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Android processor shines light on dark silicon

8/24/2010 04:33 AM EDT
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asolomatnikov943
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re: Android processor shines light on dark silicon
asolomatnikov943   8/24/2010 5:26:21 AM
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Amazing - come up with new fancy names for a few well known things and EETimes will write an article about you. Relabel low activity factor to "dark silicon", hardware accelerators to "conservation cores" - and here it is.

Dave.Dykstra
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re: Android processor shines light on dark silicon
Dave.Dykstra   8/24/2010 6:20:15 AM
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sols comments are right to the point. However, it looks like the main issue here is to resolve the problem by somehow improving the areas that are utilized. I would more expect researchers at an esteemed institution such as UCSD to be looking for ways to make those "dark silicon" areas usable. At least they seem to have come up with a way to improve the situation, but that should not be the accepted norm.

munggnum
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munggnum   8/24/2010 6:36:41 AM
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Sols sounds a bit jaded. I attended this talk, and it seemed reasonable to me. Dark Silicon was a term coined by ARM CTO Mike Muller back in 2009. The talk has some good data about where dark silicon is coming from and how bad it's going to get -- very bad. The technical idea is to use the dark silicon area to attack the problem that caused the dark silicon problem in the first place -- power. The "accelerators" that they propose seem different than conventional accelerators in that they are automatically generated and play nice with the memory system, and in that they are intended to reduce power consumption, not necessarily to increase performance. This is probably why they use the term conservation core as opposed to accelerator. In the article, there is some mention about issues with putting the MIPS core in a low power state while the accelerators are running, but that seems to me to be fairly easy to address through power-gating cells.

asolomatnikov943
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re: Android processor shines light on dark silicon
asolomatnikov943   8/24/2010 7:01:48 AM
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I guess I have to explain basic design tradeoff: if performance is improved (or accelerated if you wish), then clock frequency and voltage can be dropped reducing energy/power. So acceleration/conservation are 2 sides of the same coin. Regarding the novelty - there is already commercial tool at least several years in the market, which automatically generate ISA extensions or accelerators. Many technical papers were published on this topic, e.g.: Automatic generation of application specific processors International Conference on Compilers, Architecture and Synthesis for Embedded Systems, Pages: 137 - 147, 2003

munggnum
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munggnum   8/24/2010 7:22:30 AM
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Sols, clearly you have some good insights, but the devil is in the details. Voltage scaling to save power is losing its effectiveness in current and future technologies because of threshold scaling limitations and insufficient Vdd overdrive. The AutoTIE work you mention, while very good, targets a much easier class of code, and does not report results on power reduction.

rick merritt
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rick merritt   8/24/2010 1:49:23 PM
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Indeed "dark silicon" and "utilization wall" are buzzwords. But the real juice here is that hardware accelerators are getting to the level of specific application workloads--and a group of college students can craft the design tools to generate them.

garydpdx
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garydpdx   8/24/2010 8:50:30 PM
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The innovation that I see is not in the homebrew design tools which carried out high level synthesis (HLS) but the idea of taking small pieces of Android OS middleware and accelerating each of them as small pieces of hardware. The small pieces add up, covering the available dark silicon (or some of what would have been dark). Most C-to-hardware translation has focused on large pieces of C code (e.g., Impulse C) or compiled binaries (e.g., Binachip) to transform into a significant IP block on a FPGA or ASIC.

Code Monkey
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Code Monkey   8/24/2010 8:40:59 PM
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This sounds a little like the sea-of-cores work Chuck Moore has been doing at GreenArrays. I didn't know about the "utilization wall" but it's another boost for async sea of cores, wierd as they are.

KB3001
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KB3001   8/25/2010 6:41:36 PM
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As sols said, this kind of effort existed before, the real question for me is how generalisable is this work? I mean if you constrain yourself to a specific application, all sorts of optimisations are possible, but could the results of these optimisations e.g. application-specific cores, be harnessed for a wider range of applications, or is it a recurring investment we have to make? The key is to strike the right granularity, and produce a fully operational system. As the article states, work on coordinating the MIPS processor operations with the acceleration cores' (as well as the operations of these) has yet to be done. What would be the resulting overheads i.e. in terms of area, speed, power? The devil is indeed in the details.

goafrit
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re: Android processor shines light on dark silicon
goafrit   8/26/2010 12:45:21 AM
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I seem to miss the innovation here. Are you telling me that this is new? For me, it is just the nomenclature that changed.

martinm_de
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re: Android processor shines light on dark silicon
martinm_de   8/28/2010 1:41:45 PM
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I guess dark silicon means a piece of circuitry which is powered off (disconnected from vdd) using a high threshold PMOS transistor to reduce the leakage current. This exists for 10 years now. Doing this on operating system level is very complicated - understandably - since operating systems do not have dedicated functions like FFT, Viterbi decoder , CDMA demodulator etc. Operating systems probably need sorting, searching in lookup tables etc. THe coding style of an OS would have to vary a lot when using hardware-based functions which have to be powered on a few clock cycles before they can be used: instead of calling a function, you would have to load data into a bufer, turn on the needed function, wait until it says 'I am ready' andthen fetch the result. These functions, coded into hardware, should be hardware independent like a good C library which is portable between different procesor sand different OSes. Sounds like a logistic nightmare.

munggnum
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re: Android processor shines light on dark silicon
munggnum   8/28/2010 4:16:26 PM
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It's interesting; some folks are having trouble seeing the forrest for the trees. UCSD is saying "mobile applications processors should be composed out of hundreds of specialized cores that can suck energy out of relatively small parts of the system but collectively attain 8x energy savings." Then they show how such a system would be constructed. They have reasonable solutions to many of the problems that have been listed above. This is definitely new. For those who are actually interested in understanding the details, they can read the actual papers off of the authors' website: http://greendroid.ucsd.edu/

Neon God
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re: Android processor shines light on dark silicon
Neon God   8/28/2010 4:16:59 PM
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Question for anyone here. If we're heading for the ever more serious "dark silicon" challenges that munggnum speaks of, is that apt to be good for the leading semi IP developers (because it will lead to more ways for them to differentiate their product) or bad for them (because it will make the way forward grind to a halt as research starts bumping up against theoretical limits)? I'm thinking, in particular, with regard to Ceva, the leader in DSP cores, though I'd be interested in anyone's thought as to the likely effects of the so-called "dark silicon" issue on the semi IP business as a whole. Thanks in advance.

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