Re: m68k 2.6.26-1 vs 2.4.30 comparison

[Geert Uytterhoeven <geert.uytterhoeven@gmail.com>]

On Sun, May 3, 2009 at 09:28, Lance Tagliapietra <lancetag@luminet.net> wrote:
> b). My custom 2.4.30 kernel size is about 750K uncompressed. With setting the options to
> remove support for hardware that I don't have and features that I don't need, I still
> came up with a kernel of 2.7M.  The goal is to have the smallest footprint kernel possible.

Yeah, minimum kernel size has increased :-(

> c). The 2.6.26 kernel seems to want to keep more memory free and hit the swap much more
> than the 2.4.30 kernel according to vmstat.  Under 2.4.30 I see the free memory go as low
> as about 200K, and it will remain at that level as long as is necessary.  Under 2.6.26,
> the free memory stays at about 800K, and if it drops below that, it will come back to that
> level relatively quickly.

As memory consumption is general. I didn't do exact measurements, but
2.6 consumes ca. 1.5 MiB
more on my A4000 (with 12 MiB of fast RAM). Booting and running Debian
is slow, while I used to
have more daemons installed, in a time the machine was actually used
as a mailserver for 70 people,
some of which read their email by logging in and running pine...

> d). The real time clock came up on the worng month, going from 2.4.30 to 2.6.26 (or 28),
> March vs April, in this case.

That's an interesting one...

In 2.4.30, you have both a2000_gettod() (for boot time setting), which does:

    *monp  = tod_2000.month1      * 10 + tod_2000.month2;

and amiga_hwclk() (for /dev/rtc), which does:

    t->tm_mon  = tod_2000.month1      * 10 + tod_2000.month2 - 1;

In 2.6.29, you only have a2000_hwclk(), which does

    t->tm_mon  = tod_2000.month1      * 10 + tod_2000.month2 - 1;

The data returned by a2000_gettod() is converted to seconds using mktime(),
which assumes months are in the range 1..12.

amiga_hwclk() and a2000_hwclk() both use struct rtc_time. This should
be similar to
struct tm in <time.h>, where the months are in the range 0..11.
Both rtc_proc_output()/gen_rtc_proc_output() (2.4.30) and
rtc_proc_show() (2.6.29) do
print tm.tm_mon + 1 to make them be in the range 1..12.

So at first sight, I don't see where the bug is...

What does `hwlock -ur` say, on both 2.4.30 and 2.6.29?

> Questions:
>
> e). Is there an option which tells the kernel the minimum amount of free RAM to maintain
> as I describe in (c) above?  RAM is relatively precious in my m68k environment, and having
> 500k being held in reserve seems a bit much?

Probably one of those swappiness parameters under /sys. Don't ask me
which one...

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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
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