Quick Question on PS3 CPU

Discussion in 'Console Technology' started by Ardrid, May 17, 2005.

  1. Ardrid

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    I didn't want to derail the E3 threads, so I figured I just post this question as a separate topic. Does anyone know the formula for GFLOPS? I've been banging my head against the wall trying to figure out where in the hell they're getting 218 GFLOPS from. Thanks in advance guys.
     
  2. ERP

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    Just guessing

    (7+1)*8*3.2 + 4*3.2 = 217.6 = 218 in marketing speak

    the 4 is from the float core on the PPC, the rest is from the SIMD units on each of the processors.
     
  3. Ardrid

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    Ok, that makes sense. The only thing that's confusing me now are Cell's original numbers at 4GHz. They said that one Cell was capable of 256 GFLOPS due to each of the 8 SPEs being capable of 32 GFLOPS. Where did the PPC go in that case?
     
  4. ERP

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    They probably weren't as desperate to count it to make the numbers look better.
     
  5. Shifty Geezer

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    In that case it was >256 GFlops. The 256 GFlops was just for the SPUs. PPU added some 10% or so, not even that.
     
  6. Panajev2001a

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    Total FP ops count = (7 SPE's * 8 FP ops/SPE) + (1 PPE * 12 FP ops/PPE) = 68 FP ops/cycle.

    So, 3.2 GHz * 68 = 217.6 GFLOPS = 218 GFLOPS.

    I think they share the same FPU as the cores in Xenon's CPU: an FPU that can co-issue with VMX and that has a 2-way SIMD mode for 4FP ops/cycle... the FPU can either do scalar 64 bits DP FP operations or 2-way SIMD operations on single precision FP operations like Gekko's FPU in GameCube).
     
  7. Squeak

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    One more question:
    What's with the "keeping one SPE for redundancy" thing?
    Is that really necessary, I mean one whole SPE?! That's a lot of processing power to keep redundant.
     
  8. Panajev2001a

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    It is for yields: the same principle used for SRAM blocks and e-DRAM blocks. IF you ahve some more identical blocks extra, if one block in the produced chip does nto work, you have another one that can be used in its place and the chip although havign a defect cans till work at full specs and be sold as such :).
     
  9. Tim

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    It is not like you can have less than one for redundancy and 12.5% for redundancy is not especially much.
     
  10. j^aws

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    I know!!

    It's ~25.6 GFlops per SPE...that's like 4 Emotion Engines! :shock:

    Personally, I think they come alive once you activate an in-game cheat so that you can kick some ass! :p
     
  11. London Geezer

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    My question is, is the 8th SPE in there, but just not active? Why would they do that? I'm sure by the time PS3 launches, things will be easier on the Cell front and they should be able to have the full thing working at decent clockspeeds...

    And what's with the 7-trend all of a sudden? 7 SPEs, 7 controllers... :?
     
  12. Tim

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    It is there, it might be broken. Having redundancy increases yields, if there is an error in a the chip the SPE where the error can be disabled and the chip sold as a 1+7 chip instead of being thrown away - this reduces overall cost.

    Redundancy is nothing new there has always been redundant cache lines, the new is that cores in multi core design is used for redundancy.
     
  13. London Geezer

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    But they still have almost and entire year to get this chip right. That's a lot of time in processors terms...
     
  14. Squeak

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    Oh that's a pretty smart idea. That, together with the dinnerplate sized wafers, should help keeping costs down.
    I remember reading about Clive Sinclair experimenting with the same idea, only on giant ROM wafers, as an alternative to floppy discs. :eek:

    Edit: This means that they could even use chips with only a few functioning SPEs for other applications. Maybe Cell is in fact a very cost effective design, more so than we thought at least.
     
  15. sytaylor

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    They'll still loose some chips, no matter how good their fabs are, this means they can ship one with just 7 working as apposed to having to throw it away. What bothers me is that some good performance will come without touching the 7 SPE's, and I think we'll see a lot of games that make little or no use of them in the early stages.
     
  16. Squeak

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    That would be absolutely insane! Poor use? Yes maybe. But no use? Never. Sony wouldn't allow such a game to be released
     
  17. London Geezer

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    Jesus sy!! That's a bit stretching it! That would be like releasing a game for a single core G5 (or less) and two 6800U SLI!! No sense at all. :wink:
     
  18. sytaylor

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    If it sells, I don't see why not? Games like Splinter Cell that are cross console etc (ports) are most likley candidates.
     
  19. London Geezer

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    I think we can rest assured that no game that only uses the PPE core and no SPEs will ever ship.
     
  20. sytaylor

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    *Clinches blanket* :oops:
     
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