ISA != interface for "most programmers"

By: rwessel (robertwessel.delete@this.yahoo.com), December 4, 2014 7:50 pm
Room: Moderated Discussions
Paul A. Clayton (paaronclayton.delete@this.gmail.com) on December 4, 2014 3:34 pm wrote:
> Konrad Schwarz (no.spam.delete@this.no.spam) on December 4, 2014 1:10 pm wrote:
> [snip]
>
> > Note that you will also need to return the current or the previous value when the transaction
> > is successful.
>
> Yes, at least if the operation was not "fire-and-forget". Yet that could still be lower
> latency and lower bandwidth than using ordinary coherence for such hot line updates.
>
> > I'm no expert in VLSI design, but this seems like a large increase in complexity in the coherency
> > protocol for a modest benefit. I find it more likely that the line in question is protected from
> > eviction from the local cache for a short period of time. My understanding is that this is
> > basically how modern x86 implements atomic operations on cacheable memory.
>
> The "modest benefit" might be a bottleneck for scalable systems. I.e., if another
> bottleneck is what limits such to a modest benefit, when that other bottleneck is
> removed such high contention updates might become the next significant bottleneck.
>
> > And honestly, I still think most programmers would be better served by using ligh weight (in the
> > uncontended case) synchronization objects provided by the OS (i.e., mutex/condition variables)
> > rather than employing atomic operations directly.
>
> From a relatively uninformed perspective (compared to others here), I think most programmers would
> be better served by not having an extremely detailed view of the ISA and microarchitecture. I suspect
> most of these matters can be abstracted by the compiler, libraries, runtime system, OS, etc. without
> a substantial abstraction penalty. Perhaps I am overestimating the quality of compilers (or the optimization
> levels typically used) et al.


See Proebsting’s Law (and *I* think he was being optimistic!). Despite all the hoopla, compilers mostly suck at optimization. About the only thing that does a worse job of optimization is the average programmer.

Sure, we've all seen impressive cases of optimization - heck I've been impressed by many of the AVX vectorizations that ICC can do. But again and again those turn out to be terribly fragile, and just don't make much difference on the vast majority of code.


>It seems to me that generally a programmer should seek to communicate
> intent more than specific implementation. Data structure and algorithm choices do communicate certain
> expectations because of their tradeoffs, even dipping into assembly often communicates an expectation
> that a small section is performance critical, but it seems that
>
> I do think that allowing programmers to provide an implementation that is semantically equivalent to a higher-level
> expression would be useful. In some cases, such low-level implementations might not be provably equivalent or
> might seem (to the compiler) inferior, so an annotation might be needed to tell the compiler to use this implementation.
> However, I suspect that most programming languages have much higher priority issues.


Higher level expression of programs is a good idea. Good enough that a ten fold reduction in performance is absolutely worth it in 99% of cases. And much of the computing world is built on far worse performance than that. Just consider the vast use of scripting languages in web servers.
< Previous Post in ThreadNext Post in Thread >
TopicPosted ByDate
ARMv8 getting atomic operationsdmcq2014/12/02 05:32 PM
  ARMv8 getting atomic operationsMaynard Handley2014/12/02 07:33 PM
    ARMv8 getting atomic operationsDoug S2014/12/02 10:30 PM
      ARMv8 getting atomic operationsdmcq2014/12/03 03:16 AM
      ARMv8 getting atomic operationsMaynard Handley2014/12/03 09:20 AM
      ARMv8 getting atomic operationsBrett2014/12/03 04:46 PM
    ARMv8 getting atomic operationsAndreas2014/12/03 06:51 AM
      ARMv8 getting atomic operationsLinus Torvalds2014/12/03 11:15 AM
        ARMv8 getting atomic operationsanon2014/12/03 05:08 PM
          Guaranteed transactionsPaul A. Clayton2014/12/03 08:04 PM
            Guaranteed transactionsanon2014/12/03 08:38 PM
              Avoiding ping pongPaul A. Clayton2014/12/04 09:11 AM
                Avoiding ping ponganon2014/12/04 10:15 AM
                  OoO window is limitedPaul A. Clayton2014/12/04 01:06 PM
                Avoiding ping pongAaron Spink2014/12/04 12:01 PM
                  Avoiding ping pongKonrad Schwarz2014/12/04 01:10 PM
                    Avoiding ping pongAaron Spink2014/12/04 02:31 PM
                    Avoiding ping pongGabriele Svelto2014/12/04 02:49 PM
                      Avoiding ping pongKonrad Schwarz2014/12/04 11:08 PM
                        Avoiding ping pongGabriele Svelto2014/12/05 12:04 AM
                          Avoiding ping pongEric Bron nli2014/12/05 02:28 AM
                            Avoiding ping pongKonrad Schwarz2014/12/05 03:37 AM
                              Avoiding ping pongEric Bron nli2014/12/05 04:23 AM
                                Avoiding ping pongKlimax2014/12/05 05:47 AM
                                  Avoiding ping pongEric Bron2014/12/05 06:24 AM
                              Avoiding ping pongGabriele Svelto2014/12/05 10:38 AM
                                Avoiding ping pongKonrad Schwarz2014/12/07 02:28 PM
                                  Avoiding ping pongGabriele Svelto2014/12/08 07:10 PM
