Article: Knights Landing CPU Speculation
By: Sylvain Collange (firstname.lastname.delete@this.gmail.com), November 24, 2013 3:37 am
Room: Moderated Discussions
Michael S (already5chosen.delete@this.yahoo.com) on November 21, 2013 6:48 am wrote:
> 2 FPUs on 2-issue core? That's silly. 2-issue is barely enough to keep one FPU reasonably busy.

That is certainly true for most scalar workloads, but vector-intensive code can easily saturate a single vector unit. An FMA pipeline typically runs SIMD integer instructions in addition to FP instructions.

In SPMD-style code such as OpenCL, every variable is a vector unless the compiler can prove it holds the same value for all threads of a warp. Even assuming an omniscient compiler, scalar instructions only represent about 30% of the instruction mix, and less with agressive unrolling. Thus vector performance matters.
Fermi and Kepler already have 2 FMAs for each scheduler, and can sustain the peak issue rate on a 100% FMA instruction mix.

A 2-issue core with dual-FMA is the most sensible option in my opinion.
I am much more skeptical about out-of-order execution of a fully mask-predicated instruction set...
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TopicPosted ByDate
Knights Landing CPU SpeculationDavid Kanter2013/11/18 03:03 AM
  Knights Landing CPU Speculationnone2013/11/18 03:59 AM
    Knights Landing CPU SpeculationPatrick Chase2013/11/23 04:18 PM
      Knights Landing CPU SpeculationAdam Kalisz2013/11/26 02:20 AM
        Over 2,000 mm^2 of eDRAM???Mark Roulo2013/11/26 10:28 AM
          Over 2,000 mm^2 of eDRAM???David Kanter2013/11/26 12:09 PM
          Over 2,000 mm^2 of eDRAM???Eric Bron2013/11/26 12:21 PM
            Over 2,000 mm^2 of eDRAM???tarlinian2013/11/26 12:50 PM
              Over 2,000 mm^2 of eDRAM???Eric Bron2013/11/26 02:07 PM
                Over 2,000 mm^2 of eDRAM???Eric Bron2013/11/26 02:09 PM
                Over 2,000 mm^2 of eDRAM???aaron spink2013/11/26 04:03 PM
                  Over 2,000 mm^2 of eDRAM???Eric Bron2013/11/27 12:42 AM
                    Over 2,000 mm^2 of eDRAM???aaron spink2013/11/27 11:31 AM
              Over 2,000 mm^2 of eDRAM???David Kanter2013/11/26 05:25 PM
                Over 2,000 mm^2 of eDRAM???tarlinian2013/11/26 08:01 PM
          Over 2,000 mm^2 of eDRAM???Eric2013/11/27 03:54 AM
            eDRAM is DRAM in a logic-oriented processPaul A. Clayton2013/11/27 08:10 AM
  Knights Landing CPU SpeculationJames2013/11/18 06:26 AM
    Knights Landing CPU SpeculationMichael S2013/11/18 03:57 PM
      Knights Landing CPU SpeculationUrban Novak2013/11/19 01:49 AM
        Knights Landing CPU Speculationnone2013/11/19 02:19 AM
          Knights Landing CPU SpeculationEric2013/11/19 08:48 PM
            Total GPGPU/Xeon Phi market maybe ~ $500M/year ...Mark Roulo2013/11/20 11:35 AM
      Knights Landing CPU SpeculationWes Felter2013/11/19 01:06 PM
        Knights Landing CPU SpeculationMichael S2013/11/19 01:49 PM
  Knights Landing CPU SpeculationEric2013/11/18 01:17 PM
    Knights Landing CPU SpeculationDaniel2013/11/19 03:28 AM
      Knights Landing CPU SpeculationEric2013/11/19 08:36 PM
      HPC guys score FLOPS non-obviouslyMark Roulo2013/11/20 11:43 AM
        3-TFlops-DGEMMMichael S2013/11/20 11:59 AM
          3-TFlops-DGEMMMark Roulo2013/11/20 01:22 PM
            3-TFlops-DGEMMDaniel2013/11/20 02:04 PM
              3-TFlops-DGEMMEric2013/11/21 02:28 AM
                3-TFlops-DGEMMMichael S2013/11/21 06:48 AM
                  3-TFlops-DGEMMRecessionCone2013/11/21 12:13 PM
                    3-TFlops-DGEMMMichael S2013/11/21 03:34 PM
                  3-TFlops-DGEMMEric2013/11/22 03:10 AM
                    3-TFlops-DGEMMMichael S2013/11/22 05:41 AM
                    A (not very sensible) alternative: FMADD + FADDPaul A. Clayton2013/11/22 09:19 AM
