Apple loses a lot by not having turbo and SMT

By: Dummond D. Slow (mental.delete@this.protozoa.us), November 19, 2020 4:10 pm
Room: Moderated Discussions
Maynard Handley (name99.delete@this.name99.org) on November 19, 2020 9:13 am wrote:
> Adrian (a.delete@this.acm.org) on November 19, 2020 1:50 am wrote:
> > Maynard Handley (name99.delete@this.name99.org) on November 18, 2020 4:46 pm wrote:
> > > Dummond D. Slow (mental.delete@this.protozoa.us) on November 18, 2020 3:17 pm wrote:
> > > > Jon Masters (jcm.delete@this.jonmasters.org) on November 18, 2020 11:46 am wrote:
> > > > > Dummond D. Slow (mental.delete@this.protozoa.us) on November 17, 2020 11:18 am wrote:
> > > > >
> > > > > > It's simple: SMT. Had Apple implemented it, it would run away in Cinebench.
> > > > > > Lesson to the people saying it's a pointless/stupid/doomed feature.
> > > > > > Seems Renoir is able to bridge its "worse single-thread" and "worse
> > > > > > manufacturing node" disadvantage pretty much thanks to SMT.
> > > > > >
> > > > > > Which also tells you where the biggest threat from Apple is. It pretty much caught
> > > > > > up with state of the art x86's single core performance AND has process advantage.
> > > > > > It could shoot ahead in performance in two areas if it chose to:
> > > > > > 1) SMT as discussed. Not having SMT leaves massive multithread performance
> > > > > > gains (end energy efficiency gains, more importantly) on the table.
> > > > >
> > > > > SMT is a *terrible* idea for new designs. Sure, it gets you performance uplift, but it comes
> > > > > at a cost, particularly in terms of side-channel exposure. That is a game of whack-a-mole that
> > > > > doesn't end any time in the near future. Real cores that can be fed properly give you more
> > > > > deterministic performance without all of the other downsides from sharing resources.
> > > > >
> > > > > Jon.
> > > > >
> > > >
> > > > Everything has side channels, I stopped counting and stopped reporting on new attacks described. So I
> > > > think it makes no sense to ditch SMT on the grounds of side channel vulns because there is 10-20x more
> > > > in other parts of the CPU, discovered each year. You just sacrifice something good and then you find
> > > > it didn't help in anything. The solution for that is to handle it in CPU scheduling (don't give two threads
> > > > from one core to different VMs on server and so on + whatever more is needed for security).
> > > > You don't want shared L3 cache or multicore CPUs being abandoned either, do you?
> > >
> > > So now you're starting to concede my point.
> > > If you're going to do SMT right, you don't share threads between unrelated entities.
> > > That means
> > > (a) you don't have to waste any effort worrying about security
> > > (b) you don't have to worry at all about fairness
> > >
> > > But then if the entities are related, why do you need the OS (except to do the context swapping correctly).
> > > Provide user-level primitives to launch, kill, and synchronize with the other thread. At which point
> > > - the two threads are closely related, so resource contention is PROBABLY not an issue and
> > > - the app is in control, so to the extent that contention is an
> > > issue, the app can choose not to launch a companion thread
> > >
> > > There is a right way and a wrong way of doing things. The wrong way, in this case, is treating
> > > SMT as a fake core, rather than something like a "co-routine acceleration engine".
> >
> >
> >
> > Yes, I completely agree that the method to extract maximum performance from SMT is to not
> > treat "SMT as a fake core", but as 'something like a "co-routine acceleration engine"'.
> >
> >
> > Nevertheless, there are some kinds of applications, not many, but quite
> > important, where using the SMT threads as fake cores works very well.
> >
> > These applications have threads that do many I/O or large memory access operations
> > and the threads are well decorrelated in their access patterns.
> >
> > The typical examples are the compilation of large projects, using many concurrent
> > threads and database servers that serve many concurrent requests.
> >
> >
> > These applications, where SMT fake cores are OK, rely on randomness
> > to increase the average occupancy of the execution units.
> >
> > Optimized applications, which use SMT as a "co-routine acceleration engine", can achieve
> > much better occupancies, while other applications, whose threads are correlated in the
> > needs for resources, achieve worse performance with SMT, due to contention.
>
> At this point we hit the constant running through every aspect of this discussion:
> - do you make the one-time effort to do a job properly, or do you just half-ass it this
> year, then half-ass it again next year, then half-ass it again the following year?
>
> Yes, you can half-ass SMT. Just like you can half-ass your CPU design for ten years.