                                    Avoiding ping pongKonrad Schwarz2014/12/09 05:12 AM
                                      Avoiding ping pongGabriele Svelto2014/12/09 07:31 AM
                                        Avoiding ping ponganon2014/12/09 11:24 PM
                            Avoiding ping pongGabriele Svelto2014/12/05 10:17 AM
                              Avoiding ping pongEric Bron2014/12/05 10:32 AM
                                Avoiding ping pongGabriele Svelto2014/12/05 12:45 PM
                                  Avoiding ping pongEric Bron2014/12/06 02:20 AM
                                    Avoiding ping pongnksingh2014/12/06 03:42 AM
                                      Avoiding ping pongEric Bron2014/12/06 04:04 AM
                                        Avoiding ping pongGiGNiC2014/12/06 06:27 AM
                                          Avoiding ping pongEric Bron nli2014/12/06 06:44 AM
                                          Avoiding ping pongEric Bron2014/12/06 07:07 AM
                                            Avoiding ping pongnksingh2014/12/07 04:06 PM
                                              Avoiding ping pongEric Bron2014/12/08 04:17 AM
                                                Avoiding ping pongGiGNiC2014/12/08 11:53 AM
                                                Avoiding ping pongnksingh2014/12/08 05:53 PM
                                                  Avoiding ping pongEric Bron2014/12/09 01:33 AM
                                    Avoiding ping pongdmsc2014/12/06 04:12 AM
                                      Avoiding ping pongEric Bron2014/12/06 04:25 AM
                                        Avoiding ping pongKlimax2014/12/06 05:49 AM
                                          Avoiding ping pongrwessel2014/12/07 02:34 AM
                                        Avoiding ping pongdmsc2014/12/06 07:39 AM
                                        Avoiding ping pongKonrad Schwarz2014/12/07 02:37 PM
                                          Avoiding ping pongMichael S2014/12/07 04:37 PM
                                            Avoiding ping pongKonrad Schwarz2014/12/08 04:35 AM
                          Avoiding ping pongKonrad Schwarz2014/12/05 03:30 AM
                        Avoiding ping pongLinus Torvalds2014/12/05 12:58 PM
                          Avoiding ping pongEric Bron2014/12/06 02:42 AM
                            Avoiding ping pongnksingh2014/12/06 03:51 AM
                              Avoiding ping pongEric Bron2014/12/06 04:08 AM
                            Avoiding ping pongLinus Torvalds2014/12/06 01:25 PM
                              Avoiding ping pongnksingh2014/12/07 03:26 PM
                                Avoiding ping pongEric Bron2014/12/08 04:35 AM
                                  Avoiding ping pongBrett2014/12/08 10:00 AM
                                    Avoiding ping pongEric Bron2014/12/08 10:48 AM
                                    Avoiding ping pongrwessel2014/12/08 12:52 PM
                                      Avoiding ping pongBrett2014/12/08 01:58 PM
                                      Avoiding ping pongDoug S2014/12/08 02:04 PM
                              Avoiding ping pongJouni Osmala2014/12/08 02:45 AM
                                Avoiding ping ponganon2014/12/08 05:44 AM
                                  Avoiding ping pongJouni Osmala2014/12/08 01:10 PM
                                    Avoiding ping pongLinus Torvalds2014/12/08 01:34 PM
                                      Avoiding ping pongJouni Osmala2014/12/08 03:47 PM
                                        Avoiding ping pongLinus Torvalds2014/12/08 08:08 PM
                                          Avoiding ping pongGabriele Svelto2014/12/09 07:48 AM
                                            Avoiding ping pongMaynard Handley2014/12/09 11:41 AM
                                              Avoiding ping pongPatrick Chase2014/12/09 01:06 PM
                                              Avoiding ping pongGabriele Svelto2014/12/09 01:52 PM
                                                Avoiding ping pongPatrick Chase2014/12/09 02:08 PM
                                            Why read RWT or Reddit when you can get journalists to do it for you?Rob Thorpe2015/01/02 08:20 AM
                                              Why read RWT or Reddit when you can get journalists to do it for you?juanrga2015/01/02 11:21 AM
                                                Why read RWT or Reddit when you can get journalists to do it for you?EduardoS2015/01/02 11:37 AM
                                                  Why read RWT or Reddit when you can get journalists to do it for you?juanrga2015/01/03 12:00 PM
                                                Why read RWT or Reddit when you can get journalists to do it for you?Eric Bron nli2015/01/02 02:28 PM
                                                  Why read RWT or Reddit when you can get journalists to do it for you?juanrga2015/01/03 12:02 PM
                                                    Why read RWT or Reddit when you can get journalists to do it for you?Michael S2015/01/03 12:36 PM
                                                      Why read RWT or Reddit when you can get journalists to do it for you?juanrga2015/01/03 01:11 PM
                                                        Why read RWT or Reddit when you can get journalists to do it for you?Michael S2015/01/03 01:30 PM
                                                          Why read RWT or Reddit when you can get journalists to do it for you?Eric Bron2015/01/03 02:57 PM
