No. Mill does not get the hit because it does not get the benefit even when correctly predicted.

By: anon (anon.delete@this.anon.com), January 2, 2019 2:05 am
Room: Moderated Discussions
Brett (ggtgp.delete@this.yahoo.com) on January 2, 2019 12:15 am wrote:
> Heikki Kultala (heikki.kultala.delete@this.tuni.fi) on January 1, 2019 11:29 pm wrote:
> > Brett (ggtgp.delete@this.yahoo.com) on January 1, 2019 6:39 pm wrote:
> > > Travis Downs (travis.downs.delete@this.gmail.com) on December 30, 2018 8:48 pm wrote:
> > > > Brett (ggtgp.delete@this.yahoo.com) on December 30, 2018 7:51 pm wrote:
> > > >
> > > > > Before I finished writing the above Micro Threading post I figured a modern OoO probably does most of
> > > > > what I am proposing.
> > > >
> > > > They don't.
> > > >
> > > > > After the first branch miss the instruction que quickly fills enough and there is
> > > > > enough work to do that it does not need to predict the branch, and can wait for the branch value.
> > > > >
> > > > > A simple benchmark could test if the CPU does slow down by three times on a data driven branch.
> > > >
> > > > Generally they do (slow down). The basic problem is that there isn't a lot of work to do because
> > > > the CPU is spending all of its time recovering from the mispredict. Only work from before the
> > > > mispredict can keep executing. Consider your hypothetical 6-wide CPU with 12 cycle bubble due
> > > > to branch mispredict, executing a loop with 24 or 12 instructions (50% of the time each).
> > > >
> > > > Every 2 iterations you have 36 instructions to execute, taking 6 cycles with infinite ILP. However, the CPU
> > > > can't issue any instructions for 12 cycles so 12 cycles
> > > > (half speed) is a hard upper bound on the performance
> > > > even for a CPU with infinitely wide decode that can decode at least the next 36 instructions in zero cycles
> > > > and resolves the next mispredicted branch in the very first cycle after execution resumes.
> > >
> > > Yes all work must be thrown away on a branch miss and so I was wrong, you get do get a three times slowdown.
> > >
> > > With the Mill arch a branch is much like a call, you could just throw away the result and
> > > computations on branch miss. As you get fresh registers on a Mill belt call there is no
> > > register aliasing issue that forces you to throw away work beyond the branch return.
> >
> > Mill does not perform speculative [b]execution[/b]. It only performs
> > branch prediction and speculative fetching and decoding of code.
>
> Yet.
> The Mill team has not shipped v1.0, this is more a possible v2.0 feature.
>
> > So, on mill, there [b]never is that parallelism over multiple basic blocks even when the
> > branch is [b]correctly predicted[/b]. Unless you have the magic unicorn compiler.
>
> I already pointed out that tagging leaf branches is a trivial compiler change.
> No magic unicorn compiler needed.
>
> > > So Mill could get this three times speedup on poorly predicted data driven code.
> >
> > No. It's much worse than OoOE even with [b]correctly predicted[/b] branches.
> >
> > > Also explains Mill unusual super width and huge operation count per
> > > cycle, which people think are pointless, stupid and wasteful.
> >
> > No, it does not. Those are left unused because magic unicorn compiler is needed to interleave
> > the instructions from multiple basic blocks in anything else but very simple loops.
>
> The Mill team is modifying a compiler, but that is because of design suitability issues, not unicorns.
>
> This is not Itanic, which was always a pack of lies, from every angle you look at the problem.

I don't think it was always a pack of lies. I think it was sold to Intel management by some very smart technical people who sincerely thought it was a good idea, and with actual models and data and projections to support them.

They may have been flawed models, optimistic projections, unconscious bias, etc., but I would not call it a pack of lies from the beginning. Actually I would put it in quite a similar position as Mill, if you subtract the vast amounts of money Intel/HP sunk into it.

> The Mill team does not have billions to chase rainbows, which
> is the most generous thing you can say Itanic was doing.
>
> > > This would make Mill competitive with OoO, which everyone here thinks is impossible, to the point
> > > they think Mill is a scam and a joke. People may be surprised and end up with egg on their faces.
> > >
> > > As a pro Mill person this would be yet another victory for me. ;)
> >
> > No, it does not.
>
> Time will tell, I can wait.
