Avoiding ping pong

By: Konrad Schwarz (no.spam.delete@this.no.spam), December 4, 2014 1:10 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 operationsdmcq12/02/14 05:32 PM
  ARMv8 getting atomic operationsMaynard Handley12/02/14 07:33 PM
    ARMv8 getting atomic operationsDoug S12/02/14 10:30 PM
      ARMv8 getting atomic operationsdmcq12/03/14 03:16 AM
      ARMv8 getting atomic operationsMaynard Handley12/03/14 09:20 AM
      ARMv8 getting atomic operationsBrett12/03/14 04:46 PM
    ARMv8 getting atomic operationsAndreas12/03/14 06:51 AM
      ARMv8 getting atomic operationsLinus Torvalds12/03/14 11:15 AM
        ARMv8 getting atomic operationsanon12/03/14 05:08 PM
          Guaranteed transactionsPaul A. Clayton12/03/14 08:04 PM
            Guaranteed transactionsanon12/03/14 08:38 PM
              Avoiding ping pongPaul A. Clayton12/04/14 09:11 AM
                Avoiding ping ponganon12/04/14 10:15 AM
                  OoO window is limitedPaul A. Clayton12/04/14 01:06 PM
                Avoiding ping pongAaron Spink12/04/14 12:01 PM
                  Avoiding ping pongKonrad Schwarz12/04/14 01:10 PM
                    Avoiding ping pongAaron Spink12/04/14 02:31 PM
                    Avoiding ping pongGabriele Svelto12/04/14 02:49 PM
                      Avoiding ping pongKonrad Schwarz12/04/14 11:08 PM
                        Avoiding ping pongGabriele Svelto12/05/14 12:04 AM
                          Avoiding ping pongEric Bron nli12/05/14 02:28 AM
                            Avoiding ping pongKonrad Schwarz12/05/14 03:37 AM
                              Avoiding ping pongEric Bron nli12/05/14 04:23 AM
                                Avoiding ping pongKlimax12/05/14 05:47 AM
                                  Avoiding ping pongEric Bron12/05/14 06:24 AM
                              Avoiding ping pongGabriele Svelto12/05/14 10:38 AM
                                Avoiding ping pongKonrad Schwarz12/07/14 02:28 PM
                                  Avoiding ping pongGabriele Svelto12/08/14 07:10 PM
                                    Avoiding ping pongKonrad Schwarz12/09/14 05:12 AM
                                      Avoiding ping pongGabriele Svelto12/09/14 07:31 AM
                                        Avoiding ping ponganon12/09/14 11:24 PM
                            Avoiding ping pongGabriele Svelto12/05/14 10:17 AM
                              Avoiding ping pongEric Bron12/05/14 10:32 AM
                                Avoiding ping pongGabriele Svelto12/05/14 12:45 PM
                                  Avoiding ping pongEric Bron12/06/14 02:20 AM
                                    Avoiding ping pongnksingh12/06/14 03:42 AM
                                      Avoiding ping pongEric Bron12/06/14 04:04 AM
                                        Avoiding ping pongGiGNiC12/06/14 06:27 AM
                                          Avoiding ping pongEric Bron nli12/06/14 06:44 AM
                                          Avoiding ping pongEric Bron12/06/14 07:07 AM
                                            Avoiding ping pongnksingh12/07/14 04:06 PM
                                              Avoiding ping pongEric Bron12/08/14 04:17 AM
                                                Avoiding ping pongGiGNiC12/08/14 11:53 AM
                                                Avoiding ping pongnksingh12/08/14 05:53 PM
                                                  Avoiding ping pongEric Bron12/09/14 01:33 AM
                                    Avoiding ping pongdmsc12/06/14 04:12 AM
                                      Avoiding ping pongEric Bron12/06/14 04:25 AM
                                        Avoiding ping pongKlimax12/06/14 05:49 AM
                                          Avoiding ping pongrwessel12/07/14 02:34 AM
                                        Avoiding ping pongdmsc12/06/14 07:39 AM
                                        Avoiding ping pongKonrad Schwarz12/07/14 02:37 PM
                                          Avoiding ping pongMichael S12/07/14 04:37 PM
                                            Avoiding ping pongKonrad Schwarz12/08/14 04:35 AM
                          Avoiding ping pongKonrad Schwarz12/05/14 03:30 AM
                        Avoiding ping pongLinus Torvalds12/05/14 12:58 PM
                          Avoiding ping pongEric Bron12/06/14 02:42 AM
                            Avoiding ping pongnksingh12/06/14 03:51 AM
                              Avoiding ping pongEric Bron12/06/14 04:08 AM
                            Avoiding ping pongLinus Torvalds12/06/14 01:25 PM
