Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!samsung!uunet!mcsun!hp4nl!phigate!philica!adrie
From: adrie@philica.ica.philips.nl (Adrie Koolen)
Newsgroups: comp.os.minix
Subject: Re: Patches to PC MINIX and splitting this group
Message-ID: <786@philica.ica.philips.nl>
Date: 28 Mar 91 07:42:35 GMT
References: <4177@rwthinf.UUCP>
Reply-To: adrie@beitel.ica.philips.nl (Adrie Koolen)
Organization: Philips TDS, Innovation Centre Aachen
Lines: 29

In article <4177@rwthinf.UUCP> u31b3hs@cip-s02.informatik.rwth-aachen.de (Michael Haardt) writes:
>Has anyone tried to increase the number of disk buffers in standard PC
>MINIX?  Does it give reasonable speed improvements?

On my SparcStation, I use a diskbuffer of 1536 blocks (1.5MB). When performing
a make, this speeds things up quite a bit (Minix-Sparc uses the GNU C compiler)!

>I heard some rumours about bad performance of serial lines in PC MINIX.
>It's not true at all.  One of my terminals uses 19200 baud.  I displayed
>my german dictionary on it which results in more than 1700 characters
>per second (7 data bits, one parity bit, one start and one stop bit)
>equals more than 17000 baud *effective* transfer rate.  Sounds like good
>performance to me.  These values are measured on a 386 machine with the
>provided assembler drivers.

For speedy RS232 performance, you need at least two things: a reasonable
efficient RS232 driver and efficient task switching routines. Every time
the serial controller wants to send (or has received) a byte, it issues
an interrupt and the the currently running task has to be interrupted.
This means saving the processor state and performing some administration.
On a PC, these thing can (and will) be done relatively fast. On a Sparc-
Station it's somewhat slower, the Sparc processor has 120 32-bit general
purpose registers and also 32 floating point registers have to be saved
when the interrupted process uses them. Still on a 20MHz SparcStation, I
just measured a throughput of 1840 bytes per second at 19200 baud and the
CPU isn't even half used.

Adrie Koolen (adrie@ica.philips.nl)
Philips Innovation Centre Aachen