More power efficient deep learning through IBM and PCM

Read an article today from MIT Technical Review (TR) (AI could get 100 times more efficient with IBM’s new artificial synapses). Discussing the power efficiency of a new analog approach to neural nets and deep learning.

We have talked about IBM’s TrueNorth and Synapse neuromorphic devices  and PCM neural nets before (see: Parts 1, 2, 3, & 4).

The paper in Nature (Equivalent accuracy accelerated neural training using analogue memory ) referred to by the TR article is behind a pay wall. However, another ArsTechnica (Ars) article (Training a neural network in phase change memory beats GPUs) on the new research was a bit more informative.

Both articles discuss a new analog approach, using phase change memory (PCM) which has significant power/training efficiency when compared to today’s standard GPU AI processor. Both the TR and Ars papers report on IBM developments simulating a new (PCM based) neuromorphic device that reduces training  power consumption AND training time by a factor of 100.   But the Nature paper abstract says it reduces both power consumption and computational space (computations per sq mm) by a factor of 100, not exactly the same.

Why PCM

PCM is a nonvolatile memory technology (see part 4 above for more info) that uses electronically induced phase changes in a material to establish a 1’s or 0’s state for a PCM bit.

However, another advantage of PCM is that it also can take on a state between 0 and 1. This is bad for data memory/storage but good for neural nets.

For a PCM based neural net you could have a layer of PCM (neuron) structures and standard wiring that wires all the PCM neurons to the next layer down, for however many layers required for your neural net. The PCM value would indicate the strength of the connection between neurons (synapses).

But, the problem with a PCM neural net is that PCM states don’t provide enough graduations of values between 0 and 1 to fully map today’s neural net weights.

IBM’s latest design has two different tiers of neural nets

According to Ars article, IBM’s latest design has a two tier approach to using PCM in its neural net. The first, top tier uses a PCM structure and the second lower tier uses a more traditional, silicon based structure and together they implement the neural net.

The Ars article speaks of the new two tier design as providing two digit resolution for the weight between  neuron. The structure implemented in PCM determines the higher order digit and the more traditional, silicon based, neural net segment determines the lower order digit in the two digit neural net weight.

With this approach, training occurs mostly in the more traditional, silicon layer neural net, but every 100 or so training events (epochs),  information is used to modify the PCM structure as well. In this fashion, the PCM-silicon neural net is fine tuned using 1 out of 100 or so training events to correct the PCM layer and the other 99 or so training events to modify the silicon layer.

In addition, the silicon layer is apparently implemented in silicon to mimic the PCM layer, using capacitors and transistors.

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I wonder why not just use two tiers of PCM to do the same thing but it’s possible that training the silicon layer is more power efficient, speedy or both than the PCM layer.

The TR and Ars articles seem to make a point of saying this is analogue computing. And I would guess because the PCM and the silicon layer can take on many values between 0 and 1 that means it’s not digital.

Much of the article is based on combined hardware (built using 90nm technology) and software simulations of the new PCM-silicon neuromorphic device. However, simulations like this are a standard step in ASIC design process, and if successful, we would expect an chip to emerge from foundry within 6-12 months from now.

The Nature paper’s abstract indicated that they simulated the device using standard (MNIST, MNIST-backrand, CIFAR-10 and CIFAR-100) training datasets for handwritten digit recognition and color image classification/recognition. The new device was able to approach within 1% accuracy of software trained neural net with 1% the power and (when updated to latest foundry technologies) in 1% the space.

Furthermore, the abstract said that the current device supports ~205K synapses. The previous generation, IBM TrueNorth (see part 2 above) had the “equivalent of 1M neurons” and their earlier IBM SYNAPSE (see part 1 above) chip had “256K programable synapses” and 256 computational elements. But I believe both of those were single tier devices.

I’d also be very interested in whether the neuromorphic device is compatible with and could be programmed with PyTorch or TensorFlow but I didn’t see any information on how the devices were programmed.

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Photo Credit(s): neuron by mararie 

3D CrossPoint graphic, taken from Intel-Micron session at FMS16

brain-neurons by Fotis Bobolas

IBM’s next generation, TrueNorth neuromorphic chip

Ok, I admit it, besides being a storage nut I also have an enduring interest in AI. And as the technology of more sophisticated neuromorphic chips starts to emerge it seems to me to herald a whole new class of AI capabilities coming online. I suppose it’s both a bit frightening as well as exciting which is why it interests me so.

IBM announced a new version of their neuromorphic chip line, called TrueNorth with +5B transistors and the equivalent of ~1M neurons. There were a number of articles on this yesterday but the one I found most interesting was in MIT Technical Review, IBM’s new brainlike chip processes data the way your brain does, (based on a Journal Science article requires login, A million spiking neuron integrated circuit with a scaleable communications network and interface).  We discussed an earlier generation of their SyNAPSE chip in a previous post (see my IBM research introduces SyNAPSE chip post).

How does TrueNorth compare to the previous chip?