                              Avoiding ping pongnksingh12/07/14 03:26 PM
                                Avoiding ping pongEric Bron12/08/14 04:35 AM
                                  Avoiding ping pongBrett12/08/14 10:00 AM
                                    Avoiding ping pongEric Bron12/08/14 10:48 AM
                                    Avoiding ping pongrwessel12/08/14 12:52 PM
                                      Avoiding ping pongBrett12/08/14 01:58 PM
                                      Avoiding ping pongDoug S12/08/14 02:04 PM
                              Avoiding ping pongJouni Osmala12/08/14 02:45 AM
                                Avoiding ping ponganon12/08/14 05:44 AM
                                  Avoiding ping pongJouni Osmala12/08/14 01:10 PM
                                    Avoiding ping pongLinus Torvalds12/08/14 01:34 PM
                                      Avoiding ping pongJouni Osmala12/08/14 03:47 PM
                                        Avoiding ping pongLinus Torvalds12/08/14 08:08 PM
                                          Avoiding ping pongGabriele Svelto12/09/14 07:48 AM
                                            Avoiding ping pongMaynard Handley12/09/14 11:41 AM
                                              Avoiding ping pongPatrick Chase12/09/14 01:06 PM
                                              Avoiding ping pongGabriele Svelto12/09/14 01:52 PM
                                                Avoiding ping pongPatrick Chase12/09/14 02:08 PM
                                            Why read RWT or Reddit when you can get journalists to do it for you?Rob Thorpe01/02/15 08:20 AM
                                              Why read RWT or Reddit when you can get journalists to do it for you?juanrga01/02/15 11:21 AM
                                                Why read RWT or Reddit when you can get journalists to do it for you?EduardoS01/02/15 11:37 AM
                                                  Why read RWT or Reddit when you can get journalists to do it for you?juanrga01/03/15 12:00 PM
                                                Why read RWT or Reddit when you can get journalists to do it for you?Eric Bron nli01/02/15 02:28 PM
                                                  Why read RWT or Reddit when you can get journalists to do it for you?juanrga01/03/15 12:02 PM
                                                    Why read RWT or Reddit when you can get journalists to do it for you?Michael S01/03/15 12:36 PM
                                                      Why read RWT or Reddit when you can get journalists to do it for you?juanrga01/03/15 01:11 PM
                                                        Why read RWT or Reddit when you can get journalists to do it for you?Michael S01/03/15 01:30 PM
                                                          Why read RWT or Reddit when you can get journalists to do it for you?Eric Bron01/03/15 02:57 PM
                                                            KNL cacheDavid Kanter01/03/15 07:36 PM
                                                              KNL cacheEric Bron01/04/15 03:34 AM
                                                                KNL cacheMichael S01/04/15 04:11 AM
                                                                  KNL cacheEric Bron01/04/15 04:57 AM
                                                                    KNL cacheMichael S01/04/15 05:21 AM
                                                                      KNL cacheEric Bron01/04/15 05:58 AM
                                                          Why read RWT or Reddit when you can get journalists to do it for you?juanrga01/07/15 05:47 AM
                                                            Why read RWT or Reddit when you can get journalists to do it for you?Michael S01/07/15 08:27 AM
                                                              Manycores vs multicoresjuanrga01/10/15 04:10 PM
                                                                Manycores vs multicoresAaron Spink01/10/15 05:32 PM
                                                                  Manycores vs multicoresjuanrga01/10/15 06:32 PM
                                                                    Manycores vs multicoresExophase01/10/15 06:49 PM
                                                                      Manycores vs multicoresjuanrga01/10/15 08:21 PM
                                                                        Manycores vs multicoresExophase01/10/15 08:51 PM
                                                                        Manycores vs multicoresAaron Spink01/10/15 09:03 PM