>

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TopicPosted ByDate
Independent micro threadsBrett2018/12/30 12:55 PM
  Independent micro threadsTravis Downs2018/12/30 03:18 PM
    Independent micro threadsBrett2018/12/30 06:16 PM
      Independent micro threadsTravis Downs2018/12/30 06:34 PM
        Independent micro threadsBrett2018/12/30 06:48 PM
          Independent micro threadsTravis Downs2018/12/30 08:06 PM
            Independent micro threadsBrett2018/12/30 09:57 PM
              Independent micro threadsTravis Downs2018/12/30 11:42 PM
                Independent micro threadsBrett2019/01/01 06:02 PM
                  Independent micro threadsMichael S2019/01/02 01:01 AM
                    Independent micro threadsMaynard Handley2019/01/02 02:29 PM
              Independent micro threadsMontaray Jack2019/01/01 01:12 AM
  Independent micro threadsanon2018/12/30 03:34 PM
  Independent micro threadsPaul A. Clayton2018/12/30 04:15 PM
  Independent micro threadsDavid Hess2018/12/30 05:47 PM
    Independent micro threadsDomaldel2018/12/30 06:06 PM
      Independent micro threadsDavid Hess2018/12/30 06:26 PM
        Independent micro threadsDoug S2018/12/31 09:26 AM
          Independent micro threadsDavid Hess2018/12/31 08:32 PM
            Independent micro threadsDoug S2018/12/31 11:40 PM
              Independent micro threadsDavid Hess2019/01/01 10:41 AM
            Overcomming thermal limits of a high dencity 3D arcitecture (Formerly "Independent micro threads")Domaldel2018/12/31 11:40 PM
              Overcomming thermal limits of a high dencity 3D arcitecture (Formerly "Independent micro threads")Domaldel2018/12/31 11:44 PM
                Overcomming thermal limits of a high dencity 3D arcitecture (Formerly "Independent micro threads")Domaldel2018/12/31 11:49 PM
                  Overcomming thermal limits of a high dencity 3D arcitecture (Formerly "Independent micro threads")Domaldel2018/12/31 11:51 PM
              Overcomming thermal limits of a high dencity 3D arcitecture (Formerly "Independent micro threads")Simon Farnsworth2019/01/01 05:05 AM
                Overcomming thermal limits of a high dencity 3D arcitecture (Formerly "Independent micro threads")Domaldel2019/01/01 07:01 AM
                Overcomming thermal limits of a high dencity 3D arcitecture (Formerly "Independent micro threads")Maynard Handley2019/01/01 12:17 PM
                  Taking things to extremes.Domaldel2019/01/01 04:44 PM
                    Yes, I know, the forum is named *Real* World Tech, but I'm thinking that perhapsDomaldel2019/01/01 04:52 PM
                      Yes, I know, the forum is named *Real* World Tech, but I'm thinking that perhapsMontaray Jack2019/01/02 06:26 AM
                        Yes, I know, the forum is named *Real* World Tech, but I'm thinking that perhapsMontaray Jack2019/01/02 07:21 AM
                    Taking things to extremes.Maynard Handley2019/01/01 05:55 PM
                    Taking things to extremes.Kevin G2019/01/04 07:57 AM
              Overcomming thermal limits of a high dencity 3D arcitecture (Formerly "Independent micro threads")David Hess2019/01/01 10:36 AM
    Independent micro threadsTravis Downs2018/12/30 06:38 PM
    Independent micro threadsBrett2018/12/30 06:41 PM
  Independent micro threadsanon2018/12/30 07:20 PM
    Independent micro threadsBrett2018/12/30 07:51 PM
      Independent micro threadsTravis Downs2018/12/30 08:48 PM
        Mill and Independent micro threadsBrett2019/01/01 06:39 PM
          No. Mill does not get the hit because it does not get the benefit even when correctly predicted.Heikki Kultala2019/01/01 11:29 PM
            No. Mill does not get the hit because it does not get the benefit even when correctly predicted.Brett2019/01/02 12:15 AM
              No. Mill does not get the hit because it does not get the benefit even when correctly predicted.Heikki Kultala2019/01/02 01:22 AM
                No. Mill does not get the hit because it does not get the benefit even when correctly predicted.Brett2019/01/03 12:13 AM
                  "Leaf branch" is not a commonly used termHeikki Kultala2019/01/03 02:48 AM
                    "Leaf branch" is not a commonly used termBrett2019/01/03 03:35 AM
                      You lack parallelism than OoOE givesHeikki Kultala2019/01/03 06:38 AM
                        You lack parallelism than OoOE givesBrett2019/01/04 01:41 AM
                          You lack parallelism than OoOE givesBrett2019/01/04 03:10 PM
                            You lack parallelism than OoOE givesBrett2019/01/05 07:29 PM
                              Mill speculates, more parallelism than OoOE givesBrett2019/01/05 07:31 PM
                                Mill *is* a speculationEric Bron2019/01/06 04:04 AM
                                  Mill *is* a speculationMichael S2019/01/06 04:53 AM
                                    Mill *is* a speculationBrett2019/01/06 08:03 PM
