Avoiding ping pong

By: Konrad Schwarz (no.spam.delete@this.no.spam), December 4, 2014 12:10 pm
Room: Moderated Discussions
Aaron Spink (aaronspink.delete@this.notearthlink.net) on December 4, 2014 12:01 pm wrote:
coherency
> protocol is. Assuming some sort of directory/home node protocol, you can do hot line detection (either
> heuristically or explicitly) and export that request to the home node. So for instance, for a CMPXCHG
> type op, you would directly export the CMPXCHG to the home node which would have the line in its hot
> cache. The home node would do the CMPXCHG op, and send back either an ACK or NACK. FETCH_ADD would
> work similarly where you ship the operation to the home node and it does it.

Note that you will also need to return the current or the previous value when the transaction
is successful.

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.

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.

The code base / programmer mindset that relies on atomic operations stems from
a time/from operating systems where such light weight were not available.

> This actually brings me to an architecture area that is of interest to me: Pretty much all architectures
> are still completely cache unaware. Most of out coherency primitives and their functions are designed with
> willful ignorance of the concept of caches. Basically all load store ops are still designed around a model
> where everything is directly connected to a shared bus without caches. Given the modern reality and the
> likelihood of it going forward, there is a lot of optimization space available around making the whole load/store
> ISA space much more cache aware going directly back into the actual

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