added platform specific bits, or is there something more?
> I suppose the sysfs interface and the clockevents_update_freq()
> logic are not really needed on m68k, but it wouldn't make much
> sense to split those out either.
>
> How does the 5KB bloat compare to the average bloat we get
> from one release to the next? Geert has been collecting statistics
> for this.

It would be a fair share of the typical increase of ca. 30 KiB per
kernel release. Still, it would be lost in the noise of the increase for
v5.10-rc1:

    add/remove: 1200/455 grow/shrink: 1419/821 up/down: 468970/-93714 (375256)
    Function                                     old     new   delta
    _printk_rb_static_infos                        -  180224 +180224
    write_buf                                   8192   32768  +24576
    _printk_rb_static_descs                        -   24576  +24576
    HUF_decompress4X4_usingDTable_internal         -    5664   +5664
    HUF_decompress4X2_usingDTable_internal         -    5006   +5006
    __ext4_ioctl                                   -    4774   +4774
    sock_ops_convert_ctx_access                 3840    8462   +4622
    ZSTD_decompressSequences                       -    3100   +3100

> > > The arm/rpc timer seems to be roughly in the same category as most of
> > > the m68k ones or the i8253 counter on a PC. It's possible that some of
> > > them could use the same logic as drivers/clocksource/i8253.o as long as
> > > there is any hardware oneshot mode.
> >
> > There appear to be 15 platforms in that category. 4 have no clocksource
> > besides the jiffies clocksource, meaning there's no practical alternative
> > to using a periodic tick, like you did in your RFC patch:
> >
> > arch/m68k/apollo/config.c
> > arch/m68k/q40/q40ints.c
> > arch/m68k/sun3/sun3ints.c
> > arch/m68k/sun3x/time.c
>
> Do any of these have users? I'm fairly sure sun3x has never worked in mainline,
> sun3 seems to still need the same few patches it did 20 years ago. I
> couldn't find
> much about Linux on Apollo or q40, the information on the web for either
> of them seems to all be for linux-2.4 kernels.

They probably don't have any users.
AFAIK, the only users are the usual triumvirate of amiga/atari/mac
(and perhaps the fleet of VME boards in the Australian navy? ;)

Gr{oetje,eeting}s,

                        Geert


--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds