Transactional memory

Article: Knights Landing CPU Speculation
By: Bhima (Bhima.Pandava.delete@this.gmail.com), November 25, 2013 8:01 am
Room: Moderated Discussions
Patrick Chase (patrickjchase.delete@this.hp.com) on November 23, 2013 3:37 pm wrote:
> David's article claims: "Similarly, features like transactional memory are not likely
> to be useful for Knights Landing and represent an added implementation cost."
>
> I think this may be incorrect, based on 2 observations:
>
> 1. IBM's BG/Q is targeted at roughly the same market, and was the first POWER-family processor
> to implement TM. Furthermore, I have acquaintances who work with Sequoia (LLNL's million-node
> BG/Q) and who claim that the TM capability is in fact useful for their workloads.
>
> 2. Intel's TM benchmarks in the infamous paper were heavily HPC-skewed, and showed significant benefit in programmer
> productivity for HPC loads. Specifically, the paper demonstrated that TM enabled several loads to use coarse-grained
> locking while achieving comparable performance to non-TM versions with fine-grained locking.
>
> I would also argue that a lot of people in this forum missed the point when they criticized Intel's
> TM results because they didn't show outright performance gains relative to fine-grained locking.
> TM is more about productivity/convenience than about absolute performance. If you're willing to go
> to the trouble of implementing and debugging arbitrarily fine-grained locking then you should (barring
> certain pathological cases) achieve similar or better performance as compared to TM.
>
> The real benefit is that with TM you can often get close to that performance with
> a "naive", coarse-grained locking implementation that takes an order of magnitude
> less effort to develop. Real world HPC folks care deeply about that sort of thing...

I'm really glad you brought this up because when I read this I was a bit confused with that statement as it was my understanding that the motivations to include transactional memory in the other Xeons were in part to simplify memory management for the many parallel processes that having all those cores & threads (in the regular Xeons) enables. As Knights Landing has more cores and more hyperthreading, I was thinking that, for some sorts of processing at least, transactional memory would be equally or even more beneficial.

Hopefully, this topic will be included in the upcoming article and more fully discussed. I find the concept of transactional memory intriguing but clearly I must be misunderstanding something important.
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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 Speculation2013/11/26 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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