The previous generation SyNAPSE chip had a multi-mode approach which used  65K “learning synapses” together with ~256K “programming synapses”. Their current generation, TrueNorth chip has 256M “configurable synapses” and 1M “programmable spiking neurons”.  So the current chip has quadrupled the previous chips “programmable synapses” and multiplied the “configurable synapses” by a factor of a 1000.

Not sure why the configurable synapses went up so high but it could be an aspect of connectivity, something akin to what happens to a “complete graph” which has a direct edge connection to every node in the graph. In a complete graph if you have N nodes then the number of edges is given as [N*(N-1)]/2, which for 1M nodes would be ~500M edges. So it must not be a complete graph, but it’s “close to complete” with 1/2 the number of edges.

Analog vs. Digital?

When last I talked with IBM on their earlier version chip I wondered why they used digital logic to create it rather than analog. They said to be able to better follow along the technology curve of normal chip electronics digital was the way to go.

It seemed to me at the time that if you really  wanted to simulate a brains neural processing then you would want to use an analog approach and this should use much less power. I wrote a couple of posts on the subject, one of which was on MIT’s analog neuromorphic chip (see my MIT builds analog neuromorphic chip post) and the other was on why analog made more sense than digital technology for neuromorphic computation (see my Analog neural simulation or Digital neuromorphic computing vs. AI post).

The funny thing is that IBM’s TrueNorth chip uses a lot less power (1000X, milliwatts vs watts) than normal CMOS chips in e use today. Not sure why this would be the case with digital logic but if this is true maybe there’s more of a potential to utilize these sorts of chips in wider applications beyond just traditional AI domains.

How do you program it?

I would really like to get a deeper look at the specs for TrueNorth and its programming model.  But there was a conference last year where IBM presented three technical papers on TrueNorth architecture and programming capabilities (see MIT Technical Report: IBM scientists show blueprints for brain like computing).

Apparently the 1M programming spike neurons are organized into blocks of 256 neurons each (with a prodigious amount of “configurable” synapses as well). These seem equivalent to what I would call a computational unit. One programs these blockss with “corelets” which map out the neural activity that the 256-neuron blocks can perform. Also these corelets “programs” can be linked together or one be subsumed within another sort of like subroutines.  IBM as of last year had a library of 150 corelets which do stuff like detect visual artifacts, motion in a visual image, detect color, etc.

Scale-out neuromorphic chips?

The abstract of the Journal Science paper talked specifically about a communications network interface that allows the TrueNorth chips to be “tiled in two dimensions” to some arbitrary size. So it is apparent that with the TrueNorth design, IBM has somehow extended a within chip block interface that allows corelets to call one another, to go off chip as well. With this capability they have created a scale-out model with the TrueNorth chip.

Unclear why they felt it had to go only two dimensional rather than three but, it seems to mimic the sort of cortex layer connections we have in our brains today. But even with only two dimensional scaling there are all sorts of interesting topologies that are possible.

There doesn’t appear to be any theoretical limit to the number of chips that can be connected in this fashion but I would suppose they would all need to be on a single board or at least “close” together because there’s some sort of time frame that couldn’t be exceeded for propagation delay, i.e., the time it takes for a spike to transverse from one chip to the farthest chip in the chain couldn’t exceed say 10msec. or so.

So how close are we to brain level computations?

In one of my previous post I reported Wikipedia stating that  a typical brain has 86B neurons with between 100M and 500M synapses. I was able to find the 86B number reference today but couldn’t find the 100M to 500M synapses quote again.  However, if these numbers are close to the truth, the ratio between human neurons and synapses is much less in a human brain than in the TrueNorth chip. And TrueNorth would need about 86,000 chips connected together to match the neuronal computation of a human brain.

I suppose the excess synapses in the TrueNorth chip is due to the fact that electronic connection have to be fixed in place for a neuron to neuron connection to exist. Whereas in the brain, we can always grow synapse connections as needed. Also, I read somewhere (can’t remember where) that a human brain at birth has a lot more synapse connections than an adult brain and that part of the learning process that goes on during early life is to trim excess synapses down to something that is more manageable or at least needed.

So to conclude, we (or at least IBM) seem to be making good strides in coming up with a neuromorphic computational model and physical hardware, but we are still six or seven generations away from a human brain’s capabilities (assuming a 1000 of these chips could be connected together into one “brain”).  If a neuromorphic chip generation takes ~2 years then we should be getting pretty close to human levels of computation by 2028 or so.

The Tech Review article said that the 5B transistors on TrueNorth are more transistors than any other chip that IBM has produced. So they seem to be at current technology capabilities with this chip design (which is probably proof that their selection of digital logic was a wise decision).

Let’s just hope it doesn’t take it 18 years of programming/education to attain college level understanding…

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Photo Credit(s): New 20x [view of mouse cortex] by Robert Cudmore

How has IBM research changed?

20111207-204420.jpg
IBM Neuromorphic Chip (from Wired story)

What does Watson, Neuromorphic chips and race track memory have in common. They have all emerged out of IBM research labs.