                                                            KNL cacheDavid Kanter2015/01/03 07:36 PM
                                                              KNL cacheEric Bron2015/01/04 03:34 AM
                                                                KNL cacheMichael S2015/01/04 04:11 AM
                                                                  KNL cacheEric Bron2015/01/04 04:57 AM
                                                                    KNL cacheMichael S2015/01/04 05:21 AM
                                                                      KNL cacheEric Bron2015/01/04 05:58 AM
                                                          Why read RWT or Reddit when you can get journalists to do it for you?juanrga2015/01/07 05:47 AM
                                                            Why read RWT or Reddit when you can get journalists to do it for you?Michael S2015/01/07 08:27 AM
                                                              Manycores vs multicoresjuanrga2015/01/10 04:10 PM
                                                                Manycores vs multicoresAaron Spink2015/01/10 05:32 PM
                                                                  Manycores vs multicoresjuanrga2015/01/10 06:32 PM
                                                                    Manycores vs multicoresExophase2015/01/10 06:49 PM
                                                                      Manycores vs multicoresjuanrga2015/01/10 08:21 PM
                                                                        Manycores vs multicoresExophase2015/01/10 08:51 PM
                                                                        Manycores vs multicoresAaron Spink2015/01/10 09:03 PM
                                                                    Manycores vs multicoresAaron Spink2015/01/10 07:21 PM
                                                                      Manycores vs multicoresjuanrga2015/01/10 08:25 PM
                                                                        Manycores vs multicoresAaron Spink2015/01/10 09:11 PM
                                                                          Manycores vs multicoresJouni Osmala2015/01/11 04:50 AM
                                                                            Manycores vs multicoresjuanrga2015/01/11 08:58 AM
                                                                            Manycores vs multicorescoppice2015/01/12 10:01 PM
                                                                              Manycores vs multicoresJouni Osmala2015/01/13 04:38 AM
                                                                        Manycores vs multicoresanon2015/01/11 03:19 AM
                                                                      Manycores vs multicoresMichael S2015/01/11 05:44 AM
                                                                        Manycores vs multicoresAaron Spink2015/01/11 05:55 PM
                                                                          Manycores vs multicoresMichael S2015/01/12 04:41 AM
                                                                            Manycores vs multicoresEric Bron2015/01/12 06:29 AM
                                                                              Manycores vs multicoresEric Bron2015/01/12 06:30 AM
                                                        Why read RWT or Reddit when you can get journalists to do it for you?Eric Bron2015/01/03 02:54 PM
                                                          Why read RWT or Reddit when you can get journalists to do it for you?juanrga2015/01/07 05:48 AM
                                                            Why read RWT or Reddit when you can get journalists to do it for you?Eric Bron2015/01/07 07:41 AM
                                                              Manycores vs multicoresjuanrga2015/01/10 04:14 PM
                                                    Why read RWT or Reddit when you can get journalists to do it for you?Eric Bron2015/01/03 02:42 PM
                                                      Why read RWT or Reddit when you can get journalists to do it for you?juanrga2015/01/07 06:03 AM
                                                        Why read RWT or Reddit when you can get journalists to do it for you?Eric Bron2015/01/07 07:45 AM
                                                        Why read RWT or Reddit when you can get journalists to do it for you?Linus Torvalds2015/01/08 03:09 PM
                                                          Pink unicorns for salejuanrga2015/01/10 05:09 PM
                                                        Intentionally picking a competitors slow part is cheating ...Mark Roulo2015/01/08 06:37 PM
                                                          Intentionally picking a competitors slow part is cheating ...coppice2015/01/08 11:38 PM
                                                            Intentionally picking a competitors slow part is cheating ...Mark Roulo2015/01/09 09:13 AM
                                                              Intentionally picking a competitors slow part is cheating ...Anon2015/01/10 02:00 AM
                                                              Intentionally picking a competitors slow part is cheating ...David Hess2015/01/11 01:03 PM
                                                            Intentionally picking a competitors slow part is cheating ...someone2015/01/09 10:31 AM
