TOP3 blunders

By: ? (, September 27, 2009 8:33 am
Room: Moderated Discussions
someone ( on 9/27/09 wrote:
>Jouni Osmala ( on 9/26/09 wrote:
>>There is multiple order of magnitude difference between special purpose hardware
>>and software configurable in terms of perf/power generally. The big difference,
>>is that instead of spending huge number of transistors selecting operations, and
>>decoding instructions looking dependencies, you just have small units that just do the work.
>>Byte addition costs~200 transistors 32bit addition ~1000 transistors. and & or are 4 transistors per bit.
>>Shift by constant known before are almost free.
>>For multiplier it approximately takes an adder sized of first operand per bit of second operand.
>This may be helpful for perspective:
>Interesting comparison of MPU energy cost today
>64 bit multiply-add - 200 pJ
>read 64 bits from cache - 800 pJ
>move 64 bits across chip - 2000 pJ
>execute an instruction - 7500 pJ
>read 64 bits from DRAM - 12000 pJ

>Notice it costs 15X more energy to go to memory than
>read data from cache. The execution of a multiply-
>add instruction burns 97% of the energy in overhead
>and 3% in the arithmetic circuits.
>Also notice it is more energy efficient to redundantly
>perform 9 separate multiply-add operations in different
>locations across a chip than do it once in one location
>and broadcast the result across the chip! (presuming
>the operands were already widely distributed).
>from IDF paper TCIS001, slide 19

Thanks, nice paper.

However (there is always another "however" with me), notice that it says it is 12000 pJ per *operation*, not per *clock*. Since reading 64 bits from DRAM takes ~100 cycles, isn't it only ~120 pJ per cycle?

Notice that the slide title is "Energy Cost by Operation Type" - which implies they mean total cost of the whole operation. However, a few lines below they multiply 12000pJ by 3GHz - which implies they mean it is 12000pJ per clock.

... now I am lost. Until this inconsistency is resolved, I take those numbers with a grain of salt.
< Previous Post in ThreadNext Post in Thread >
TopicPosted ByDate
TOP3 blundersanon2009/09/25 07:38 PM
  TOP3 blundersrwessel2009/09/25 07:58 PM
  TOP3 blundersPotatoswatter2009/09/26 02:12 AM
    TOP3 blundersJouni Osmala2009/09/26 08:47 AM
    TOP3 blundersWilco2009/09/26 10:51 AM
      TOP3 blundersPotatoswatter2009/09/26 01:04 PM
        TOP3 blundersRagingDragon2009/09/28 02:58 PM
  TOP3 blunders?2009/09/26 03:44 AM
    TOP3 blundersanon2009/09/26 06:55 AM
      TOP3 blunders?2009/09/26 10:49 AM
        TOP3 blundersPotatoswatter2009/09/26 01:38 PM
        TOP3 blundersJouni Osmala2009/09/26 09:52 PM
          TOP3 blunders?2009/09/27 01:08 AM
            implementationAM2009/09/27 01:31 AM
          the generic mechanismAM2009/09/27 01:15 AM
            the generic mechanism?2009/09/27 02:30 AM
          TOP3 blunderssomeone2009/09/27 07:49 AM
            TOP3 blunders?2009/09/27 08:33 AM
              TOP3 blundersBlistering blue barnacles2009/09/28 08:44 PM
              TOP3 blundersslacker2009/09/29 07:28 AM
                (12nJ/cycle)*3GHz = 36W (NT)Michael S2009/09/29 08:31 AM
                  That's what I get for posting so early. (NT)slacker2009/09/29 06:17 PM
          TOP3 blunderskoby m.2009/09/29 07:26 AM
            TOP3 blundersJouni Osmala2009/09/29 11:05 PM
              TOP3 blunders?2009/09/30 02:26 AM
    TOP3 blundersPotatoswatter2009/09/26 07:11 AM
      TOP3 blunderssomeone2009/09/26 09:26 AM
    ISA extensions - tensilica?David Kanter2009/09/26 10:17 AM
      ISA extensions - StretchWes Felter2009/09/26 11:24 AM
        ISA extensions - Stretch?2009/09/26 01:14 PM
          ISA extensions - StretchGabriele Svelto2009/09/28 03:14 AM
  TOP3 blundersanonymous2009/09/26 06:23 AM
  TOP3 smart movesanonib2009/09/26 07:11 PM
    TOP3 smart movesDavid W. Hess2009/09/26 07:55 PM
      TOP3 smart movesRichard Cownie2009/09/27 01:57 PM
        TOP3 smart movesRagingDragon2009/09/28 03:46 PM
    TOP3 smart movesa reader2009/09/27 08:44 AM
    TOP3 smart movesRichard Cownie2009/09/27 12:12 PM
      TOP2 probably illegal smart movesRichard Cownie2009/09/27 01:43 PM
        TOP2 probably illegal smart movesnn2009/09/27 07:27 PM
        TOP2 probably illegal smart movesDavid Kanter2009/09/29 01:48 AM
          TOP2 probably illegal smart movesRichard Cownie2009/09/29 10:31 AM
            TOP2 probably illegal smart movesMichael S2009/09/29 11:04 AM
              TOP2 probably illegal smart movesDavid Kanter2009/09/29 01:35 PM
              TOP2 probably illegal smart movesRichard Cownie2009/09/29 04:28 PM
              TOP2 probably illegal smart movesJouni Osmala2009/09/29 11:08 PM
              Link to good analysis on the matter.Jouni Osmala2009/09/29 11:22 PM
                Link to good analysis on the matter.Richard Cownie2009/09/30 09:59 AM
  TOP3 blunder of todayMichael S2009/09/29 04:31 AM
Reply to this Topic
Body: No Text
How do you spell purple?