> It appears that 90% of the people on this forum prefer to half-ass everything. Thank god there
> are a few companies like ARM and Apple that don't think this way. I just want to ensure that same
> level of not "half-assing, just because that's what everyone else did" applies to Apple's implementation
> of SMT (and, in an ideal world, to ARM's canonical version, when that comes).
>

And that "half-assed" narrative is based on ...?

>
> To add to the list of ARM SMT implementations (using the half-assed worldview)
> for people really interested in this, look at the MIPS MT ASE:
> https://s3-eu-west-1.amazonaws.com/downloads-mips/documents/MD00452-2B-MIPSMT-WHP-01.02.pdf
>
> MIPS got a lot of this wrong (in particular they too were in love with that eternal darling of the young computer
> engineer, the promise of virtualization) but they at least approached closer to ideal than anyone else;
> with the *possibility* that what they were providing were not
> in fact vCPUs, and with some adequate user-level instructions.

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TopicPosted ByDate
1st round of M1 GPU benchmarksMaynard Handley2020/11/16 01:46 PM
  1st round of M1 GPU benchmarksAdrian2020/11/16 02:02 PM
    1st round of M1 GPU benchmarksI_vs2020/11/17 02:18 AM
  1st round of M1 GPU benchmarksRType2020/11/16 02:06 PM
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      And the NZ'ers are first to deliver cinebench scoresMaynard Handley2020/11/16 03:58 PM
        And the NZ'ers are first to deliver cinebench scoresWill2020/11/16 04:30 PM
          re: "scaling"Dummond D. Slow2020/11/16 05:06 PM
            re: "scaling"Maynard Handley2020/11/16 05:29 PM
              re: "scaling"Dummond D. Slow2020/11/16 05:51 PM
                re: "scaling"Maynard Handley2020/11/16 06:51 PM
                  re: "scaling"Dummond D. Slow2020/11/16 07:22 PM
                    re: "scaling"Maynard Handley2020/11/16 07:23 PM
                      re: "scaling"Maynard Handley2020/11/16 07:27 PM
                        re: "scaling"Dummond D. Slow2020/11/16 07:37 PM
                          re: "scaling"Chester2020/11/16 09:25 PM
                          Actual power consumption values.Dummond D. Slow2020/11/17 08:05 AM
                    re: "scaling"Doug S2020/11/17 11:25 AM
                      Apple loses a lot by not having turbo and SMTDummond D. Slow2020/11/17 12:18 PM
                        Apple loses a lot by not having turbo and SMTDoug S2020/11/17 01:21 PM
                          Apple loses a lot by not having turbo and SMTblaine2020/11/19 06:18 PM
                            Apple loses a lot by not having turbo and SMTDummond D. Slow2020/11/19 06:31 PM
                        Apple loses a lot by not having turbo and SMTTJ2020/11/18 02:10 AM
                          Cinebench is NOT a representation of average workloadsAndrei F2020/11/18 06:21 AM
                            SPEC is NOT a representation of average workloadsChester2020/11/18 08:02 AM
                              SPEC is NOT a representation of average workloadsDummond D. Slow2020/11/18 08:17 AM
                                SPEC is NOT a representation of average workloadsnone2020/11/18 09:18 AM
                                  x264 without SIMD is nonsenseDummond D. Slow2020/11/18 09:31 AM
                                  SPEC is NOT a representation of average workloadsMaynard Handley2020/11/18 10:13 AM
                                    SPEC is NOT a representation of average workloadsDummond D. Slow2020/11/18 10:21 AM
                                      SPEC is NOT a representation of average workloadsWilco2020/11/18 10:42 AM
                                        role of hand-optimized assembly in multimedia encodersDummond D. Slow2020/11/18 12:06 PM
                                          role of hand-optimized assembly in multimedia encodersdifferent anon2020/11/18 02:27 PM
                                            role of hand-optimized assembly in multimedia encodersDummond D. Slow2020/11/18 03:47 PM
                                              role of hand-optimized assembly in multimedia encodersDummond D. Slow2021/05/18 01:29 PM
                                          role of hand-optimized assembly in multimedia encodersRichardC2020/11/18 04:42 PM
                                          role of hand-optimized assembly in multimedia encodersnone2020/11/19 08:17 AM
                                      SPEC is NOT a representation of average workloadsnone2020/11/18 11:14 AM
                                        SPEC is NOT a representation of average workloadsDummond D. Slow2020/11/18 12:17 PM
                                      SPEC is NOT a representation of average workloadsMaynard Handley2020/11/18 12:03 PM
                                        SPEC is NOT a representation of average workloadsDummond D. Slow2020/11/18 12:25 PM
