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IEEE Says Multicore is Bad News For Supercomputers

Posted by timothy on from the unexpected-downsides dept.

Richard Kelleher writes "It seems the current design of multi-core processors is not good for the design of supercomputers. According to IEEE: 'Engineers at Sandia National Laboratories, in New Mexico, have simulated future high-performance computers containing the 8-core, 16-core, and 32-core microprocessors that chip makers say are the future of the industry. The results are distressing. Because of limited memory bandwidth and memory-management schemes that are poorly suited to supercomputers, the performance of these machines would level off or even decline with more cores.'"

10 of 251 comments (clear)

  1. Time for vector processing again by suso · · Score: 5, Insightful

    Sounds like its time for supercomputers to go their own way again. I'd love to see some new technologies.

    1. Re:Time for vector processing again by jellomizer · · Score: 5, Interesting

      I've always felt there was something odd about the recent trend of Super Computers using common hardware. components. They have really loss their way in super computing by just making a beefed up PC and running a version of a common OS which could handle it. Or Clustering a bunch of PC's togeter. Multi-Core technology is good for desktop systems as it is meant to run a lot of relatively small apps Rarely taking advantage of more then 1 or 2 cores. per app.In other-words it allows Multi-Tasking without a penalty. We don't use super computers that way. We use them to to perform 1 app that takes huge resources that would take hours or years on your PC and spit out results in seconds or days. Back in the early-mid 90's we had different processors for Desktop and Super Computers. Yes it was more expensive for the super computers but if you were going to pay millions of dollars for a super computer what the difference if you need to pay an additional $80,000 for more custom processors.

      --
      If something is so important that you feel the need to post it on the internet... It probably isn't that important.
    2. Re:Time for vector processing again by virtual_mps · · Score: 5, Insightful

      It's very simple. Intel & AMD spend about $6bn/year on R&D. The total supercomputing market is on the order of $35bn (out of a global IT market on the order of $1000bn) and a big chunk of that is spent on storage, people, software, etc., rather than processors. That market simply isn't large enough to support an R&D effort which will consistently outperform commodity hardware at a price people are willing to pay. Even if a company spent a huge amount of money developing a breakthrough architecture which dramatically outperformed existing hardware, the odds are that the commodity processors would catch up before that innovator recouped its development costs. Certainly they'd catch up before everyone rewrote their software to take advantage of the new architecture. The days when Seymour Cray could design a product which was cutting edge & saleable for a decade are long gone.

    3. Re:Time for vector processing again by AlpineR · · Score: 5, Insightful

      My supercomputing tasks are computation-limited. Multicores are great because each core shares memory and they save me the overhead of porting my simulations to distributed memory multiprocessor setups. I think a better summary of the study is:

      Faster computation doesn't help communication-limited tasks. Faster communication doesn't help computation-limited tasks.

    4. Re:Time for vector processing again by knails · · Score: 5, Insightful

      No, proper spelling and grammar are important for everyone, not just english majors. With computers so important, if the computer professionals cannot use the language correctly, then who will? We cannot let ignorant people degrade the quality of language and therefore remove beauty and subtle distinctions between similar words just because they're too lazy to conform to standards. If a linguist misused/ignored computing standards, would you not correct them, even though it's not their chosen field of study?

      --
      "I disapprove of what you say, but I'll defend to the death your right to say it" -Voltaire
    5. Re:Time for vector processing again by necro81 · · Score: 5, Interesting

      A related problem to the speed of memory access is the energy efficiency of it. In an IEEE Spectrum Radio piece interviewing Peter Kogge, current supercomputers can spend many times more energy shuffling bits around than operating on them. Today's computer can do a double-precision (64-bit) floating point operation using about 100 picojoules. However, it takes upwards of 30 pJ per bit to get the 128 bits of data loaded into the floating point math unit of the CPU, and then moving the 64-bit result elsewhere.

      Actual math operations consume 5-10% of a supercomputer's total power, moving data from A to B is approaching 50%. Most optimization and innovation in the past few decades has gone into compute algorithms in the CPU core, and very little has gone into memory.

    6. Re:Time for vector processing again by hey! · · Score: 5, Interesting

      It may be true that "That market simply isn't large enough to support an R&D which will consistently outperform commodity hardware at a price people are willing to pay," that's not quite tantamount to saying "there is no possible rational justification for a larger supercomputer budget." There are considerable inflection points and external factors to consider.