                                                                    Manycores vs multicoresAaron Spink01/10/15 07:21 PM
                                                                      Manycores vs multicoresjuanrga01/10/15 08:25 PM
                                                                        Manycores vs multicoresAaron Spink01/10/15 09:11 PM
                                                                          Manycores vs multicoresJouni Osmala01/11/15 04:50 AM
                                                                            Manycores vs multicoresjuanrga01/11/15 08:58 AM
                                                                            Manycores vs multicorescoppice01/12/15 10:01 PM
                                                                              Manycores vs multicoresJouni Osmala01/13/15 04:38 AM
                                                                        Manycores vs multicoresanon01/11/15 03:19 AM
                                                                      Manycores vs multicoresMichael S01/11/15 05:44 AM
                                                                        Manycores vs multicoresAaron Spink01/11/15 05:55 PM
                                                                          Manycores vs multicoresMichael S01/12/15 04:41 AM
                                                                            Manycores vs multicoresEric Bron01/12/15 06:29 AM
                                                                              Manycores vs multicoresEric Bron01/12/15 06:30 AM
                                                        Why read RWT or Reddit when you can get journalists to do it for you?Eric Bron01/03/15 02:54 PM
                                                          Why read RWT or Reddit when you can get journalists to do it for you?juanrga01/07/15 05:48 AM
                                                            Why read RWT or Reddit when you can get journalists to do it for you?Eric Bron01/07/15 07:41 AM
                                                              Manycores vs multicoresjuanrga01/10/15 04:14 PM
                                                    Why read RWT or Reddit when you can get journalists to do it for you?Eric Bron01/03/15 02:42 PM
                                                      Why read RWT or Reddit when you can get journalists to do it for you?juanrga01/07/15 06:03 AM
                                                        Why read RWT or Reddit when you can get journalists to do it for you?Eric Bron01/07/15 07:45 AM
                                                        Why read RWT or Reddit when you can get journalists to do it for you?Linus Torvalds01/08/15 03:09 PM
                                                          Pink unicorns for salejuanrga01/10/15 05:09 PM
                                                        Intentionally picking a competitors slow part is cheating ...Mark Roulo01/08/15 06:37 PM
                                                          Intentionally picking a competitors slow part is cheating ...coppice01/08/15 11:38 PM
                                                            Intentionally picking a competitors slow part is cheating ...Mark Roulo01/09/15 09:13 AM
                                                              Intentionally picking a competitors slow part is cheating ...Anon01/10/15 02:00 AM
                                                              Intentionally picking a competitors slow part is cheating ...David Hess01/11/15 01:03 PM
                                                            Intentionally picking a competitors slow part is cheating ...someone01/09/15 10:31 AM
                                                              Intentionally picking a competitors slow part is cheating ...coppice01/12/15 09:45 PM
                                                                Intentionally picking a competitors slow part is cheating ...coppice01/12/15 09:47 PM
                                                                  Intentionally picking a competitors slow part is cheating ...Michael S01/13/15 07:53 AM
                                                                    Intentionally picking a competitors slow part is cheating ...coppice01/13/15 09:44 AM
                                                                      Intentionally picking a competitors slow part is cheating ...Michael S01/13/15 10:01 AM
