I use ALUs

Article: Impressions of Kepler
By: Mark Roulo (nothanks.delete@this.xxx.com), March 23, 2012 3:12 pm
Room: Moderated Discussions
anon (no@thanks.com) on 3/23/12 wrote:
---------------------------
>Mark Roulo (nothanks@xxx.com) on 3/23/12 wrote:
>---------------------------
>>A Kepler has 1.5K for single precision floating point loads.
>>
>>An 8-core SandyBridge has 8x8= 64 for single precision floating point loads.
>>
>>We *still* have to adjust for things like
>>*) clock speed (2.5x - 3x advantage for SandyBridge
>>*) Instructions/clock (edge to SandyBridge)
>
>I think I agree with all your factors except this one. Each of the 8 SMXs has 4
>schedulers, each capable of issuing up to 2 instructions from a single warp per
>clock. I may very well be making a mistake but doesn't that mean 64 instructions
>per clock peak on Kepler vs. 32 on SandyBridge (4 wide issue)? For task level parallelism,
>SandyBridge supports 16 independent programs running in parallel. I have no idea
>what the corresponding number is on Kepler.

This is how I *think* it works.

Kepler has three vector units per schedulers. Each scheduler can dispatch two instructions per clock from a single thread of control (much like 1993 Pentium). In an ideal world, then, the three vector units will stay busy running three ops/clock. Worst case (ignoring memory stalls and such) is two. But you'll never get four.

The key here is that the schedulers are dual-dispatch, but the ALUs are not.

A SandyBridge core *can* issue two ops/clock to three vector unit "ports". This picture shows this:

http://www.hardwaresecrets.com/fullimage.php?image=30986

Because SandyBridge has both hyperthreading and Out-of-order execution, I expect that for numeric code, two instructions get dispatched often.

The dual dispatch for Kepler is "on top" of the ALUs, so not only should we not double count it, but we should probably de-rate it a bit (probably not too much).

I think :-)
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TopicPosted ByDate
First impressions of Nvidia's KeplerDavid Kanter2012/03/22 06:00 PM
  First impressions of Nvidia's Keplerfellix2012/03/23 01:25 AM
  First impressions of Nvidia's KeplerMike2012/03/23 08:24 AM
    First impressions of Nvidia's KeplerDavid Kanter2012/03/23 09:02 AM
      First impressions of Nvidia's KeplerMike2012/03/23 09:34 AM
        First impressions of Nvidia's KeplerDavid Kanter2012/03/23 12:15 PM
      First impressions of Nvidia's Kepleranon2012/03/23 11:37 AM
        I use ALUsMark Roulo2012/03/23 12:59 PM
          I use ALUsanon2012/03/23 02:07 PM
            I use ALUsMark Roulo2012/03/23 03:12 PM
              I use ALUsanon2012/03/23 04:08 PM
        Makes no sense...EduardoS2012/03/23 05:30 PM
          Makes no sense...anon2012/03/23 06:14 PM
            Makes no sense...David Kanter2012/03/25 10:45 AM
          Makes no sense...fellix2012/03/24 05:41 AM
  Comparing against the 560Cat2012/03/26 08:51 AM
    Comparing against the 560David Kanter2012/03/26 09:24 AM
  Shuffle InstructionMartin2012/03/27 06:17 AM
    Shuffle InstructionDavid Kanter2012/03/27 08:47 AM
      Shuffle InstructionMartin2012/03/27 10:52 AM
        .msi unarchiver?hobold2012/03/28 10:20 AM
          .msi unarchiver?Joe2012/03/28 12:55 PM
          .msi unarchiver?Martin2012/03/29 12:53 AM
      Shuffle InstructionRohit2012/03/27 12:04 PM
  Workgroups vs. warps/wavefrontsAndrew McDonald2012/03/28 02:31 PM
    Workgroups vs. warps/wavefrontsDavid Kanter2012/03/28 03:14 PM
      Workgroups vs. warps/wavefrontsRohit2012/03/28 08:53 PM
        Workgroups vs. warps/wavefrontsLee Howes2012/03/29 06:38 AM
          ThreadsDavid Kanter2012/04/09 11:36 AM
    Fixed (NT)David Kanter2012/04/09 11:37 AM
  Heterogeneous GPUsOscar Eddington2012/03/28 07:41 PM
    Heterogeneous GPUsGary M.2012/04/06 04:35 PM
      Different shader coresDavid Kanter2012/04/09 11:29 AM
        Different shader coresTom2012/04/11 02:36 PM
          Nope...David Kanter2012/04/12 01:10 AM
            Nope...Tom2012/04/13 03:58 PM
              Nope...David Kanter2012/04/14 12:24 PM
                Load balancing between Tesla and graphics boardsTom2012/04/15 06:11 PM
                  Load balancing between Tesla and graphics boardsDavid Kanter2012/04/15 10:11 PM
                    Load balancing between Tesla and graphics boardsAnon2012/04/16 05:05 PM
  Why isn't AMD hardware used for GPU computing?Richard G.2012/04/03 07:39 PM
    Why isn't AMD hardware used for GPU computing?anon2012/04/04 03:11 AM
      Why isn't AMD hardware used for GPU computing?Soupdragon2012/04/04 05:24 AM
        Why isn't AMD hardware used for GPU computing?Groo2012/04/04 08:41 AM
      Why isn't AMD hardware used for GPU computing?Michael S2012/04/04 06:24 AM
      Why isn't AMD hardware used for GPU computing?Alexko2012/04/04 08:43 AM
        Why isn't AMD hardware used for GPU computing?EduardoS2012/04/04 03:37 PM
          Why isn't AMD hardware used for GPU computing?David Kanter2012/04/09 02:51 PM
    Why isn't AMD hardware used for GPU computing?Ricardo B2012/04/04 12:57 PM
    Why isn't AMD hardware used for GPU computing?Tom2012/04/04 05:36 PM
      Why isn't AMD hardware used for GPU computing?Brett2012/04/04 06:55 PM
      Why isn't AMD hardware used for GPU computing?David Kanter2012/04/09 02:55 PM
  Predictions about KeplerRussell Baker2012/04/18 02:09 PM
    Predictions about Kepler01000102012/04/18 03:14 PM
      Predictions about KeplerEduardoS2012/04/18 03:38 PM
        Predictions about KeplerAnon2012/04/18 08:48 PM
          Predictions about KeplerEduardoS2012/04/19 03:03 PM
            Predictions about KeplerMeeps2012/04/19 03:39 PM
      Predictions about KeplerJohn P.2012/04/18 06:13 PM
      Predictions about KeplerFoo_2012/04/19 12:15 PM
        Predictions about KeplerEduardoS2012/04/19 03:07 PM
    Predictions about KeplerGroo2012/04/19 09:13 AM
      Predictions about Kepleranon2012/04/19 03:26 PM
        Predictions about KeplerGroo2012/04/20 08:01 AM
    Predictions about KeplerAlex L.2012/04/20 03:41 PM
      Predictions about KeplerAnon2012/04/21 09:34 AM
        Predictions about Keplermpx2012/04/21 11:23 PM
          Predictions about Keplerac2012/04/22 01:49 AM
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