                                                              Intentionally picking a competitors slow part is cheating ...coppice2015/01/12 09:45 PM
                                                                Intentionally picking a competitors slow part is cheating ...coppice2015/01/12 09:47 PM
                                                                  Intentionally picking a competitors slow part is cheating ...Michael S2015/01/13 07:53 AM
                                                                    Intentionally picking a competitors slow part is cheating ...coppice2015/01/13 09:44 AM
                                                                      Intentionally picking a competitors slow part is cheating ...Michael S2015/01/13 10:01 AM
                                                                        Intentionally picking a competitors slow part is cheating ...coppice2015/01/13 08:35 PM
                                                                      Core sizesjuanrga2015/01/13 12:28 PM
                                                          NVIDIA'S FIRST CPU IS A WINNER (Linley Gwennap)juanrga2015/01/10 04:34 PM
                                                        Why read RWT or Reddit when you can get journalists to do it for you?Patrick Chase2015/01/08 07:02 PM
                                                        Why read RWT or Reddit when you can get journalists to do it for you?coppice2015/01/08 10:18 PM
                                                          Why read RWT or Reddit when you can get journalists to do it for you?Patrick Chase2015/01/09 11:54 AM
                                                            Why read RWT or Reddit when you can get journalists to do it for you?Mark Roulo2015/01/09 12:59 PM
                                                              Why read RWT or Reddit when you can get journalists to do it for you?Patrick Chase2015/01/09 03:20 PM
                                                                Why read RWT or Reddit when you can get journalists to do it for you?Eric Bron2015/01/09 03:30 PM
                                                            Alternatives to OOOE (again)juanrga2015/01/10 04:50 PM
                                                              Alternatives to OOOE (again)David Kanter2015/01/11 12:10 AM
                                                                Alternatives to OOOE (again)juanrga2015/01/11 08:30 AM
                                                            Why read RWT or Reddit when you can get journalists to do it for you?Gabriele Svelto2015/01/11 12:53 AM
                                              Why read RWT or Reddit when you can get journalists to do it for you?Fake Linus Torvalds2015/01/03 12:14 PM
                                                Why read RWT or Reddit when you can get journalists to do it for you?Rob Thorpe2015/01/03 08:25 PM
                                          Avoiding ping pongMaynard Handley2014/12/09 11:33 AM
                                            Avoiding ping pongPatrick Chase2014/12/09 01:54 PM
                                              Avoiding ping pongMaynard Handley2014/12/09 06:56 PM
                                      Avoiding ping pongSalvatore De Dominicis2014/12/09 08:51 AM
                                        Avoiding ping pongPatrick Chase2014/12/09 02:00 PM
                                      Avoiding ping pongook2014/12/11 03:31 AM
                                      Avoiding ping pongArt Scott2014/12/19 10:19 PM
                                        Avoiding ping pongEric Bron nli2014/12/20 04:05 AM
                                      What about specialization?Troll?2015/01/02 07:55 AM
                                        What about specialization?Ungo2015/01/04 03:27 PM
                                      Avoiding ping pongfewwef2015/01/05 08:16 PM
                                      Avoiding ping pongV.Krishn2015/01/08 06:11 AM
                                    Avoiding ping pongGabriele Svelto2014/12/08 07:32 PM
                                    Avoiding ping ponganon2014/12/08 11:37 PM
                            Avoiding ping pongKonrad Schwarz2014/12/10 06:23 AM
                              Avoiding ping pongLinus Torvalds2014/12/10 11:56 AM
                          Object reference lockingDavid W2014/12/08 11:36 PM
                            Object reference lockingPatrick Chase2014/12/09 04:52 PM
                              Object reference lockingDavid W2014/12/11 05:18 AM
                    ISA != interface for "most programmers"Paul A. Clayton2014/12/04 03:34 PM
                      ISA != interface for "most programmers"rwessel2014/12/04 07:50 PM
                  Interesting! (exporting hot lines/cache-aware ISA); "Please sir, I want some more" (NT)Paul A. Clayton2014/12/04 02:26 PM
                  Avoiding ping pongMichael S2014/12/06 03:48 PM
          ARMv8 getting atomic operationsLinus Torvalds2014/12/04 12:05 PM
            LL/SC idiom recognition is not admitting RMW superiorityPaul A. Clayton2014/12/04 02:34 PM
            ARMv8 getting atomic operationsanon2014/12/04 10:17 PM
    ARMv8 getting atomic operationsPatrick Chase2014/12/03 12:09 PM
  limited ordernksingh2014/12/04 10:17 PM
    I didn't understand this either. (NT)Konrad Schwarz2014/12/04 10:32 PM
    limited orderdmcq2014/12/05 02:13 AM
    limited orderbakaneko2014/12/05 09:11 AM
Reply to this Topic
Name:
Email:
Topic:
Body: No Text
How do you spell tangerine? 🍊