                                                                        Intentionally picking a competitors slow part is cheating ...coppice01/13/15 08:35 PM
                                                                      Core sizesjuanrga01/13/15 12:28 PM
                                                          NVIDIA'S FIRST CPU IS A WINNER (Linley Gwennap)juanrga01/10/15 04:34 PM
                                                        Why read RWT or Reddit when you can get journalists to do it for you?Patrick Chase01/08/15 07:02 PM
                                                        Why read RWT or Reddit when you can get journalists to do it for you?coppice01/08/15 10:18 PM
                                                          Why read RWT or Reddit when you can get journalists to do it for you?Patrick Chase01/09/15 11:54 AM
                                                            Why read RWT or Reddit when you can get journalists to do it for you?Mark Roulo01/09/15 12:59 PM
                                                              Why read RWT or Reddit when you can get journalists to do it for you?Patrick Chase01/09/15 03:20 PM
                                                                Why read RWT or Reddit when you can get journalists to do it for you?Eric Bron01/09/15 03:30 PM
                                                            Alternatives to OOOE (again)juanrga01/10/15 04:50 PM
                                                              Alternatives to OOOE (again)David Kanter01/11/15 12:10 AM
                                                                Alternatives to OOOE (again)juanrga01/11/15 08:30 AM
                                                            Why read RWT or Reddit when you can get journalists to do it for you?Gabriele Svelto01/11/15 12:53 AM
                                              Why read RWT or Reddit when you can get journalists to do it for you?Fake Linus Torvalds01/03/15 12:14 PM
                                                Why read RWT or Reddit when you can get journalists to do it for you?Rob Thorpe01/03/15 08:25 PM
                                          Avoiding ping pongMaynard Handley12/09/14 11:33 AM
                                            Avoiding ping pongPatrick Chase12/09/14 01:54 PM
                                              Avoiding ping pongMaynard Handley12/09/14 06:56 PM
                                      Avoiding ping pongSalvatore De Dominicis12/09/14 08:51 AM
                                        Avoiding ping pongPatrick Chase12/09/14 02:00 PM
                                      Avoiding ping pongook12/11/14 03:31 AM
                                      Avoiding ping pongArt Scott12/19/14 10:19 PM
                                        Avoiding ping pongEric Bron nli12/20/14 04:05 AM
                                      What about specialization?Troll?01/02/15 07:55 AM
                                        What about specialization?Ungo01/04/15 03:27 PM
                                      Avoiding ping pongfewwef01/05/15 08:16 PM
                                      Avoiding ping pongV.Krishn01/08/15 06:11 AM
                                    Avoiding ping pongGabriele Svelto12/08/14 07:32 PM
                                    Avoiding ping ponganon12/08/14 11:37 PM
                            Avoiding ping pongKonrad Schwarz12/10/14 06:23 AM
                              Avoiding ping pongLinus Torvalds12/10/14 11:56 AM
                          Object reference lockingDavid W12/08/14 11:36 PM
                            Object reference lockingPatrick Chase12/09/14 04:52 PM
                              Object reference lockingDavid W12/11/14 05:18 AM
                    ISA != interface for "most programmers"Paul A. Clayton12/04/14 03:34 PM
                      ISA != interface for "most programmers"rwessel12/04/14 07:50 PM
                  Interesting! (exporting hot lines/cache-aware ISA); "Please sir, I want some more" (NT)Paul A. Clayton12/04/14 02:26 PM
                  Avoiding ping pongMichael S12/06/14 03:48 PM
          ARMv8 getting atomic operationsLinus Torvalds12/04/14 12:05 PM
            LL/SC idiom recognition is not admitting RMW superiorityPaul A. Clayton12/04/14 02:34 PM
            ARMv8 getting atomic operationsanon12/04/14 10:17 PM
    ARMv8 getting atomic operationsPatrick Chase12/03/14 12:09 PM
  limited ordernksingh12/04/14 10:17 PM
    I didn't understand this either. (NT)Konrad Schwarz12/04/14 10:32 PM
    limited orderdmcq12/05/14 02:13 AM
    limited orderbakaneko12/05/14 09:11 AM
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