                  3-TFlops-DGEMMSylvain Collange2013/11/24 03:37 AM
                    3-TFlops-DGEMMMichael S2013/11/24 07:06 AM
                      3-TFlops-DGEMMSylvain Collange2013/11/24 10:28 AM
        HPC guys score FLOPS non-obviouslyPatrick Chase2013/11/23 03:58 PM
  Knights Landing CPU SpeculationPaul Caheny2013/11/18 02:25 PM
    Knights Landing CPU SpeculationKonrad Schwarz2013/11/19 01:24 AM
  Knights Landing CPU SpeculationAmiba Gelos2013/11/19 08:36 PM
    Knights Landing CPU SpeculationDavid Kanter2013/11/20 10:52 AM
    Knights Landing CPU SpeculationLinus Torvalds2013/11/21 03:12 PM
      Knights Landing CPU SpeculationAmiba Gelos2013/11/21 06:14 PM
      Knights Landing CPU SpeculationPatrick Chase2013/11/23 04:33 PM
        Knights Landing CPU SpeculationLinus Torvalds2013/11/25 12:29 PM
          Knights Landing CPU SpeculationLinus Torvalds2013/11/25 01:05 PM
          Knights Landing CPU SpeculationPatrick Chase2013/11/25 01:22 PM
            Knights Landing CPU SpeculationLinus Torvalds2013/11/26 11:11 AM
          Knights Landing CPU SpeculationEric2013/11/26 04:05 AM
            Knights Landing CPU SpeculationEric2013/11/26 04:15 AM
            Knights Landing CPU Speculationnone2013/11/26 04:33 AM
              Knights Landing CPU SpeculationEric2013/11/26 07:30 PM
                Knights Landing CPU SpeculationEric2013/11/26 07:34 PM
                  What is MCDRAM?anon2013/11/26 09:58 PM
                    What is MCDRAM?none2013/11/27 02:00 AM
                      What is MCDRAM?Klimax2013/11/27 03:19 AM
                  Knights Landing CPU SpeculationKlimax2013/11/27 12:06 AM
                Knights Landing CPU SpeculationKlimax2013/11/27 12:05 AM
            Knights Landing CPU Speculationanon2013/11/26 06:53 AM
              Knights Landing CPU Speculationnone2013/11/26 07:20 AM
                Knights Landing CPU SpeculationMichael S2013/11/26 09:06 AM
                  Knights Landing CPU Speculationnone2013/11/26 10:18 AM
                    Knights Landing CPU SpeculationEric Bron2013/11/26 02:21 PM
                      Knights Landing CPU SpeculationEric Bron2013/11/26 02:27 PM
                        Knights Landing CPU Speculationnone2013/11/26 03:26 PM
                    Knights Landing CPU Speculationanon2013/11/26 06:42 PM
                      Knights Landing CPU Speculationnone2013/11/27 02:08 AM
                        Knights Landing CPU Speculationanon2013/11/27 02:50 AM
                          Knights Landing CPU Speculationnone2013/11/27 02:58 AM
                      Knights Landing CPU SpeculationMichael S2013/11/27 02:25 AM
                        Knights Landing CPU Speculationanon2013/11/27 03:32 AM
                          Knights Landing CPU SpeculationMichael S2013/11/27 04:08 AM
    Knights Landing CPU SpeculationChung Leong2013/11/27 02:28 AM
      Knights Landing CPU SpeculationMichael S2013/11/27 03:53 AM
        Knights Landing CPU SpeculationChung Leong2013/11/27 02:03 PM
  BiG.LiTTLe for KNL?Jeff K2013/11/22 07:17 AM
    BiG.LiTTLe for KNL?Patrick Chase2013/11/23 03:54 PM
      BiG.LiTTLe for KNL?Patrick Chase2013/11/23 04:01 PM
  Transactional memoryPatrick Chase2013/11/23 03:37 PM
    Transactional memoryBhima2013/11/25 08:01 AM
      Transactional memoryPatrick Chase2013/11/25 12:52 PM
  Knights Landing CPU SpeculationDaniel2013/11/25 03:17 AM
    Knights Landing CPU SpeculationKlimax2013/11/25 04:12 AM
    Knights Landing CPU Speculationnone2013/11/25 05:05 AM
      Knights Landing CPU SpeculationKlimax2013/11/25 05:45 AM
        Knights Landing CPU Speculationnone2013/11/25 05:55 AM
          Knights Landing CPU Speculationgmb2013/11/25 08:21 AM
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