                                  Mill *is* a speculationjuanrga2019/01/06 05:10 AM
                                    probably ~2 (NT)Michael S2019/01/06 05:51 AM
                                  Mill *is* a speculationBrett2019/01/06 12:18 PM
                                    Mill *is* a speculationEric Bron2019/01/06 02:36 PM
                                      Mill *is* a speculationBrett2019/01/06 07:47 PM
                                        Mill *is* a speculationJacob Marley2019/01/06 09:29 PM
                                          Mill *is* a speculationBrett2019/01/07 03:24 AM
                                            Mill *is* a speculationMichael S2019/01/07 04:23 AM
                                            Mill *is* a speculationEric Bron2019/01/07 04:36 AM
                                              Mill *is* a speculationBrett2019/01/07 02:40 PM
                                                Mill *is* a speculationEric Bron2019/01/07 04:32 PM
                                            Mill is something you don't understandHeikki Kultala2019/01/08 03:19 AM
                                              Mill is something you don't understandMichael S2019/01/08 06:44 AM
                                                Itanium and static vs dynamicHeikki Kultala2019/01/09 02:14 AM
                                                  Itanium and static vs dynamicPaul A. Clayton2019/01/09 07:51 AM
                                        Mill *is* a speculationEric Bron2019/01/07 04:27 AM
                                          Mill *is* a speculationEric Bron2019/01/07 05:23 AM
                                      Mill *is* a speculationanon2019/01/07 05:24 AM
                                        Mill *is* a speculationEric Bron2019/01/07 05:52 AM
                                          Mill *is* a speculationanon2019/01/07 07:36 AM
                                            Mill *is* a speculationEric Bron2019/01/07 08:20 AM
                                        Mill *is* a speculationjuanrga2019/01/07 09:22 AM
                                          Mill *is* a speculationanon2019/01/07 12:16 PM
                                        Mill *is* a speculationanon2019/01/07 08:46 PM
                                          Mill *is* a speculationanon2019/01/08 12:56 AM
                                            Mill *is* a speculationanon2019/01/08 02:39 AM
                                              Mill *is* a speculationMichael S2019/01/08 02:52 AM
                                                Mill *is* a speculationanon2019/01/08 09:10 PM
                                                  Wasted width not wasted work.Brett2019/01/09 10:44 AM
                                                    No such thing was declared. (NT)anon2019/01/09 02:41 PM
                                                    Very simple test for new uarch ideassomeone2019/01/10 06:03 AM
                                                      Very simple test for new uarch ideasdmcq2019/01/10 06:21 AM
                                                        Very simple test for new uarch ideasDoug S2019/01/10 09:01 AM
                                                          Very simple test for new uarch ideasDan Fay2019/01/10 12:13 PM
                                                      Very simple test for new uarch ideasanonymous22019/01/10 10:03 AM
                                                        Very simple test for new uarch ideasAlberto2019/01/10 10:32 AM
                                                      Very simple test for new uarch ideasEtienne2019/01/11 02:03 AM
                                                        Very simple test for new uarch ideasFoo_2019/01/11 03:31 AM
                                                          Very simple test for new uarch ideasEtienne2019/01/11 04:51 AM
                                                            Very simple test for new uarch ideasFoo_2019/01/11 04:53 AM
                                                              Very simple test for new uarch ideasdmcq2019/01/11 05:08 AM
                                                              Very simple test for new uarch ideasEtienne2019/01/11 05:13 AM
                                                                Very simple test for new uarch ideasFoo_2019/01/11 05:54 AM
                                                                  Very simple test for new uarch ideasEtienne2019/01/11 06:32 AM
                                                                    Very simple test for new uarch ideasBrett2019/01/11 09:25 AM
                                                                      Very simple test for new uarch ideasMegol2019/01/12 05:29 AM
                                                                        Very simple test for new uarch ideasMichael S2019/01/12 08:21 AM
