------- Forwarded Message
Date: Sat, 11 May 1996 10:52:53 -0500
From: Miguel de Icaza <firstname.lastname@example.org>
cc: email@example.com, firstname.lastname@example.org
Subject: Uselinux and the Linux/SPARC port
On Jannuary the Uselinux conference will be help together with the
Usenix technical conference (http://www.usenix.org). David and I had
plans to make a technical presentation on the Linux/SPARC port. I
think Linux/SPARC is not just another port, but a port that has some
unique features not found on other ports.
The idea is to co-author this paper with those of you wanting to
help/contribute to the article.
I have assembled a list of things I think are interesting on
Linux/SPARC, I guess that before we can make a presentation on why we
find Linux/SPARC to be a unique port we will have to massage this
quite a bit. I have already mailed this one to Michael Johnson (He is
the technical session chair I think), if you want to co-author this
with David and I please, contact me (and CC the sparclinux-cvs list.
David will be very busy before leaving to SGI, so I'm doing the
coordination for this).
Sparc have 3 types of MMU -- this is easy to plug into Linux.
Sparc have Virtual Addressed Caches (VAC) and Physical caches --
these require changes to Linux kernel. With the VACs, one must be
careful to not complete flush the caches as it was being done
initially, because they damage performace quite a bit.
As an extra challenge, some MMU are buggy, MMUs are accessed in
Linux/SPARC uses pointer functions for most MMU/cache manipulation
* SunOS compatibility.
We use the model that Linus used to get OSF/1 compatibility.
(we use same constants, and same structures for the kernel,
thus no need to translate anything).
This model lets us have a userland ready early during the port and
the code is written when something fails to run properly.
Compare this to NetBSD, 4114 lines of code for Sparc code plus 2753
lines of generic emulation "libraries"; compare this to Linux: 1140
lines. We think this is the right way to future ports.
Linux emulation code is mostly related to features not found
usually in Linux (like assumption from SunOS applications on the
OS), while NetBSD's emulation code is spent on doing conversions
in/from each OS constants and data structures, so Linux does not
have a runtime performance penalty for running SunOS applications.
Sparc drivers have to support the Linux interface and the SunOS
interface to make some programs happy (X-Window), the mouse driver,
keyboard driver and frame buffer drivers provide SunOS interfaces.
The mouse and keyboard driver provide the same interface to Linux
applications as it is found on original i386 port.
* Drivers for undocumented hardware.
Getting information out of Sun is not very easy. Documentation for
some hardware came from the vendor that makes the chips (scsi and
lance drivers), sources for the NetBSD, Sprite and the Xinu
operating system were used as references at the beginning of the
port to understand the architecture.
bwtwo, cg3 and cg6 drivers were based on existing NetBSD drivers
and a generic frame buffer interface for Linux/SPARC was coded. A
driver for the cg14 has been written using only Solaris include
file for the video card and some poking at the rom letting us
emulate a lowend graphics card on it.
* Stability and performance.
During the port the use of crashme has been constantly used to avoid
the same mistakes on Sun operating system.
lmbench has been used to test the performance of the operating
system. It was not just used as a benchmarking tool, but also to
pinpoint weaknesses in the port. After a couple of weeks tunning
the port, Linux/SPARC was able to keep up against SunOS and Solaris
on the same hardware and in some cases outperforming them.
The lmbench results are more interesting than they may appear at
first sight: They do not only reflect that Linux is a great
operating system, but most sadly it reflects the fact that
corporate operating systems are sometimes bloated and slow. The
reason for bloated operating systemd may come from different
sources, as documented in the 4.3BSD book, there were 13 memory
allocators on the BSD kernel in 1986, at that point they were aware
of the problem: code is being rewritten over and over. This in my
opinion means that most kernel programmers lack a deep knowledge on
the operating system and may be writting thing that are not
(anecdote: over the past two weeks I made one remark and one
suggestion to the kernel to Linus, and even when they looked fine
to me and many people agree they are Linus quickly pointed me out
where the design flaws were in; it was related rfork, btw).
Problems encountered when porting Linux to the Sparc. Not all SMP
machines are born the same, there are some hacks required to get
SMP working on the Sparc.
[Ufinished section I will complete this section later]
* Portability and the AP+
The Linux/SPARC port is itself a relatively easy to port to non Sun
hardware. Andrew Tridgell and his hackers team in Canberra have
ported Linux/SPARC to the AP+ multiprocessor.
[ This section is still not finished ]
* Bootstraping the SPARC.
Booting the SPARC required: a) cleaning up the ext2fs to make it
aware of the endianess of the SPARC; b) the merging into the
kernel of the nfsroot allowed one of the developers to work without
a hard disk, and let people test drive Linux kernel without needing
to reformat their disks.
Jay Eastabrook's Alpha console code split was used as the second
attempt at the Linux console code. Once we had this one, we got
the same functionality of Linux/i386 on the sparc.
SILO is unique in one aspect: It is the first Linux boot loader
that uses the ext2fs library from the ext2fs tool suite by Remy
Card and Ted Tso. This is a good thing because it let us write the
boot loader in a very short time frame.
The SILO bootloader fully understands the ext2fs and thus does not
require a special boot loader installer for each kernel image that
is made available. There is still work in progress on LILO to make
it work with iso9660 cdroms and boot loading.
* The port
David Miller setup an account for the developers on vger to have
access to his CVS tree so that we could make changes directly to
the source tree without taking time from him. Simple rules were
set: test before you commit your code.
Another idea that was pushed since the beginning was to keep track
of current kernel developement. Even if this would imply that we
had to spend some time merging and fixing sparc stuff on our
kernels, it helped us to merge our tree faster and easier than the
other ports. Letting versions slip proved to be not a very good
idea, and the MkLinux people will suffer with it as did the m68k
guys some months ago.
The first attempt at a Libc port was done by porting Linux's a.out
Libc4 to the SPARC. Later a GNU libc port was attempted, but
because of the adapting nature of the kernel to the host OS for
binary compatibility, the GNU libc port was found to not be
possible at the time, we may try again as soon as some issues are
hashed out on glibc.
Currently the Linux Libc 5 is in use and ELF loading has been fixed
into the kernel. Eric Youngdale is making the elf loader less
i386-centric, and thus our patches will go in easier.
The libc5 supports shared executables and Eric's ld.so linker has
been ported to the SPARC, as well as adapting it to Linux
(originally it was written and tested on Solaris). What is amazing
is that this linker is quite portable nowadays.
RedHat and Debian are both working on Linux distributions for the
SPARC. The goal is to have the same interface on all different
architectures and in the future encourage commercial software
companies to compile with a cross compiler versions of their
software for all the available platforms of Linux.
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