S/390 Support is Now on Kernel 2.2

Alan Cox has released kernel 2.2.14pre14 (And now 15). The big news is that IBM S/390 Support is now merged into the 2.2 kernel (most of it). Currently the port features: Full SMP support, Disk, Networking & Console. More details can be found on this feature from Linux Today

Comments

Re:Why?

[davie]

The OS that runs on the S/390 supports multiple virtual machines. As I understand it, Linux will run in one or more VM partitions (?)--it will not be the primary OS.

Linux portability embarasses some companies

[RNG]

With Linux ports now ranging from PDAs to PCs to Workstations and now to Mainframes, Linux is acutally proof that you can write a portable OS without using a Mircokernel. The argument used to be that only a Microkernel based OS would be highly portable but Linux proves that this is not true. We've gone from 1 platform (IBM PCs) to lots of them (I have no clue what the current count is) with the first few being done with (virtually) no commercial backing.

Some companies out there (with deep pockets) who once claimed (or at least aimed for) portability across platforms, should be seriously embarassed by this. Linux proves that portability can be achieved under a traditional/monolithic kernel design. And while some OS purists/professors may argue about some of the finer points of this, it should be noted that Linux is here now and it works on a ton of platforms. The fact that it's free and (as far as an OS can be) cool is an added benefit, with the latter being lost on 99+% of the population ...

Re:Linux portability embarasses some companies

[um... Lucas]

Well, it still is infeasible for any company to do. Think of how many developers Linux has. Then pay them dirt cheap, say $60K/year... What's that put your payroll at?

But what a company couldn't do, a community of individuals can do, because there isn't the underlying motive of making money... Of course that's all changed now, thanks to RHAT and LNUX, but hopefully there's still enough of the original drive left that Linux will emerge unscathed.

So far as your "free" goes... we've discussed this before, but linux is only free as in money, not as in speech.... That's a discussion for another day, however.

Re:Why?

[jlnance]

From what I hear, the reason they are doing the port is that they found that mainframes make great web servers, but it is easier to port Linux to the 390 than it is to port all the programs you would want on your web server to MVS or CMS

Learn to use patch!

[Adnans]

If you like to muck with new kernels and don't really have the bandwith learn to use patches PROPERLY, it's not that hard. If not, just stick with your favourite distribution and wait for the next CD release to upgrade.

Splitting the kernel into separate architecture modules is going to be a nightmare for the kernel maintainers. They will have to spend more time maintaining and less time hacking, you don't want that do you? Besides, the archive is only 13MB bzipped2'd now. That's only like 3 full length mp3 songs! Think about that! :)

-adnans

PS. 'fraid of messing up your kernel tree with patch? Try patch with --dry-run first.

what does "mainframe" mean?

[MattMann]

What is a mainframe from the point of view of linux? What sort of changes are required to port to a mainframe, particularly to a S390? Folks talk about stuff like IO channels and VMs but what are the salient features that I don't know about?

Assuming I'm familiar with von Neuman architecures, stack machines, microprocessors, minicomputers, memory mapped memory, memory mapped devices, IO ports, interrupts, and the unix concepts of streams, char devices, block devices, etc... what don't I know about mainframes? (Please don't make me read the source :)

One thing I *do* know from using them briefly, is that IBM "terminals" (3270s? something like that) are really weird: they are not simply connected via a serial cable. They have these extra control signals that light up indicators that say "you can't type now, I'm busy" and the text editors seem to do their editing on the "screen" locally and then send the changes back when you are done. I realize this has nothing to do with the kernel, but it would seem to make the whole experience quite surreal.

Re:what does "mainframe" mean?

[Guy Harris]

What is a mainframe from the point of view of linux? What sort of changes are required to port to a mainframe, particularly to a S390? Folks talk about stuff like IO channels and VMs but what are the salient features that I don't know about?

I/O channels: at least on System/3x0, I/O is done by constructing a "channel program", which is a series of commands whose opcodes tell the channel, and the peripheral attached to it, to perform some operation (read data, write data, search a disk track for a block whose "key" has a certain value, rewind a tape, etc.) - there's also a branch instruction (Transfer in Channel) and, as I remember, some ability to do conditional skips over channel commands. The CPU just issues instructions such as "start I/O" to start a channel program; the channel program does the data transfer.

VMs: one "meta-OS" running on S/3x0 mainframes provides, to the OSes running atop it, a "virtual machine", that looks much like a real S/3x0, and whose disks might be subpartitions of the real machine's disks, whose communications controllers might be part or all of the real machine's communications controllers, whose system console might be the terminal on which the operator of that virtual machine is logged in, etc.. (VMware is somewhat like this.) Linux could run on one of those "virtual machines", and one of the other OSes for S/3x0 could run in another one, so that you can run applications for Linux and applications for, say, OS/390 on the same machine, without having to port a UNIX application from Linux to OS/390 (which has a UNIX environment - but it's not completely like the UNIX environment to which most UNIX programmers might be used, e.g. it doesn't use ASCII as its native character set, it uses IBM's EBCDIC).

Assuming I'm familiar with von Neuman architecures, stack machines, microprocessors, minicomputers, memory mapped memory, memory mapped devices, IO ports, interrupts, and the unix concepts of streams, char devices, block devices, etc... what don't I know about mainframes?

