Re: m68k 2.6.26-1 vs 2.4.30 comparison

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On Wed, May 06, 2009 at 08:44:41AM +0200, Kolbj??rn Barmen wrote:
On Sun, 3 May 2009, Lance Tagliapietra wrote:

Observations: a). I 2.4.30 kernel compile was about 6 hours on this hardware (GCC 2.95.4).  The 2.6.29 took 4 days 
(GCC 4.1.2, Debian).  That was without the modules, too.  Now, it did select the config option for smallest code 
size, and perhaps that is not well supported for m68k and also added to the compile time. Make was done as nice -n 
17 but the system is mostly idle, otherwise, but that is how I compile the 2.4.30.

Most of the times is spent "entering directory bla; : nothing to do here; leaving directory bla" - 2.6 is much bigger 
in terms of number of directories/files to parse through, and on slow IO that certainly matters :)

Also, what seemed to be different is that this compile called a shell script for each file being compiled.  I'm not sure 
if that was generated by the Makefile at build time yet.  My other thought is that GCC 4.1.x has a larger footprint than 
GCC 2.95 as it seemed to swap more than under the 2.4.30 / GCC 2.95.x.


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.

My amiga kernel, which is not optimized for size, has ipv6 and lots of stuff,, is 2170192 bytes, stripped. I suspect 
you have not stripped yours?

Point of clarification: I was changing the .config to remove support for hardware (don't even make as a module) and 
features that I don't need in the kernel.  Was there another method being referred to with the term 'stripped' above?


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.

What does "sysctl vm.min_free_kbytes" say? Here it says "vm.min_free_kbytes = 1763"

500

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.

Hm, this sounds familiar, allthough I cant pinpoint it.

Geert responded to this in a previous mail to the group, I have to get some information back to him.


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?

I'd try with "sysctl -w vm.min_free_kbytes=500" and see if that helps. If it does, make it permanent by adding it to 
/etc/sysctl.conf

Thanks so much for this suggestion!!!  I set the value to 200, and I so far have not seen the value (via vmstat) go 
below 200, lowest observed so far has been 244.  This might be a good suggestion for m68k to make permanent?

--Lance
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