                                          SPEC is NOT a representation of average workloadsMaynard Handley2020/11/18 01:03 PM
                                            SPEC is NOT a representation of average workloadsDummond D. Slow2020/11/18 03:57 PM
                                              SPEC is NOT a representation of average workloadsMaynard Handley2020/11/18 05:36 PM
                                                SPEC is NOT a representation of average workloadsDummond D. Slow2020/11/18 05:50 PM
                                                  SPEC is NOT a representation of average workloadsDoug S2020/11/19 10:13 AM
                                                    SPEC is NOT a representation of average workloads-.-2020/11/19 03:34 PM
                                                    SPEC is NOT a representation of average workloadsDummond D. Slow2020/11/19 03:35 PM
                                              SPEC is NOT a representation of average workloadsEtienne Lorrain2020/11/19 05:04 AM
                                                SPEC is NOT a representation of average workloadsDummond D. Slow2020/11/19 06:58 AM
                                SPEC is NOT a representation of average workloadsChester2020/11/18 03:06 PM
                                  about bitratesDummond D. Slow2020/11/18 04:04 PM
                                    about bitratesChester2020/11/19 03:45 PM
                                  SPEC is NOT a representation of average workloadsOok2020/11/18 04:05 PM
                                    SPEC is NOT a representation of average workloadsDummond D. Slow2020/11/18 04:21 PM
                                  SPEC is NOT a representation of average workloadsNoSpammer2020/11/19 07:48 AM
                              SPEC is NOT a representation of average workloadsAndrei F2020/11/18 08:44 AM
                                SPEC is NOT a representation of average workloadsDummond D. Slow2020/11/18 08:48 AM
                                  SPEC is NOT a representation of average workloadsAdrian2020/11/18 09:15 AM
                                    SPEC is NOT a representation of average workloadsDummond D. Slow2020/11/18 09:41 AM
                                      SPEC is NOT a representation of average workloadsAdrian2020/11/18 10:04 AM
                                        SPEC is NOT a representation of average workloadsDummond D. Slow2020/11/18 10:32 AM
                                          SPEC is NOT a representation of average workloadsAdrian2020/11/18 11:26 AM
                                    SPEC is NOT a representation of average workloadsMaynard Handley2020/11/18 10:22 AM
                                      SPEC is NOT a representation of average workloadsAdrian2020/11/18 11:28 AM
                                  SPEC is NOT a representation of average workloadsAndrei F2020/11/18 09:34 AM
                                    SPEC is NOT a representation of average workloadsDummond D. Slow2020/11/18 10:00 AM
                                    SPEC is NOT a representation of average workloadsChester2020/11/18 03:18 PM
                                    SPEC is NOT a representation of average workloadsJukka Larja2020/11/20 09:03 AM
                                SPEC is NOT a representation of average workloadsChester2020/11/18 03:13 PM
                              SPEC is NOT a representation of average workloadsnone2020/11/18 09:07 AM
                                SPEC is NOT a representation of average workloadsMichael S2020/11/18 02:33 PM
                                  Interesting, thanks! (NT)none2020/11/19 08:03 AM
                            Cinebench is NOT a representation of average workloadsrwessel2020/11/18 08:03 AM
                              Cinebench is NOT a representation of average workloadsDoug S2020/11/18 08:44 AM
                                Cinebench is NOT a representation of average workloadsDummond D. Slow2020/11/18 08:52 AM
                                  Cinebench is NOT a representation of average workloadsDoug S2020/11/18 03:59 PM
                                    Cinebench is NOT a representation of average workloadsDummond D. Slow2020/11/18 04:12 PM
                                      Cinebench is NOT a representation of average workloadsDoug S2020/11/19 10:19 AM
                                        Cinebench is NOT a representation of average workloadsDummond D. Slow2020/11/19 04:03 PM
                                          Cinebench is NOT a representation of average workloadsUngo2020/11/19 09:12 PM
                                            Cinebench is NOT a representation of average workloadsDummond D. Slow2020/11/20 09:45 AM
                                It's not really SMT or adding small coresDummond D. Slow2020/11/18 08:58 AM
                                  It's not really SMT or adding small coresDoug S2020/11/18 04:02 PM
                                    It's not really SMT or adding small coresDummond D. Slow2020/11/18 04:27 PM