                                                                          Word salad AI fundamentaliy brokenBrett2019/01/12 12:59 PM
                                                                          Very simple test for new uarch ideasMegol2019/01/13 10:51 AM
                                              Mill *is* a speculationanon2019/01/08 07:50 AM
                                                Mill *is* a speculationEric Bron2019/01/08 08:03 AM
                                                  Mill *is* a speculationanon2019/01/08 08:21 AM
                      "Leaf branch" is not a commonly used termMichael S2019/01/03 06:57 AM
                        "Leaf branch" is not a commonly used termBrett2019/01/04 02:29 AM
                  Calls are not needed for speculation for mill if there are no side effect,and dont help if there areHeikki Kultala2019/01/08 03:28 AM
              No. Mill does not get the hit because it does not get the benefit even when correctly predicted.anon2019/01/02 02:05 AM
              No. Mill does not get the hit because it does not get the benefit even when correctly predicted.Doug S2019/01/02 10:38 AM
                No. Mill does not get the hit because it does not get the benefit even when correctly predicted.rwessel2019/01/02 04:53 PM
                  No. Mill does not get the hit because it does not get the benefit even when correctly predicted.anon2019/01/02 07:56 PM
                    itanicBrett2019/01/02 11:41 PM
                      itanicanon2019/01/03 02:12 AM
                      itanicDavid Hess2019/01/03 07:06 AM
                    No. Mill does not get the hit because it does not get the benefit even when correctly predicted.rwessel2019/01/03 08:18 AM
                      No. Mill does not get the hit because it does not get the benefit even when correctly predicted.anon2019/01/04 04:25 AM
                    Itanium could have been RISC or CISC - same outcomesomeone2019/01/04 06:45 AM
                      Itanium could have been RISC or CISC - same outcomeDoug S2019/01/04 11:39 AM
                        Itanium could have been RISC or CISC - same outcomeJan Olšan2019/01/04 12:58 PM
                          "fluffyRISC" has a namevvid2019/01/04 02:48 PM
                        Itanium could have been RISC or CISC - same outcomeBrett2019/01/04 02:43 PM
                      Itanium could have been RISC or CISC - same outcomeanonymou52019/01/04 11:41 AM
                  No. Mill does not get the hit because it does not get the benefit even when correctly predicted.David Hess2019/01/03 07:15 AM
                No. Mill does not get the hit because it does not get the benefit even when correctly predicted.Maynard Handley2019/01/03 11:24 AM
                  No. Mill does not get the hit because it does not get the benefit even when correctly predicted.Maynard Handley2019/01/03 11:27 AM
                    No. Mill does not get the hit because it does not get the benefit even when correctly predicted.dmcq2019/01/04 12:59 AM
                  EPIC target marketsFoo_2019/01/04 05:29 AM
                    EPIC target marketsDoug S2019/01/04 11:42 AM
                      Lack of future visionDoug S2019/01/04 11:57 AM
                        Lack of future visionBrett2019/01/04 01:59 PM
                          Lack of future visionDoug S2019/01/04 03:25 PM
                            Lack of future visionBrett2019/01/04 04:18 PM
                              Lack of future visionDoug S2019/01/04 11:47 PM
                                Lack of future visionBrett2019/01/05 01:06 PM
                                  Lack of future visiondmcq2019/01/05 01:22 PM
                                  Lack of future visionanon2019/01/05 02:01 PM
                                    Lack of future visionMichael S2019/01/05 03:18 PM
                                      Lack of future visionanon2019/01/05 05:14 PM
                                        Lack of future visionMichael S2019/01/06 01:01 AM
                                          Lack of future visionanon2019/01/06 02:23 AM
                                          Mitch Alsup's MY66000 uses IF-like predication (I think) (NT)Paul A. Clayton2019/01/06 03:54 PM
                                            ??? (NT)Michael S2019/01/07 04:25 AM
                                            88K ? (NT)anonymous22019/01/07 03:20 PM
                                          Modestly expanded response: MY66000 predicate shadowPaul A. Clayton2019/01/07 10:53 AM
                      Thanks for the correction (NT)Foo_2019/01/04 03:31 PM
              No. Mill does not get the hit because it does not get the benefit even when correctly predicted.sdrc2019/01/04 06:36 AM
          Mill and Independent micro threadsMichael S2019/01/02 01:32 AM
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