SGI And /Massive/ Linux Machine

Thanks to some of the folks from SGI for sending us some information about their latest project. Pretty interesting project -- the largest configuration has 10 PCI busses (busi?) with 24 scsi controllers and 10 disks. And wait'll you see the rest of the stats.

Hi all,

Just thought I would send out a note outlining the state of the mips64 port. Ralf, Ulf and I have been actively working past few months to bring up Linux on the SGI ccNUMA machines.

The executive summary: we have achieved multiuser boot on o200 and o2000s. The largest configuration is a 32p, 16node machine (only approx 4G worth of memory was populated over the 16 nodes, the system can take 4G * 16 node worth of memory). This machine has 10 PCI busses, with 24 scsi controllers and 10 disks. (Sample output is at

OSS SGI

If you are interested in the system architecture and details of the port, read on. The o2000s use R10000 series of MIPS processors. Each machine is comprised of modules, each module has 4 node boards with max 2 cpus and 4G memory on each node, and IO boards and routers. In a module, the two alternate node boards are each connected to a XBOW. Each XBOW possibly is connected on the other side to a number of PCI busses, which is what the IO boards connect to. Apart from this, there are routers in the system that provide connection paths between all memory to all cpus, to create a true CC-NUMA architecture.

On the software side, we are still struggling with compiler and binutils issues. The kernel itself is 64 bits, created by cross compiling on an ia32 box. We have not attempted 64 bit user program compilation or execution. The root disk is currently very close to the MIPS/Indy root disks. The architecture specific code uses the CONFIG_DISCONTIGMEM code to support memory on all nodes. The architecture specific NUMA features currently are: 1. replicate the kernel text on all nodes, so that no one node becomes a memory hot spot (unfortunately, the kernel data has to reside on only one node). 2. replicate low level excpetion handler code on all nodes. The architecture code also turns on CONFIG_NUMA to take advantage of node-local page allocations. (A CONFIG_NUMA patch that I have been submitting to Linus was put into the kernel in test6-pre1). For more information on NUMA and ongoing work, refer to

this document

The purpose of doing this port is to boot Linux on bigger systems that we have, in order to do cpu/memory scalability studies. This also lets us do NUMA performance work in the future. Another advantage is to be able to leverage this work on the upcoming SGI CC-NUMA Itanium boxes, which will be an SGI supported product. Initial results from scalability studies using mips64 is documented at

The OSS SGI site.

Kanoj

Comments

Someone...

[enneff]

...give this guy a fat ip pipe and a gnutella node! This machine has 10 PCI busses, with 24 scsi controllers and 10 disks. !!!!!

nf

Re:Why?

[stuce]

SGI has already commited to producing huge
NUMA servers based off the Itanium processors.
Porting IRIX to this new architecture will be
a huge undertaking as it has been tied to the
MIPS architecture forever. Linux on the other
hand ports quite easily. SGI is doing research
as to what it would take to get Linux to
run well on massive boxes like these.

If linux can cut the mustard there will be
no need to port IRIX and that will save SGI
one huge headache.

A perfect machine for render land and other uses

[tolldog]

This is a great machine for rendering or any other application that is both CPU and memory bound.

Some jobs do not parrallel well, such as individual frame rendering. With 24 boxes, the 5 + minute overhead of loading the scene file plus the memory spent on loading the textures and the geometry would be done on each machine, costing you 24x's the overhead of doing it on one machine. Trying to do this with a "quasi" shared memory system would kill the network. But would remove that hidious overhead.
Doing this on a NUMA box fixes all of those problems. The memory is shared. The procs all look like one machine. The system runs smooth and well.

This is why SGI is still in the large graphics server environment. People want individual frames done fast.

The benifit of this being a linux box and not Irix....
I, a huge linux vs. irix advocate, strugle to see why this would be good. Most of the apps that I would use are built for Irix first and then Linux (like Maya's renderer). I can see where others might have custom apps to use this, but the code would probably port to Irix just as easily as it would to Linux on the MIPS.

It is a step in the right direction, IA64 NUMA boxes running linux. The ultimate in render farm machines.

Discover...

[pointwood]

> Discovered 32 cpus on 16 nodes

Why does my kernel not discover something like that? ;-)

Re:Why?

[NumberCruncher]

The commercial benefit is several-fold:

• Large memory/IO capable systems running a standard OS, with standard tools, and a well known ABI/API
• Highly scalable and reconfigurable modular computing. If you need more power, add more C-Bricks. If you need more IO, add more P or X bricks.
• Large application base: Linux has captured mindshare of devolopers. Applications are being ported at a furious rate. It is becoming the dominant platform for software development (over Solaris and other similar Unices).

There are many other reasons as well, but frankly this type of machine is what many people have been waiting for. The total cost of ownership of all those Sun machines is far larger than of this machine. The performance of this machine is significantly ahead of your typical Sun machine.

One of the nicest features of this machine is that you can reconfigure it with a reboot (no recabling) to come up as a single large machine or as multiple medium machines, or many single machines. You can configure the computer to your needs, not shoehorn the problem to fit within a solaris boxes limitations. And unlike on other OSes, the partitioning actually works here.

Re:I see why they ditched Cray

[stripes]

You can see why they ditched Crey Supercomputers.

Um, their Cray division did alot of the work for the O2000! In fact at release the >64CPU configs were only avail from cray. Oh, and the frame to frame comm channel? It's named the "CrayLink".

Nice machines though, even if a bit long in the tooth (the O2000 is fourish years old, the O3000's should be announced anytime now, go look at comp.arch)

If you want economical, "Beowulf" clusters are the way to go now a days.

Sure, if you need very little communication between machines Beowulf is great, and the O2000's expensave comms (the xbow and craylink) are waisted. If you need a lot of comm, but not a lot of com a O2000 is great. If you need a lot-lot of comm maybe you are out of luck until the O3000, HP SuperDome, or IBM Power5 show up.

Quick MP break down:

• NORMA - NO Remote Memory Access - Beowulf is a NORMA, to get at memory on other systems you need to make OS calls, or at least use really expensave mmap'ed (NFS) files (i.e. non local memory costs 1000x more then local memory to access).
• NUMA - Non-Uniform Memory Access - remote memory costs maybe 10x more then local memory access, and caching has to be handled specally (i.e. each system has to know when to flush it's cache "magically"). Very few examples, some IBM research machines do this.
• ccNUMA - Cache Coherent Non-Uniform Memory Access. Remote memory access costs maybe 10x local, but the cache's work. Most large multip-processor machines work this way. The O2000, the Sun E10000. The E10000 has much less then a 10x penality for remote memory, but local memory costs more then the O2000's local accesses. On both the OS can move pages from CPU board to CPU board depending on access. The E10000 comes closest to giving the impresion that it is a UMA machine (and the O2000 isn't bad at it)
• UMA - Uniform Memory Access. There is no remote memory, or no penality for accessing it. A tipical multiprocessor PC works this way. Tipically easy to build for small numbers of CPUs, incresingly impossable for larger numbers (or useless - you could make a UMA for 1024 CPUs by having extra shitty memory access times, but there is no known way to make one with good access times, even if you had a literally unlimited budget!).

  A NORMA (or better) is great for raytracing, crypto cracking, and the like. A UMA is great for N-body simulation (with large N). I wouldn't want to track the flow of air molicules over a wing with a Beowulf, but I wouldn't want to pay for a ccNUMA if I was "just" running PR-Renderman.