                                Cinebench is NOT a representation of average workloadsxyz2020/11/18 01:14 PM
                                  Cinebench is NOT a representation of average workloadsMaynard Handley2020/11/18 01:54 PM
                                    Cinebench is NOT a representation of average workloadsGabriele Svelto2020/11/18 02:41 PM
                                      Cinebench is NOT a representation of average workloadsMaynard Handley2020/11/18 02:52 PM
                                        Cinebench is NOT a representation of average workloadsGabriele Svelto2020/11/18 03:05 PM
                            Cinebench is NOT a representation of average workloadsTJ2020/11/18 12:46 PM
                            SMT shines in IO heavy & commercial DB workloadsxyz2020/11/18 01:05 PM
                            "Average workloads" don't exist (NT)Foo_2020/11/19 03:55 AM
                          Apple loses a lot by not having turbo and SMTDummond D. Slow2020/11/18 08:02 AM
                            Apple loses a lot by not having turbo and SMTMaynard Handley2020/11/18 09:37 AM
                              Apple loses a lot by not having turbo and SMTDummond D. Slow2020/11/18 09:55 AM
                              Apple loses a lot by not having turbo and SMTDavid Hess2020/11/18 01:12 PM
                                Apple loses a lot by not having turbo and SMTMaynard Handley2020/11/18 02:12 PM
                                  Apple loses a lot by not having turbo and SMTJörn Engel2020/11/18 05:04 PM
                                    Apple loses a lot by not having turbo and SMTanonymou52020/11/18 05:37 PM
                                      Apple loses a lot by not having turbo and SMTJörn Engel2020/11/19 04:28 AM
                                  Apple loses a lot by not having turbo and SMTDavid Hess'2020/11/19 07:25 PM
                          Apple loses a lot by not having turbo and SMTAdrian2020/11/18 08:23 AM
                            Apple loses a lot by not having turbo and SMTgallier22020/11/19 12:21 AM
                              Apple loses a lot by not having turbo and SMTJames2020/11/19 02:22 AM
                                Apple loses a lot by not having turbo and SMTWilco2020/11/19 05:06 AM
                              Apple loses a lot by not having turbo and SMTanonymou52020/11/19 02:34 AM
                                Apple loses a lot by not having turbo and SMTgallier22020/11/19 09:04 AM
                                  big.LITTLE with different ISAsJames2020/11/19 09:41 AM
                                    big.LITTLE with different ISAsgallier22020/11/20 03:36 AM
                                    big.LITTLE with different ISAsanon2020/11/20 01:31 PM
                              Apple loses a lot by not having turbo and SMTAdrian2020/11/19 02:56 AM
                        Apple loses a lot by not having turbo and SMTJon Masters2020/11/18 12:46 PM
                          Apple loses a lot by not having turbo and SMTanonymou52020/11/18 03:41 PM
                          Apple loses a lot by not having turbo and SMTDummond D. Slow2020/11/18 04:17 PM
                            Apple loses a lot by not having turbo and SMTMaynard Handley2020/11/18 05:46 PM
                              Apple loses a lot by not having turbo and SMTJon Masters2020/11/19 12:31 AM
                                Apple loses a lot by not having turbo and SMTDummond D. Slow2020/11/19 07:01 AM
                              Apple loses a lot by not having turbo and SMTAdrian2020/11/19 02:50 AM
                                Apple loses a lot by not having turbo and SMTAdrian2020/11/19 03:10 AM
                                Apple loses a lot by not having turbo and SMTMaynard Handley2020/11/19 10:13 AM
                                  Apple loses a lot by not having turbo and SMTDummond D. Slow2020/11/19 04:10 PM
                        Apple loses a lot by not having turbo and SMTjuanrga2020/11/19 02:49 AM
                    re: "scaling"sr2020/11/17 12:39 PM
                      re: "scaling"Adrian2020/11/17 01:41 PM
                        re: "scaling"Adrian2020/11/17 01:52 PM
                          re: "scaling"Chester2020/11/17 06:29 PM
                  re: "scaling"anonymou52020/11/16 08:18 PM
                    re: "scaling"Maynard Handley2020/11/16 08:44 PM
        And the NZ'ers are first to deliver cinebench scoresDummond D. Slow2020/11/16 05:12 PM
          And the NZ'ers are first to deliver cinebench scoresMaynard Handley2020/11/16 05:31 PM
            And the NZ'ers are first to deliver cinebench scoresDummond D. Slow2020/11/16 05:46 PM
        And the NZ'ers are first to deliver cinebench scoresMaynard Handley2020/11/16 07:04 PM
          And the NZ'ers are first to deliver cinebench scoresDummond D. Slow2020/11/16 07:28 PM
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