Well, IBM mainframes have a fairly conventional von Neumann-architecture instruction set (CISC, 16 32-bit general-purpose registers, variable-length instructions, memory-to-memory character/decimal arithmetic instructions, memory-to-register and register-to-register binary arithmetic instructions) with some specialized add-ons. The CPUs in them are, these days, microprocessors implementing that instruction set.

I don't know if OS/390 implements memory-mapped files, but the hardware certainly permits it - it has a fairly convention in-memory-page-table MMU.

I/O devices aren't memory-mapped, however; you tell them to do things by telling a channel to send them commands. The channel program can interrupt the CPU either to say that it's finished or, as I remember, to notify it that it's reached a certain point in the program.

The UNIX I/O model isn't what OS/3x0 has traditionally implemented, although the UNIX environment atop it implements that, and a Linux port would implement such an I/O model.

One thing I *do* know from using them briefly, is that IBM "terminals" (3270s? something like that) are really weird: they are not simply connected via a serial cable. They have these extra control signals that light up indicators that say "you can't type now, I'm busy" and the text editors seem to do their editing on the "screen" locally and then send the changes back when you are done. I realize this has nothing to do with the kernel, but it would seem to make the whole experience quite surreal.

How surreal was your experience posting your article? You presumably filled in the text in the "Comment" box, doing any editing locally, and then sent the changes to Slashdot's server when you were done by pressing the "Submit" button.

I remember, several years ago, reading some magazine in which somebody described much of the Web as "3270 for the '90's". A lot of the stuff with HTML forms and HTTP POST operations resembles the way I think 3270's work.

The instruction set and I/O architecture of S/390 is described by ESA/390 Principles of Operation. Links to that and some other manuals can be found on the Linux on the IBM ESA/390 Mainframe Architecture page.

I can see it now....

[dhms]

I can see it now... the scene: March 1, 2000, a call to IBM's Large Systems Group Order line...

IBM: Hello, IBM S/390 sales group, how may I help you?

Caller: I'd like to buy a '390 with 32 CPUs and 64GB of main memory

IBM: Would you like disks and communications with that?

Caller: Yes. I'd like 400 terabytes of redundant, channel attached DASD's, a full compliment of COMC's for 3270 and ANSI terminal devices for 500 directly connected users, LU6.2, SNA and TCP/IP networking over fiber and coax and an attached robotic tape library.

IBM: Which operating system would you like? VM/390 or Linux?

Caller: Linux, please.

IBM: No problem. We can pre-install it, or you can download it from ftp.kernel.org on the Internet.
We'll schedule overnight delivery of your system, please make sure there's someone available in your data center who can sign for the delivery...
Oh, and will you be paying for this with Mastercard, Visa, American Express or a purchase order (valid D&B required)...?

Caller: Bummer, you don't take Discover? Um... Amex, I guess. Can I get some Linux/390 t-shirts and coffee mugs with that too?
:
:

Hmmmmm.... I wonder how much power and A/C I'd have to install in the basement in order to...

Why? Why?

[Greyfox]

Because they can!

There's quite a huge Linux culture in IBM that is currently comprised mostly of techies -- very few people in management really understand or use the OS (Though they are getting caught up in the hype, so the hype does have its uses.)

IBM has accidentaly managed to hire some very sharp technical people, many of whom the corporate culture has not yet crushed the spirit out of yet, and those people might say "Gee, it'd be neat to port Linux to a S/390." Much of the cool stuff that has come out of IBM in the historical past has been initiated by single employees in the company, often working on their own time. I'm rather surprised the S/390 changes were allowed to be released, since the standard IBM contract says IBM owns anything you do in your own time and AFAIK they have not yet released any guidelines for writing open source softwre in your own time.

HAH! Mindcraft THAT, bitch!

[Greyfox]

Ok, I think this calls for a new Mindcraft test.

Lets take the biggest hardware NT runs on and the biggest hardware Linux runs on...

I guess this pretty much kills the FUD about Linux not scaling well...

History from within the Big Blue Beast

[Anonymous Coward]

Back in the summer of 1998 it slipped out in an open IBM Linux online forum that an intern in the Toronto Labs had, in his spare time, ported Linux to run under VM on a 390 mainframe. There was a lot of talk amongst us propellerheads about how good this would be for IBM to do with Linux what the marketing folks claimed we would do with OS/2 (and failed).

Then the PHB's broke into the discussion and squished it. It frightened them. I think it still does. IBM doesn't make nearly as much money on the iron as they do on the software. Make the software free and there is a lot of lost revenue. Maybe the PHB's are coming around to the fact that IBM still makes zillions on service, and it's better to be the first company to offer a unified UNIX solution cross-platform than to watch a competitor do it.

With IBM actively involved in development of everything from palm devices to big iron, Linux only makes sense for selling smart solutions to customers. So, some revenue is lost on software sales. Big deal. Increased volume via bundled solutions will make up for that.

chip info

[cabbey]

goto chips.ibm.com (their microelectronics site) and search for s390. The last link is the best.

Also check out the Blue Logic(TM) section for more one the technology that enables the G6 to reach 1600 MIPS.