I have been wondering for some time now how it is that a company known for it’s cutting edge research but lack of product breakthrough has transformed itself into an innovation machine.

There has been a sea change in the research at IBM that is behind the recent productization of tecnology.

Talking the past couple of days with various IBMers at STGs Smarter Computing Forum, I have formulate a preliminary hypothesis.

At first I heard that there was a change in the way research is reviewed for product potential. Nowadays, it almost takes a business case for research projects to be approved and funded. And the business case needs to contain a plan as to how it will eventually reach profitability for any project.

In the past it was often said that IBM invented a lot of technology but productized only a little of it. Much of their technology would emerge in other peoples products and IBM would not recieve anything for their efforts (other than some belated recognition for their research contribution).

Nowadays, its more likely that research not productized by IBM is at least licensed from them after they have patented the crucial technologies that underpin the advance. But it’s just as likely if it has something to do with IT, the project will end up as a product.

One executive at STG sees three phases to IBM research spanning the last 50 years or so.

Phase I The ivory tower:

IBM research during the Ivory Tower Era looked a lot like research universities but without the tenure of true professorships. Much of the research of this era was in materials and pure mathematics.

I suppose one example of this period was Mandlebrot and fractals. It probably had a lot of applications but little of them ended up in IBM products and mostly it advanced the theory and practice of pure mathematics/systems science.

Such research had little to do with the problems of IT or IBM’s customers. The fact that it created pretty pictures and a way of seeing nature in a different light was an advance to mankind but it didn’t have much if any of an impact to IBM’s bottom line.

Phase II Joint project teams

In IBM research’s phase II, the decision process on which research to move forward on now had people from not just IBM research but also product division people. At least now there could be a discussion across IBM’s various divisions on how the technology could enhance customer outcomes. I am certain profitability wasn’t often discussed but at least it was no longer purposefully ignored.

I suppose over time these discussions became more grounded in fact and business cases rather than just the belief in the value of the research for research sake. Technological roadmaps and projects were now looked at from how well they could impact customer outcomes and how such technology enabled new products and solutions to come to market.

Phase III Researchers and product people intermingle

The final step in IBM transformation of research involved the human element. People started moving around.

Researchers were assigned to the field and to product groups and product people were brought into the research organization. By doing this, ideas could cross fertilize, applications could be envisioned and the last finishing touches needed by new technology could be envisioned, funded and implemented. This probably led to the most productive transition of researchers into product developers.

On the flip side when researchers returned back from their multi-year product/field assignments they brought a new found appreciation of problems encountered in the real world. That combined with their in depth understanding of where technology could go helped show the path that could take research projects into new more fruitful (at least to IBM customers) arenas. This movement of people provided the final piece in grounding research in areas that could solve customer problems.

In the end, many research projects at IBM may fail but if they succeed they have the potential to make change IT as we know it.

I heard today that there were 700 to 800 projects in IBM research today if any of them have the potential we see in the products shown today like Watson in Healthcare and Neuromorphic chips, exciting times are ahead.

IBM research introduces SyNAPSE chip

IBM with the help of a Columbia, Cornell, University of Wisconsin (Madison) and University of California creates the first generation of neuromorphic chips (press release and video) which mimics the human brain’s computational architecture implemented via silicon.  The chip is a result of Project SyNAPSE (standing for Systems of Neuromorphic Adaptive Plastic Scalable Electronics)

Hardware emulating wetware

Apparently the chip supports two cores one with 65K “learning” synapses and the other with ~256K “programmable” synapses.  Not really sure from reading the press release but it seems each core contains 256 neuronal computational elements.

Wikimedia commons (481px-Chemical_synapse_schema_cropped)
Wikimedia commons (481px-Chemical_synapse_schema_cropped)

In contrast, the human brains contains between 100M and 500M synapses (wikipedia) and has ~85 billion neurons (wikipedia). Typical human neurons have 1000s of synapses.

IBM’s goal is to have a trillion neuron processing engine with 100 trillion synapses occupy a 2-liter volume (about the size of the brain) and consuming less than one kilowat of power (about 500X the brains power consumption).

I want one.

IBM is calling such a system built out of neuromorphic chips a cognitive computing system.

What do with the system

The IBM research team has demonstrated some typical AI applications such as simple navigation, machine vision, pattern recognition, associative memory and classification applications with the chip.

Given my history with von Neuman computing it’s kind of hard for me to envision how synapses represent “programming” in the brain.  Nonetheless, wikipedia defines a synapse as a connection between any two nuerons which can take two forms electrical or chemical. A chemical synapse (wikipedia), can have different levels of strength, plasticity, and receptivity.  Sounds like this might be where the programmability lies.

Just what the “learning” synapses do, how they relate to the programmatical synapses and how they do it is another question entirely.

Stay tuned, a new, non-von Neuman computing architecture was born today.  Two questions to ponder

  1. I wonder if they will still call it artificial intelligence?
  2. Are we any closer to the Singularity now?

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