The AS/400 Lessons Come Back Around With Power9 Systems
December 11, 2017 Timothy Prickett Morgan
For many years before I took the job as Systems Editor at The Register and in the years since I left that post, the joke about any new system or device was: “Yes, but can it run Crysis?” Those of us writing stories would bend a few sentences around the idea, particularly with Linux systems, which if you equipped them with the WINE Windows emulator might allow said device to indeed run that first-person shooter game that was popular from 2007 through 2013.
As we think about the new “Witherspoon” Power9 server that IBM launched last week, we can’t help but think: “Yes, but can it run IBM i?”
The answer is a subtle one, and it is that, yes, in theory, there is no reason why this very impressive hybrid CPU-GPU system cannot run IBM i, which absolutely would boot on the machine. But so much of the box, at this point in the history of the venerable line of OS/400, i5/OS, and IBM i midrange operating systems, would be absolutely useless to those platforms that there is not much point to it. But, as is often the case with supercomputing, when you look at the machinery in use today, you are looking at what could end up being the future of enterprise computing sometime in the future. This is something that I talked about in The Supercomputer At The Heart Of The Power Systems Revival a year ago, and then elaborated on further, with what I hope was some encouragement, in how this supercomputer, stuffed to the gills with CPU and GPU compute, might make a new generation of IBM i platforms. (See The Cognitive Systems/500 2018 Edition, which we published in June, for more on that.)
The point now is that IBM has in fact brought its first Power9-based system to market, and this “Witherspoon” system, which is called the AC922, short for Accelerated Computing, in the IBM catalog is the foundation of Big Blue’s resurgence, if there is to be any, in the Power architecture in the datacenter. The AC922 is now the heart of its Cognitive Systems division. If this machine succeeds in gaining market share against systems and clusters using Intel’s Xeon or Xeon Phi processors or hybrid boxes that mix Xeons and Tesla GPU accelerators from Nvidia – for both traditional HPC simulation and modeling workloads but also for visualization, machine learning, and accelerated database workloads that are being goosed by GPUs – then IBM’s commitment to Power will increase as it makes money, and that will make it easier to justify continuing investment by end user customers in more traditional Power Systems iron that is not so heavily in need of acceleration outside of the CPU and memory.
The Witherspoon system is the third of a line of Power Systems LC machines aimed at HPC and AI workloads, the other two being the “Firestone” Power8 Power S822LC machine with four “Kepler” class GPU accelerators from 2015, followed by the “Minsky” Power S822LC for HPC that was announced last September with the Power8+ processors and its integrated NVLink interconnect to lash the GPUs more tightly to the CPUs than could be done over the PCI-Express bus in the system alone. The Firestone machines were no better than X86 alternatives, and had some strikes against them because their Power8 processors ran hotter than Xeon chips and they did not have any advantages when it came to I/O. With the Minksy machines, IBM got the first 16 Gb/sec NVLink 1.0 ports onto processors, which allowed for fast transport of data between the CPUs and memory sharing between the GPUs that were linked in a 2D mesh to each other. With the Witherspoon machines, the GPUs are cross coupled using faster 25 Gb/sec NVLink lanes (with multiple lanes bundled up for extra bandwidth) and also linked to the Power9 processors using those fatter NVLink 2.0 pipes. But here is the magic: The memory across the CPUs and the GPUs is coherent, meaning any device can directly address any point in either the CPU or GPU memories. This is a kind of asymmetric multiprocessing that made the original AS/400 such a genius device, with intelligent I/O processors – remember IOPs? – having the ability to address anything in the combined single-level storage across the main memory and disk storage.
IBM Rochester has seen this movie before, only this time, the IOPs (GPUs and FPGAs) are more powerful than the central processors (the Power9 chip, in this case). And if you want to be fair about it, even with the IOPs in the past with the AS/400, the aggregate raw processing power was probably a lot larger across the adjunct processors in the system than in the central processor. My point is this: The style of asymmetric processing that was embodied in AS/400s was an important innovation back in 1988, and while the consolidation of the AS/400 and RS/6000 lines that began way back in the middle 1990s and that was completed in the middle 2000s moved away from all of this, the limits of Moore’s Law, like the limits of bipolar and then CMOS CISC processors that lead to RISC designs and the move away from using a cluster of processors of different types to share the processing, is leading IBM back down the asymmetric system road once again.
Maybe they should have called it the Asymmetric System/500 instead of the AC922?
In any event, if you want to get all of the feeds and speeds of the new Witherspoon system, I have gone through it in quite a bit of detail at The Next Platform, my other day job. I don’t see the point in repeating the whole thing again here. That story, called Power9 To The People, goes over the basic feeds of the AC922 system and I will be working on a follow-on that covers the speeds this week.
For the IBM i crowd, I think the advent of the Witherspoon system is cause for hope in the resurgence of the Power Systems line at IBM. Big Blue has successfully re-entered the market with a serious processor with open (well, licensable) interconnects, and popular accelerators that creates a very compelling and, at first glance, a reasonably affordable hybrid computing platform that can be shaped to fit myriad modern workloads. It is a new foundation for the business, and this hardware platform will evolve and could be the foundation of a new kind of souped up, inclusive IBM i platform with a slew of very sophisticated, modern analytics that gives midrange companies the kind of capabilities that the hyperscalers have invented.
We encourage Big Blue to Think Big for its midrange customers, not just large enterprises who want to act like Google, and we hope that the company has such high aspirations. We do.