Avoiding ping pong

By: Linus Torvalds (torvalds.delete@this.linux-foundation.org), December 8, 2014 7:08 pm
Room: Moderated Discussions
Jouni Osmala (josmala.delete@this.cc.hut.fi) on December 8, 2014 3:47 pm wrote:
>
> There is enough scaling left to turn somewhat better than current high end xeons to client
> CPU:s

Maybe. And probably not. Given the choice between 16 cores and 4, I suspect most people will take 4, and prefer more cache, graphics, and integrated networking etc.

> Especially when stacked dram becomes standard and L3 cache becomes redundant due to
> lower latency on main memory, and there would be enormous bandwidth available to CPU:s.

Again, unlikely. Especially with all those cores. You want the L3 as a synchronization point for all your theoretical parallel programs that would otherwise have totally unacceptable synchronization overheads.

Stacked RAM may help throughput, but it won't be running at CPU frequencies, and latency of communication between cores is pretty primary.

Of course, that all assumes that the parallel solutions exist at all, which is still an open question (aka "not solved in the last few decades, probably not solvable at all")

> On arm front highly parallel world may become reality

Ok, now your'e just veering off into la-la-land.

Are you talking about that Cavium chip? The one that will be completely useless for general-purpose loads? That one?

Yeah.

> on Intel world its more like having
> 16 core client where each core is slightly MORE powerful than current core , and servers
> probably have 60 of same cores but having lower base frequency and higher power budget.

I can imagine people actually using 60 cores in the server space, yes. I don't think we'll necessarily see it happen on a huge scale, though. It's probably more effective to make bigger caches and integrate more of the IO on the server side too.

On the client side, there are certainly still workstation loads etc that can use 16 cores, and I guess graphics professionals will be able to do their photoshop and video editing faster. But that's a pretty small market in the big picture. There's a reason why desktops are actually shrinking.

So the bulk of the market is probably more in that "four cores and lots of integration, and make it cheap and low-power" market.

But hey, predicting is hard. Especially the future. We'll see.

> I'm talking about diminishing return's on going beyond where those complex OoO
> cores are right now. And there is enough scaling left to go for 16+ cores of
> similar complexity of current high end cores with added wider vector unit.

.. and you are then completely ignoring the diminishing returns of parallelism. There are serious issues going past scaling past a handful or cores. And it's expensive as hell.

Some things are cheap and easy. But those are done already. Building stuff in parallel? Trivial - except even there people tend to have build tools and Makefiles etc that make it not work that well in many cases. So even something really simple like a software workstation often doesn't scale that well (I'm happy to say that the kernel build scales exceptionally well, but most projects don't have tens of thousands of files and lots of effort on the build system.

The "more parallelism" people aren't new. This has been debated for decades, and the extreme parallelism people have been wrong for decades. I don't see anything that has really changed things. And if anything, scaling limits will take some of their arguments away.

I work on a project where we're doing extreme scaling. We're proud of it. But I also see the pain. For us, it makes sense to spend the effort. I don't see that being true in 99% of all cases.

Linus
< Previous Post in ThreadNext Post in Thread >
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
Reply to this Topic
Name:
Email:
Topic:
Body: No Text
How do you spell green?