      The market doesn't allocate funds the way a central planner does. A central planner says, "there isn't room in this budget to add to supercomputer R&D." The way the market works is that commodity hardware vendors beat each other down until everybody is earning roughly similar normal profits. Then somebody comes a long with a set of ideas that could double the rate at which supercomputer power is increasing. If that person is credible, he is a standout investment, not just despite the fact that there is so much money being poured into commodity hardware, but because of that.

      There may also be reasons for public investment in R&D. Naturally the public has no reason to invest in commodity hardware research, but it may have reason to look at exotic computing research. Suppose that you expected to have a certain maximum practical supercomputer capability in twenty years' time. Suppose you figure that once you have that capability you could predict a hurricane's track with several times the precision you could today. It'd be quite reasonable to put a fair amount of public research funds into supercomputing in order to have the that ability in five to ten years' time.

      --
      Post may contain irony: discontinue use if experiencing mood swings, nausea or elevated blood pressure.
    7. Re:Time for vector processing again by knewter · · Score: 5, Funny

      Hey dipshit. When you mock someone's grammar, you'd sure as fuck better not mis-spell 'apostrophe'

      Idiot.

      I'll paste it a few times so you can look at your grotesque failure more:

      aprostrophe
      aprostrophe
      aprostrophe
      aprostrophe

      See how stupid that looks?

      --
      -knewter
  2. Yeah! by crhylove · · Score: 5, Funny

    Once we get to 32 or 64 core cpus that cost less than $100 (say, five years), I'd HATE to have a beowulf cluster of those!

    --
    I hold very few opinions. I hold information based on observation and fact. If you wish to disagree, please use facts.
  3. Unganged channels = already non shared lanes today by DrYak · · Score: 5, Insightful

    The issue is with a single processor that has multiple cores.
    There's no real way to split the banks for each core, so the net effect is that you have 4-32 cores sharing the same lanes for memory.

    No, sorry. That's how Phenom processor are *Already* working.

    Each physical CPU package has two 64-bit memory controllers, each controlling a separate bank of 64bits DDR-2 memory chips. (Each of the two bank in a dual channel mother board).

    Phenom have two mode of function :
    - Ganged : both memory controllers work in parallel, working as if they were a huge 128bits memory connection. That's how dual channel has worked since it was invented.
    That's good for system running few very bandwidth-hungry applications (for example : benchmarks)

    - Unganged : each memory controller work on its own. Thus you have two completely separate 64bits memory channel accessible at the same time. By correctly lying the applications in memory thanks to a NUMA-aware OS (anything better than Windows Vista), that means that two separate applications can simultaneously access each one's memory at the exact same moment, although at only half the bandwith *per process* (but still the same total of bandwidth for all processes running at the same time on a multi core chip).
    This is perfect for systems running lots of tasks in parallel, and is the default mode on most BIOSes I've seen.

    This gives a tremendous boost to heavily multi-tasked applications (a busy database server, for example), and it's what TFA's author are looking for.

    Probably that at some point in the future, Intel will follow the same trend with its QPI processors.

    Also, the future trend is to multiply the memory channels on the CPU: Intel has already planned Triple Channel DDR-3 for their high-end server Xeons (the first crop of QPI chips). AMD has announced 4 memory channels for their future 6- and 12- core chips targeting the G34 socket.

    So the net effect of Unganged Dual Channel is that today you already have 4 cores having a choice of 2 sets of memory lanes to choose among, and within 1 year, you'll have 6-to-12 cores sharing 4 sets of memory lanes.

    By the time you reach 32 cores on CPU, probably that almost each slot will have its own dedicated memory channel (probably with the help of some technology which communicates serially with fewer lines, like FB-DIMM). Or even weirder memory interfaces (who knows ? maybe DDR-6 will be able to give several simultaneous access to the same memory module).

    So, well, once again, it proves that running stupid simulations without taking into account that other technologies will improves beside the number of cores* yields stupid non realistic results.

    Shame on TFA's Author, because the trends to increase bandwith have already started. I little bit more background research would have avoided this kind of stupidity.
    But on the other hand, they would have missed the opportunity to publish an alarmist article with an eye catching title.

    --

    *: Although, yes, the number of cores you can slap inside the same package seems to be the "new megahertz" in the manufacturers' race, with some like Intel trying to increase this number faster without putting so much efforts on the rest.

    --
    "Sufficiently advanced satire is indistinguishable from reality." - [Tips: 1DrYakQDKCQ6y52z6QbnkxHXAocMZJE61o ]