Re: Improving Performance

[Michael Schmitz <schmitz@biophys.uni-duesseldorf.de>]

Stefan,

your point regarding ST-RAM performance is well taken - in fact, it has 
been raised before. Repeatedly.

What keeps us from placing the kernel in TT--RAM is the simple fact 
that under the current memory model used by m68k, we will lose all of 
ST-RAM for use by either the kernel or user space. Traditionally, the 
memory chunk that the kernel is located in will be the first chunk 
listed in the bootinfo, and also the first one to be initialized for 
use by the kernel. The currently employed memory model does require 
memory chunks to be in ascending order. ST-RAM as second chunk violates 
that assumption. There may be a way to make use of defined portions of 
ST-RAM as IO memory, but that has not been tested so far. I need to 
look into how much effort this would take.

Switching to a different memory model will need someone to dig into the 
arcana of memory management - this ought to be possible to test on 
ARAnyM. Both Atari and Amifga stand to benefit from this, by the way. 
The port has recently procured RAM expansions for Amiga that don't work 
with the current memory model either, and need a different memory model 
for much the same reason. What we lack is someone with enough Linux and 
m68k memory management skills, apparently.

Bear in mind that disk I/O on the Falcon is bound to be slower than on 
the Amigas (IDE on the slow bus vs. SCSI, I would presume). If you're 
feeling bold, give the Falcon SCSI driver a try, but please apply all 
of the recent patches posted to linux-m68k first.

Cheers,

	Michael


Am 08.03.2014 um 06:33 schrieb Stefan Niestegge:

> Hi debian/68k people,
>
> i know, while using Aranym for running debian-68k on Atari-compatible 
> machine, it doesn't make a noticeable (if any) performance difference 
> to boot the kernel with -s option (put Kernel in ST-RAM).
>
> But if you run it on a real 680x0 machine, which in my case is a
> Falcon with 100 MHz 68060 CPU, 512MB TT-RAM (read: FAST RAM, clocked 
> at full CPU clock on a 32 bit bus) and 14MB ST-RAM (read: SLOW RAM, 
> 16MHz on a 16bit bus), there is a huge performance loss.
>
> Last weekend i attended to a computer meeting, where someone ran 
> debian-68k on his Amiga 1200 (Blizzard 1230 CPU upgrade, 50 MHz CPU 
> clock, 64MB FAST RAM (but iirc on Blizzard 1230 RAM clock is half CPU 
> clock). This machine _easily_ outperformed mine, though having much 
> lower raw power.
>
> Wouldn't it be the right way to fix the Atari-branch kernel to get
> it running from TT RAM as on the Amiga? The Amigas 2 MB Chip RAM is 
> not used by the linux kernel, only for video-RAM.
>
> If some developer lives halfway near me, i'd even lend him/her my 
> (precious) Falcon to have hardware to test.
>
> I am on my way to write a good debian-68k install walkthrough for 
> Atari Falcon, because its quite tricky to get it running.
>
> But with this poor performance, i don't know if its worth the effort.
>
>
> Any suggestions are very welcome, i have my Falcon set up on my main 
> desk and latest debian-68k is installed. Network support works nicely.
> I even compiled my favorite console IRC client on it.
>
> greetings,
> Stefan
>
>
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